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58,100 | Vehicle:
2005 Honda Accord LX 2.4L FI DOHC 4cyl Symptoms Car wouldn't start today. In the past had occasionally had it hiccup before starting but that was the only indicator of problems. No accidents or special maintenance done recently that seems to be linked to this issue. Did replace the starter twice (first one didn't last long), but that was about a year ago. Symptoms don't seem to be acting like it did with a bad starter. No Key Interior lights come on. Hitting brakes: Brake lights come on and interior lights dim. Turning headlights on: headlight indicator on dashboard blinks and interior light dims and blinks in sequence, can hear a clicking/grinding in sequence with the blinking. Under the hood can hear clicking/grinding more clearly and seems to be coming from near fuse box area. Honking horn causes symptoms of dimming lights, horn doesn't honk and grinding noise can be heard instead. Putting key in ignition Dashboard lights up like normal Previous symptoms plus dashboard blinks in sequence to headlight indicator and interior lights. Turning key to I position Radio can turn on (acts normal) Turning headlight on causes previous symptoms and radio goes off Trying to lower power window did not lower window (caused a grinding noise). Also stopped radio for a bit and caused lights to dim. Subsequent attempts to lower window did not cause radio to go off, did not cause lights to dim, and no grinding noise). Turning key to II position Lights dimmed, grinding noise (figured out this was the windshield wipers trying to move, as they moved slightly). Turning off windshield wipers removed grinding noise. Turning headlights on, windshield wipers on, or trying to use power windows caused lights to blink and interior lights as well as dashboard went dim. Radio turned off also. Gas gauge on dashboard jumped around and dropped to empty, other indicators on dashboard were blinking oddly and went dark after a few seconds. Was able to honk the horn a few times. After playing with the key a few other times (going back to off then position II again) wasn't able to get the horn to honk and instead got the grinding noise. When I was getting the grinding noise it cause the lights to dim, fuel gauge to go to empty, and radio to go off. Turn key to III position Everything dims or goes off (which seems normal to me) Starter doesn't seem to try to spin, though listening with the door open I do hear a single click noise so it sounds like it is trying to engage. Dashboard goes dim, ABS and Brake indicators on dashboard are faintly seen, go dark after a few seconds. Turn key back from III position to II position Fuel gauge jumps down, then jumps again to empty A bunch of the indicator lights on the dashboard turn on, the lights for the open doors blink rapidly 4 or 5 times and I hear a clicking noise for each of those blinks, then they all go dark. After a few seconds it returns to the state of "Turning key to II position" where the fuel gauge comes back up to current, radio comes back on, etc. Troubleshooting Removed the battery, brought it to AutoZone, they reported it tested GOOD. Bought a new multimeter (my previous one was broken) and tested the battery myself, was getting a reading of 12.78 VDC. Looked up online how to test relays, pulled quite a few fuses and relays from the hood fusebox, everything seemed to be indicating it was working ok (as far as fuses and relays themselves). Only thing that stood out was when I tried checking the voltage going to the headlight fuses, I was getting 0 VDC. Was able to get 12.78 VDC to some other fuse terminals (including the horn, which hasn't been working most of the time). I'm new when it comes to testing this electrical stuff, may have made a mistake, but I did hear clicking for each of the relays as I hooked them up to battery power and checked the resulting resistance of the other terminals on the relay. Checked the fuses to make sure resistance was near 0 (thought for some relays it seemed to jump around a lot, but some others went to 0 or close to it quickly). I didn't check every single fuse or every terminal. Not sure if I'm doing this completely correct and I've been at this for a few hours (and it is time to go to bed), so wanted some feedback to see if I'm doing this right or should focus on anything specific. Useful links Honda fuse box diagram What's next? Any idea to the nature of this issue? It seems pretty obviously to be electrical, but are we talking bad relay (all seemed good under the hood), bad fuse (all seemed good that I tested), or bad wire (I didn't seem to get a voltage reading to the headlight fuses, not the high or low beam for either left or right side headlights). Is this maybe a short? Do I need to trace the wiring from X to Y and check for any fraying, lose connections, etc.? Edit: Turned the headlights on and put the multimeter on the battery terminals. Voltage was jumping all around as I heard the same clicking noise before. Voltage was in the 9.XX range to 10.XX range. A few times it managed to jump up to a low 11.XX range. So it does seem like a battery issue. Will be swapping it out later when I get the chance and will confirm that this fixes my issue. Edit 2: Was able to jump start the car with another good vehicle. Wish I had tried that yesterday instead of the hours and hours of testing electrical connections. Thought I had been doing well by having the battery tested FIRST. Even tried with a multimeter to confirm, but should have tested it under load (forgot about that detail). Could have saved me quite a few hours and having to go into work late. Now I'm off to go buy a good battery and swap it out for this dead one. Thanks for the help everyone! | The symptoms all point to a faulty battery, and an incorrect test result for the Autozone battery test. Starting with this: Hitting brakes: Brake lights come on and interior lights dim: a good battery should have no problem driving both the brake lights and interior lights without dimming. The same goes for many of the other tests you've done. If switching on a component that draws 10 A causes dimming, your battery is never going to be able to supply several hundred A to the starter motor. Edit : Try testing the battery voltage under load. Switch on the headlights and measure the voltage. If it's still 12.7V on the battery terminals, one of the battery leads may be broken or corroded. If there's a big voltage drop, the battery is faulty. | {
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59,814 | A couple of weeks ago, the right headlight in my car burnt out, so I went to the garage and had it fixed. When I picked up my car, their salesnerd told me to watch my left headlight, for "once one headlight burns out, the other often follows in short order". At first, I found that statement a little odd. But indeed, last Friday (14 days since the previous blowout, 8 days since repair), my left headlight burned out. Was I just unlucky and the salesperson's tale is just superstition, or is this phenomenon an actual thing? If so, what causes it? Uneven load/voltage issues? For reference, my car is a 2013 Kia Rio UB. | No, the salesman was spot on. If you think about it, bulbs are designed to last about the same amount of time. If they are installed in pairs, then the secondary light which matches the first will most likely be on the road to death just as the first. This holds mostly true for higher output lights, like your headlights. Marker lights, being a much lower output, will not hold true to this. It is (IMHO) a good idea to replace headlights in pairs. Not only due to them lasting about the same amount of time, but also because as they get older, they start to dim. If you replace one headlight, there will be a distinct difference (in most cases) between the two. I guess that may not be an issue for everybody, but I'm just anal like that. I like the headlights to be even so as not to cause weird lighting effects across my field of vision at night. | {
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60,027 | I own a Ford Ecosport Diesel Turbo 1.5 TDCI. Every morning when I start the car, I put it on neutral and rev it up to 6K RPM for 3 seconds then bring it back to normal idling without revving and start my normal drive. The intention is to clear any carbon deposits inside the engine and exhaust. Is that a bad practice? My car is new and just reached 14000 KM.
When I started to do this, my car engine noise became less. | Yes, this may be bad. The oil is not yet at the operating temperature, and the same is true for engine parts as well. I wouldn't redline a cold engine with cold oil. Your intention to clear carbon deposits is justified. But why don't you do this during a drive? That way, the engine and oil have had a chance to heat up to operating temperature. By the way, are you sure the 6K RPM is the redline for your engine? Sounds a bit high for a diesel. | {
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60,595 | I have a Hyundai Excel 96 sedan, the AC is not working any more. I will eventually have a new AC system installed, but not now because it does cost some bucks. I'm planning to have it removed since it's just added weight, but I'm worried that if I have it removed now, afterwards when I would install the new AC system it will be harder since the old system was ripped out. So is it OK that I'll have it removed for now then install a new AC system probably next year? Or should I just let the AC system stay in the car until I have it replaced? | Keep the AC system in the car until you are ready to get it repaired. There's a load of parts to an AC system and some of them are hard to access, you are likely to spend much more in labor costs removing and then re-installing the system than any fuel savings from reduced weight. | {
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62,812 | This is something that I've always wondered. I'm no mechanic (web developer, actually) with very basic knowledge of vehicle mechanics so I can only guess at something like brake pipe pressure being involved, but that's about as far as I could guess. I can't find any article on the subject either, though I admit it's quite a niche question. Case in point; I'm leaving the motorway via a downhill off-ramp and come to a stop in the queue using the foot brake (still downhill) - I shift into neutral, apply the handbrake and release the foot brake. As I release the foot brake the rear of the car sinks, as though the suspension was being elevated by the foot brake, though I've no idea how this is possible. I apologise in advanced if this is rudimentary to those versed in vehicle mechanics and may be obvious. I've come to the assumption that it's normal behaviour and not an issue, but I can't remember whether or not this occurred with my previous two cars. If it's relevant, here's my vehicle information: Citroen Xsara Picasso Exclusive, 2006 (06),
1.6 HDI (Diesel) - 92HP,
Manual Transmission | With the handbrake on, the rear wheel is not able to rotate. When the foot brake is released the car will try to move forward. This will cause a rotational force on the rear tire. Since the rear tire cannot turn, the rotational force will be transferred to the axle mounting point 'A' which will cause the road spring to compress, hence lowering the car body. If you did the same thing going up hill, you will find that the body raises instead. | {
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63,699 | In a car with out four-wheel drive—if the car provides drive power on only two wheels—why put snow tires on all four wheels when the freeze sets in? Would it not be sufficient to change just the drive wheels? Is it just a question of use of the wheels and the extra use of two wheels for 12 months, while the other two pairs are being used nine months and three months would complicate things like wheel rotation? Related: need for matching tires on 4-wheel drive cars Edit : About braking : In this question we're more concerned about avoiding to get stuck. It's reasonably clear that having four winter tires offers better braking, but we are in this instant comparing four non-winter tires with two winter and two non-winter. Regardless, after you read Paulster's answer, it will be easy to extrapolate what would happen if your car was not oriented in the direction of motion and you attempted to brake, but someone who brakes during turns over snow or ice, with any kind of tires, is probably in a very bad position anyway. Context (edit #2, after Harper's answer) I am asking this question after giving up on moving from a parking lot, which required going up the mildest slope. After many, many, attempts I abandonned the car and used cabs for the day. Since I wasn't sure whether I could be towed from the rear of the car, I asked the question with the objective of buying two winter tires and installing them on the front wheels (on a FWD car). Curious phenomenon, by the way: if the wheels spin out (as they must if you're stuck), and if the temperature and snow underneath are in just the "right" conditions, the mere heat generated by a little bit of spinning (it's manual-drive and I was careful) will melt the snow and form a nice layer of pure, ultra-slick ice in very little time. But now we're way out of car mechanics and into the physics of water. In the evening the ice was less hard. Or maybe I managed to get out after pouring an obscene amount of salt, which may have acted as a gravel carpet more so than a melting point modifier. | What you are failing to realize is the non-drive axle provides stability. Yes, the two tires with power going to the ground needs traction to motivate the vehicle down the road, however, you still need to be able to control the vehicle. Regardless of whether your drive axle is up front or in the rear, the opposite axle provides the means to keep the vehicle on the road. Front Wheel Drive - Without traction on the rear end, it will tend to slip out from under the vehicle as you go around corners, causing you to spin out. Rear Wheel Drive - Without traction in the front end, you'll not have the same steering ability. Your car will tend to keep driving straight as you are trying to turn. In either case, if you need traction to go, you also need the traction to stop. Not having the traction on both axles severely limits your ability to get a moving vehicle slowed and stopped. If you need snow tires on one end of your vehicle, you need them on the other. EDIT: Special thanks to Kitsunemimi and Bob Cross for finding this video which directly talks to what I've said. | {
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64,583 | I have read that one should not leave greasy fingerprints on their spark plugs or on their light bulbs. Why is this a thing? On what else one should not leave fingerprints? How does one avoid leaving fingerprints (latex gloves or, say, cleaning the light bulb after putting it in)? How do you clean your fingerprints if you leave any? | Why is this a thing? For bulbs it is - spark plugs don't care. The problem with getting fingerprints on bulbs (specifically halogen-type bulbs) is actually the grease that gets left behind - the bulb will get quite hot when lit and grease on a portion of the bulb will cause differences in the rate of heating on the bulb surface and thanks to the way materials expand when heated this means you get different parts of the bulb expanding at different rates and... crack. Where the bulbs are made from quartz glass (such as in certain more powerful bulbs from some manufacturers) there is also the issue of devitrification - where the oils/salts left behind in the finger print can potentially cause the material to weaken although typically car bulbs aren't going to get hot enough for this to occur although some fogging of the glass may occur. On what else one should not leave finger prints? Probably a bit broad to answer here I'm afraid. How does one avoid leaving finger prints (latex gloves or cleaning say the light bulb after putting it in)? Yep clean latex gloves (cotton gloves are even better if you have them - but latex or nitrile works just fine) or a holding the bulb in a clean cloth works. How do you clean your finger prints if you leave any? You can clean them afterwards as well, a good wipe down with a clean microfibre cloth will do the job. | {
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66,857 | Earlier today, I stopped a little too far from an entrance I meant to use. I had to reverse to get back to it. I unconsciously pulled the handbrake up when I stopped (I think it is habit) so when I put the car in reverse, it refused to move. The road surface was very uneven so I thought the car just needed some coaxing to get moving. For this reason I depressed the accelerator quite far because the car was having an issue moving. I had not realised that the handbrake was up at this point. My friend in the passenger seat realised and alerted me before he put the handbrake down. I am very worried that I may have damaged the car in some way. Since this incident, it seems to be moving and stopping as normal. At first it made a bit of a weird rubbing sound when I stepped on the brake afterwards but I drove a further 20-25km since then and it has given me no indication of trouble. Is my concern and worry necessary? | You are not likely to have caused any damage in this situation. If you had driven 25 or 30 km with the handbrake on then yes there would be damage. | {
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66,863 | I have a C series 6000 CD in a 2006 Ford Fiesta originally sold in the Netherlands. None of the online radio code finder services have worked. Please provide the code so I can unlock my stereo. The numbers it displays is: C 040038 SA 811000. VIN is wfodxxgajd9k26934 Can you please give me the correct code? Thank you. | You are not likely to have caused any damage in this situation. If you had driven 25 or 30 km with the handbrake on then yes there would be damage. | {
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68,196 | I believe almost everyone working on a car in any capacity has heard this, many things should be tightened down in a criss-cross pattern. Why? What is the rationale behind it? I can imagine several plausible explanations myself, but I'd like to know what the actual reason behind it is. Why exactly is it that something will not seat correctly if it is tightened down in a clockwise pattern instead of criss-cross? | There is more to it than just a "criss-cross" pattern. You should also work your way out from the middle in stages of bolt torque. If you imagine tightening a cylinder head down starting at the two very ends. You have a gasket between the head and the block that doesn't really want to be crushed. When you tighten the ends down, the middle of the head will be being pushed up in an arch shape by the gasket, bending the head. With the ends of the head now locked in place by the end bolts, you now tighten the ones in the middle forcing the arch down. This will cause movement on the end bolts. There is a good chance now that the gasket will fail to do its job. If you work in stages from the middle out in a criss-cross pattern, the load is spread evenly without bending anything and gives the best chance of success. Additional by @Paulster2 - If you started torquing a head on one side and worked your way around, you are actually pushing the gasket ahead of your torque. As the gasket gets pushed around to where you started at, you now have a thicker portion which will cause a lump under the head, which would cause the head to warp. By criss-crossing your torque, you've eliminated this | {
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68,202 | How can I determine what type of clutch cylinder is on a Hyundai Santa Fe 2007? An auto mechanic who was giving me an estimate said if it was an "outer" type cylinder it would be very easy and cheap to repair, but if it was an "inner" cylinder it would be very expensive. In general how can I find out what type of part is in an old car... is there some online repository of repair manuals or something? The car is 4 wheel drive. I found some videos on YouTube about the clutch system but couldn't understand them. | There is more to it than just a "criss-cross" pattern. You should also work your way out from the middle in stages of bolt torque. If you imagine tightening a cylinder head down starting at the two very ends. You have a gasket between the head and the block that doesn't really want to be crushed. When you tighten the ends down, the middle of the head will be being pushed up in an arch shape by the gasket, bending the head. With the ends of the head now locked in place by the end bolts, you now tighten the ones in the middle forcing the arch down. This will cause movement on the end bolts. There is a good chance now that the gasket will fail to do its job. If you work in stages from the middle out in a criss-cross pattern, the load is spread evenly without bending anything and gives the best chance of success. Additional by @Paulster2 - If you started torquing a head on one side and worked your way around, you are actually pushing the gasket ahead of your torque. As the gasket gets pushed around to where you started at, you now have a thicker portion which will cause a lump under the head, which would cause the head to warp. By criss-crossing your torque, you've eliminated this | {
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68,217 | After driving for a few minutes above 60 mph when you apply the brakes the pedal goes to the floor. Pedal returns when pumped. All other times the brakes work fine. Took to Ford dealer they said it was the ABS system and made repairs. Drove truck again on the highway it happened again. Took back to Ford and they could not find anything wrong. Happened again. | There is more to it than just a "criss-cross" pattern. You should also work your way out from the middle in stages of bolt torque. If you imagine tightening a cylinder head down starting at the two very ends. You have a gasket between the head and the block that doesn't really want to be crushed. When you tighten the ends down, the middle of the head will be being pushed up in an arch shape by the gasket, bending the head. With the ends of the head now locked in place by the end bolts, you now tighten the ones in the middle forcing the arch down. This will cause movement on the end bolts. There is a good chance now that the gasket will fail to do its job. If you work in stages from the middle out in a criss-cross pattern, the load is spread evenly without bending anything and gives the best chance of success. Additional by @Paulster2 - If you started torquing a head on one side and worked your way around, you are actually pushing the gasket ahead of your torque. As the gasket gets pushed around to where you started at, you now have a thicker portion which will cause a lump under the head, which would cause the head to warp. By criss-crossing your torque, you've eliminated this | {
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69,288 | We have bought a used Toyota Yaris. Yesterday I allowed my kids to play in the car, and they discharged the battery... So I went to take it out to charge it up and I found pieces of a copper and copper coil in between the clamps and 'nips' of a battery. This is the first time I saw something like this. I am currently in the far North country (Lithuania) could this have anything to do with cold winters (-20 C). The battery is 44B20L (Wet 12V 35Ah) capacity. Why would one put copper in between battery contacts and clamps? P.S I might be overthinking this, could be they simply did this to tighter fit the clamps with the battery and used copper since it is a good conductor? Still, this is something I have never seen yet... | I think your guess will be correct. The clamp has probably been over-tightened in the past, has stretched and is no longer giving a good tight connection. The copper will have been added to act as a shim to make a tight connection. | {
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71,535 | When I change my oil I don't like going all the way back to the station to drop off the old oil and I don't want to pour it in the river, so I put 17 gals of premium in my 18 gal tank and then top off with my old oil. It's a regular gas car, not diesel. It runs a bit rough and I can barely see out the rear and it drives like it's underwater but a couple tanks later it runs like a champ. When I told my my friend who wrenches for a hobby he nearly blew a gasket, told me I'm lucky my car still runs and I can burn out my cat. I've been doing it for 7 years and haven't noticed problem. So, is this a bad idea or something? | It's a BAD idea! The oil is contaminated with impurities that will not do the fueling system on your car any favors. Further, it's bad for the environment because your car is NOT designed to burn oil even if it's mixed with gasoline. The best thing to do is to take the used oil to a place where it can be recycled into new oil and used again. Most oil change places accept it, many communities have recycling drop off locations, many auto parts stores take used motor oil. | {
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71,794 | Should I have the tire plugged, patched, or replaced? | That one looks too close to the sidewall. Bring $$ and replace. Reference Here Apparently that tire repair guidance originates from the guidelines set by the USTMA (U.S. Tire Manufacturer Assoc.) Now obviously that reference is designed to help sell tires, but its pretty safe, sound guidance. | {
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72,294 | I am considering getting a new engine for one of my cars and I was wondering if I'll have to change the odometer too. Since the car already has 220,000 miles on it, it would become a huge number if I used the same odometer on a new engine. | I wouldn't touch the odometer. The rule I always subscribe to is that the odometer measures how far the chassis has rolled. Otherwise a person could go mad trying to figure out which repairs/replacements should reset the clock. (Obviously not tires or wheels, but wheel bearings? Axles/driveshaft? Transmission/differential? etc...) It also makes sense when you think about the disconnect between the number of hours an engine has run vs. the distance it's traveled. Work trucks, limousines and police cars all can spend a significant amount of their life just idling, and that's not reflected in an odometer reading because the chassis never went anywhere in that time. | {
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72,662 | I was wondering why specific coolants or distilled water is used as a heat transfer liquid for engine cooling instead of just using a separate oil circuit with some type of oil as a heat transfer liquid. Cost issues aside I guess there is (could be created) an oil type available with similar properties (viscosity, heat transfer, heat capacity) to distilled water or coolant mixtures. Even if it would be necessary to re-design some engine elements (radiator tubes, coolant pumps etc) to cope for the differences in liquids properties wouldn't it be an advantage to have oils mixed in case of gasket failure and also if these two had the same properties (and since coolant liquid doesn't get extremely hot with use as to deteriorate) you could use the present "cooling" oil in engine oil changes. What might be some preventing issues with this idea? | There's a very straightforward answer to this question: Water has a much, much higher capability to transfer heat than oil. Even if you were able to overcome the safety and design issues brought up in other answers, you'd still have to overcome the fact that water has a huge performance advantage at transferring heat compared to other common fluids (including oil). Water is essentially the best possible fluid in terms of thermal conductivity; the only fluids that beat it are metals in liquid state (which isn't a practical choice for cooling a car engine made from metal itself). At 75 C, water's thermal conductivity is around .65 W/mK. Typical heat transfer oils are usually around .14 W/mK. Of course, coolant in a typical automobile isn't water, it's usually water mixed with alcohol. Typical mixes cause the conductivity to drop, because water also beats alcohol at heat transfer, but even pure ethylene glycol is .27 W/mK. A typical 50/50 mix puts you in the neighborhood of .45 W/mK, which means that typical water-based coolant has a thermal conductivity three times better than purpose-designed heat transfer oil. Let that sink in. If you wanted to cool your car's engine with heat transfer oil instead of typical water-based coolant, you're operating at a three to one disadvantage in terms of thermal conductivity. This basically means that your coolant system needs to be three times bigger in order to have the same capacity. Radiator size is already somewhat of a limiting factor in terms of how the front end of a vehicle is designed. I don't think anyone wants to drive a car where the radiator needs to be three times bigger than a typical car radiator is today. Oil is really only used for thermal transfer when water is impractical - due to corrosion, conductivity, evaporation, pressure or temperature requirements above what water can handle, or other limiting factors. As pointed out in other questions on mechanics.SE related to air vs water cooling, the transition to water cooled engines was basically because of this fact. An "air cooled" engine - which typically relies not only on air cooling, but also oil cooling - just can't compete. For a given application, if relying on oil or air cooling, you have to really limit your thermal load. In other words, for a given package size, it's easier to get more performance and efficiency with water cooling than with oil and/or air cooling. | {
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72,671 | I have a 2014 Kia Rio with a 6 speed auto. It asks for SP-IV specification transmission fluid. The transmission shop I am considering for a fluid change service, said that they use an all purpose Dexon6 fluid. They said they then add in a special friction modifier, which will then augment that fluid to meet different manufacturer specs. So they take the base fluid and add in the ford spec friction modifier for a for trans, and add in a kia spec friction modifier for a kia. Is this normal in the automotive service industry. Is this acceptable? Is this approved practice by OEMS? | There's a very straightforward answer to this question: Water has a much, much higher capability to transfer heat than oil. Even if you were able to overcome the safety and design issues brought up in other answers, you'd still have to overcome the fact that water has a huge performance advantage at transferring heat compared to other common fluids (including oil). Water is essentially the best possible fluid in terms of thermal conductivity; the only fluids that beat it are metals in liquid state (which isn't a practical choice for cooling a car engine made from metal itself). At 75 C, water's thermal conductivity is around .65 W/mK. Typical heat transfer oils are usually around .14 W/mK. Of course, coolant in a typical automobile isn't water, it's usually water mixed with alcohol. Typical mixes cause the conductivity to drop, because water also beats alcohol at heat transfer, but even pure ethylene glycol is .27 W/mK. A typical 50/50 mix puts you in the neighborhood of .45 W/mK, which means that typical water-based coolant has a thermal conductivity three times better than purpose-designed heat transfer oil. Let that sink in. If you wanted to cool your car's engine with heat transfer oil instead of typical water-based coolant, you're operating at a three to one disadvantage in terms of thermal conductivity. This basically means that your coolant system needs to be three times bigger in order to have the same capacity. Radiator size is already somewhat of a limiting factor in terms of how the front end of a vehicle is designed. I don't think anyone wants to drive a car where the radiator needs to be three times bigger than a typical car radiator is today. Oil is really only used for thermal transfer when water is impractical - due to corrosion, conductivity, evaporation, pressure or temperature requirements above what water can handle, or other limiting factors. As pointed out in other questions on mechanics.SE related to air vs water cooling, the transition to water cooled engines was basically because of this fact. An "air cooled" engine - which typically relies not only on air cooling, but also oil cooling - just can't compete. For a given application, if relying on oil or air cooling, you have to really limit your thermal load. In other words, for a given package size, it's easier to get more performance and efficiency with water cooling than with oil and/or air cooling. | {
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72,777 | For about the last year, a rat (or more) has been biting through the fuel line of my car and last month was the 4th time now. We have two cars in the garage at our place, but the rat is bothered about just this one car in particular. I have replaced the whole pipe 3 times now and after the 4th incident I did not bother replacing it. I have tried rat repellent sprays, rat cakes, rat repellent insulation tape, rat traps (cage with a bait) but this specific rat (or gang of rats) doesn't seem to care nor get caught in the trap. The surprising part is, it is biting off the fuel line at the very same spot every single time. I don't know what else to do now. What are my other options? | You could cover the pipe with some protective braiding like this - https://hoseflex.com/product/stainless-steel-braid/ | {
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72,785 | I have a problem with my Nissan Qashqai, its a late 2010 so its a facelift model. The lights flicker when I am driving, when im parked, basically all the time, my windows roll down slowly, some electronics have started dying, like my alarm system, and the latest is my rear & side mirror heaters. Any idea why is this happening ? its a 1.5 dci, original battery, and the voltage fluctuates, the flickering gets worse if ac is on, heated seats, or phone charger. I can turn everything off but it still continues to flicker. | You could cover the pipe with some protective braiding like this - https://hoseflex.com/product/stainless-steel-braid/ | {
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72,988 | I've read in various places that you should perform your first oil change on a new car at 1,000 miles or so. But the exact miles are available in the owner's manual. The owner's manual only states to change the oil every 5,000 miles. Should I go ahead and change it at 1,000 miles, then every 5,000 miles after that? Or should I wait until 5,000 miles for my first oil change? | The 1000 mile oil change is a holdover from days of yore. It falls into the "my grandfather /father (add appropriate generation) said you should always"... Add what ever urban myth was part of the lesson. Part of the reasoning was due to the Moly-Lube that was part of the engine assembly process. The theory was that the assembly lube was thick enough to clog the oil filter as the hot oil washed it off the bearing surfaces. So after 1000 miles the filter would cease to filter the oil. The improved assembly process and improved chemistry have made this no longer necessary. If it was a concern, the dealer would require it since they warranty the engine for 60,000 or up to 100,000 miles. | {
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72,995 | I live in a cold climate (northern Canada) where temperatures now are already -20C during the day. I have a 2007 Ford Fusion SEL 3L which doesn't get driven much and is parked outside, without a possibility to plug in. The battery keeps constantly freezing/breaking due to it not being charged enough so I wanted to replace it with an AGM battery to get some more life out of it. Trouble is that the battery is group size 96R, which is apparently a very odd size because there are no manufacturers that make AGM batteries in that size. 96R seems to be 9 9/16" x 6 13/16" x 6 7/8" What would be a good alternative size to look for? | The 1000 mile oil change is a holdover from days of yore. It falls into the "my grandfather /father (add appropriate generation) said you should always"... Add what ever urban myth was part of the lesson. Part of the reasoning was due to the Moly-Lube that was part of the engine assembly process. The theory was that the assembly lube was thick enough to clog the oil filter as the hot oil washed it off the bearing surfaces. So after 1000 miles the filter would cease to filter the oil. The improved assembly process and improved chemistry have made this no longer necessary. If it was a concern, the dealer would require it since they warranty the engine for 60,000 or up to 100,000 miles. | {
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73,163 | I need to park my car for about 5 years. I have a 2006 Civic with 244k miles.. I'm going to cover it and start it every 2 weeks.. someone told me that after that many years it's going to fall apart and is better to just sell it, not really sure what to do at this point. | Can you? Yes. Should you? Not in my opinion. 2006 Civics with 244k miles are a dime a dozen. Sell it and put the money in something like a savings or 5 year CD, then instead of losing money you will earn money. Cars sitting that long take a lot of care to prep properly and even then a lot of things that are usually lubed or turned tend to dry out and will need to be replaced. | {
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73,172 | I recently bought a 2019 Mitsubishi Xpander. This is my first time owning a car, and I'd like to know what are the basic periodic checks I should be doing. (the car manual is not in English, and I didn't manage to find an English one) | Can you? Yes. Should you? Not in my opinion. 2006 Civics with 244k miles are a dime a dozen. Sell it and put the money in something like a savings or 5 year CD, then instead of losing money you will earn money. Cars sitting that long take a lot of care to prep properly and even then a lot of things that are usually lubed or turned tend to dry out and will need to be replaced. | {
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73,561 | My parents have a 2001 Pontiac Aztek that's been sitting for two years. Apparently, before they stopped using it, there was an oil leak that caused starter problems (they couldn't find the leak), and they replaced it multiple times. And, the battery is as dead as dead gets...doesn't hold a charge to save its life. Based on the first part, I would assume it's a starter problem, but articles like this one: https://www.championautoparts.com/Parts-Matter/automotive-repair-and-maintenance/Car-Wont-Start.html , make me think the blame lies squarely with the battery, because it does turn over without any clicking or weird noises. However, it only turns over when hooked up to another car, but even after leaving it jumped for 30 minutes, it was still barely (slowly) turning over. The headlights are bright when I turn them on, while being jumped, but dim significantly when trying to start the car. Electronics seem to work, and the only warning light I get is for the battery. First question: should a car with a completely dead battery always start while being jumped if there are no other problems? Second: can a starter or alternator go bad without any weird noises? Update : I got it started, woohoo! I replaced the battery (which was way more difficult than it should have been), and got the car started. However, the following things happened: my first time turning the key, the car turned over and then stopped. I thought maybe the battery was low quality, so I jumped it. Car clicked over and over without turning over. Tried again, click, click, click, then nothing. Fiddled with the jumper cables, tried again. The car started turning, then grinding, then smoke. Based on a quick search, it seemed the starter was gone. Tried again, and after a few turns, it started! I was really excited, and thought it would start again, so I shut it off. It didn't. I tried a few more times..more clicking, more turning off. After maybe thre more tries, it started again. I reved the engine to hopefully clear air or old fuel from the lines. I took it out for a quick drive and gassed up a bit. When I first started the car, a lot of really thick exhaust came out, but it seemed to clear up when I put more gas in it. So, is this definitely a starter problem? Also, the starter was replaced recently before the car was parked. My sister told me the starter went out twice because of an oil leak that can't be pinpointed. Does this sound plausible? | If the battery is completely dead, especially after sitting for two years, it most likely won't take a charge. Without the battery getting charged, you most likely don't have enough juice coming through the jumper cables to give it the power it needs to turn the Aztec over. Double check the voltage at the battery without the jumper cables on it. If it is still low (or non-existent), replace the battery. I would bet this will solve your issue. You'd have to be using some heavy duty jumper cables (I'm thinking 2-gauge or larger) to pass enough current through them to get an engine to start with a completely dead battery. Most regular jumper cables aren't anywhere close to this. As far as your second question about the starter/alternator going bad without any weird noises ... sure, but first things first. Change out the battery or get it fully charged, then work on separate issues. Usually, a starter and/or alternator will not go bad just sitting for long periods of time. Also, don't pay any attention to the battery light until after you get it started ... it isn't really stating the battery is bad ... it's there to tell you there's an issue with the charging system in general. If the engine isn't running, you won't be charging anything ;-) | {
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73,569 | I know what causes battery terminal corrosion but I've sort of got a dilemma. The long screw that holds the battery in place corroded to a concerning degree. It looked just like the positive terminal on a battery that's corroded. I took it off, cleaned it up and found that it's almost been corroded away. It sort of looks like someone just dropped battery acid on it for the heck of it. Anyway I'll attach a picture of the screw after cleaning, it's just strange. Anyone have any ideas? | If the battery is completely dead, especially after sitting for two years, it most likely won't take a charge. Without the battery getting charged, you most likely don't have enough juice coming through the jumper cables to give it the power it needs to turn the Aztec over. Double check the voltage at the battery without the jumper cables on it. If it is still low (or non-existent), replace the battery. I would bet this will solve your issue. You'd have to be using some heavy duty jumper cables (I'm thinking 2-gauge or larger) to pass enough current through them to get an engine to start with a completely dead battery. Most regular jumper cables aren't anywhere close to this. As far as your second question about the starter/alternator going bad without any weird noises ... sure, but first things first. Change out the battery or get it fully charged, then work on separate issues. Usually, a starter and/or alternator will not go bad just sitting for long periods of time. Also, don't pay any attention to the battery light until after you get it started ... it isn't really stating the battery is bad ... it's there to tell you there's an issue with the charging system in general. If the engine isn't running, you won't be charging anything ;-) | {
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74,046 | In the morning, my Honda Aviator scooter takes too much time to kick start and once started then it will start easily the next time in two to three kicks. The electric starter is not working due to a dead battery. I consulted with a mechanic and he said that it could be because of the battery problem but I am not convinced that this is the reason. A second possible reason could be an issue with the valves. So can anybody tell me what the probable reason may be? | Your Aviator has an ignition coil, rather than a magneto, to generate the spark. That means that it relies on the battery to have enough charge to generate the spark, so likely the ignition is only producing sparks once you've cranked the engine over enough to put a little charge into the battery. Engines with magnetos that generate the spark directly from the rotation of the crank - there's a magnet in the magneto rotor that excites the ignition coil separately from the generator coils that power the charging and lights - can start even if the battery is completely flat, but yours will not. Conclusion - it's likely that you battery is not holding any charge after running, so you will need to replace it. | {
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74,496 | I have read many warnings about driving a car through deep water. Some problems that this can cause is destroy the catalytic converter and in petrol engines water can cause damage to spark plugs. And in diesel cars I thought you needed a special exhaust if you want to drive with the engine underwater. And I also saw a video about a car that had its engine destroyed. How much of this is true? And how do those 4 wheel drive cars drive with their engines submerged in muddy water ? I have myself driven a Toyota yaris through water as high as the top of its wheels and nothing happened although I did keep the engine on high revolutions. What is the recommended thing to do if you need to pass through an area that's been flooded? (Ofcourse the answer will depend on the car) I have seen many videos and pictures of cars driving through deep water and here are two examples:
1. https://m.youtube.com/watch?v=ednZi2T-TsA&t=58s 2. https://m.youtube.com/watch?v=LC5ld79joIA | One of your questions as stated and not answered is: What is the recommended thing to do if you need to pass through an area that's been flooded? The answer to this has nothing to do with Mechanics.SE, but I'll answer it anyway ... Bottom line: DON'T DO IT. It has nothing to do with whether your car can run through the water and survive. It has EVERYTHING to do with if you can survive. The big problem here is, you cannot see what is under the water. You cannot see if the road has been washed out. You cannot tell if it is safe to drive through, regardless of whether or not your car can even make it through it. In some areas when the area is flooded, the water may look calm, however there may be currents which can sweep your vehicle off of the roadway. When this happens, you have absolutely no control. You run the SEVERE risk of drowning in a situation such as this. This is the MAIN reason you should not drive your vehicle in a flooded area. | {
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76,558 | I recently purchased a CRF50 dirt bike and was going to do an oil change on it. I was talking with a friend and they recommended I take the following steps when I do my first oil change to help "clear things out": Drain oil Remove spark plug Fill Crank case with gasoline through oil filler opening Cycle the kickstarter several times Drain the gasoline Fill with oil I don't know a lot about cars/motorcycles but I've never heard of anyone doing this and it sounds a little sketchy to me. Would doing this potentially damage the engine? Does doing this actually help clean the engine? | Gasoline flushes the oil out of the very spots where you need lubrication, so the next time you start it, the bearing surfaces are "dry" until the oil pressure builds up enough to relubricate them. This technique is mechanic folklore and should not ever have been done. If you think the current oil is excessively dirty, there are engine "detergent" products that you can add to the old oil and run for a while to help free up sludge and dirt and get it down into the oil sump. Not only is it a fire hazard (as noted above in one of the comments) it's extremely hard on your engine. Don't do it!! | {
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77,846 | The other week, my friend was trying to jump start a friend's very dead car battery with one of the portable power bank car jump starter kits. It looked something like the below: Image source If I were to have been jumping the dead car with another car, I would have given the dead car's battery a good long charge from the donor car before trying to start it. I am wondering, can one "charge" a dead battery by leaving one of these portable jump kits connected for like 10 minutes? Or are these jump kits meant solely to provide a enough juice just for a jump. | As Miracle Max would say , there's two kinds of dead batteries, and there's a big difference between them. Mostly Dead This is the most common kind of dead battery. Let's say your battery is rated for 300 cold cranking amps. After several years of use, it degrades until it reaches, say, 250 amps. Your battery isn't out of power, it just can't get your engine over the hump of cranking amps. Incidentally, in this scenario, "letting the battery charge" won't help because the battery is no longer capable of holding sufficient charge. Jumping in this scenario works by borrowing the remaining amps from an external source. This is why even a small car can often jump a large pickup. You can even buy battery chargers that can plug into a wall and will give you that boost as well (both batteries and wall chargers do this via a capacitor). These smaller jumping batteries are designed to give you surge in cranking amps for a single moment to give you that extra push. Depending on the device, that could be as little as 100 amps or as many as 2000. All Dead After you've gone through the battery's pockets for loose change... wait, we're talking batteries. Sorry, Max. An "all dead" battery is really a good battery that is mostly or fully depleted (i.e. you ran your car radio with the engine off for a long time or your alternator died). This is a less common problem, but it still happens. A pure surge battery isn't designed help you directly with this problem because it's generally designed to offer a one-time boost. Your lead-acid car battery really wouldn't like getting 500 amps all at once. Lead acid batteries like a slow, steady charge. Most wall-powered chargers run 15-30A in charging mode and you'll need to charge it for some time (meaning several hours) to get it back up to full. If I were to have been jumping the dead car with another car, I would have given the dead car's battery a good long charge from the donor car before trying to start it. The reason people are taught to "let the car charge a bit" first in jumping is that you need the dead battery to provide some power in the attempt to crank. Since you're probably not carrying a battery tester with you, there's no way to know why the battery is bad, and there's no harm in letting a "mostly dead" battery charge for a minute. If you're using a battery pack, just hook and crank. If the battery is all dead, the alternator will recharge it naturally. If the battery is mostly dead, it will provide the missing amps. Go take it to a car parts place and they can test it for free and tell you if you need a new battery. | {
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77,860 | I own a Ford Fiesta 2006 when my car is turned off my cigarette lighter stays on as I only have one I use a 3 way cigarette lighter plug splitter adapter I use one port for the dash cam and one for an fm transmitter. The other one is turned off so no power is going there. The device it self has an on/off button at the bottom so I’m wondering if I can keep it plugged in to the cigarette light and when not in use I can use the on/off button to turn the whole thing completely off, will doing this still use my car battery? Thanks for your help in advance | As Miracle Max would say , there's two kinds of dead batteries, and there's a big difference between them. Mostly Dead This is the most common kind of dead battery. Let's say your battery is rated for 300 cold cranking amps. After several years of use, it degrades until it reaches, say, 250 amps. Your battery isn't out of power, it just can't get your engine over the hump of cranking amps. Incidentally, in this scenario, "letting the battery charge" won't help because the battery is no longer capable of holding sufficient charge. Jumping in this scenario works by borrowing the remaining amps from an external source. This is why even a small car can often jump a large pickup. You can even buy battery chargers that can plug into a wall and will give you that boost as well (both batteries and wall chargers do this via a capacitor). These smaller jumping batteries are designed to give you surge in cranking amps for a single moment to give you that extra push. Depending on the device, that could be as little as 100 amps or as many as 2000. All Dead After you've gone through the battery's pockets for loose change... wait, we're talking batteries. Sorry, Max. An "all dead" battery is really a good battery that is mostly or fully depleted (i.e. you ran your car radio with the engine off for a long time or your alternator died). This is a less common problem, but it still happens. A pure surge battery isn't designed help you directly with this problem because it's generally designed to offer a one-time boost. Your lead-acid car battery really wouldn't like getting 500 amps all at once. Lead acid batteries like a slow, steady charge. Most wall-powered chargers run 15-30A in charging mode and you'll need to charge it for some time (meaning several hours) to get it back up to full. If I were to have been jumping the dead car with another car, I would have given the dead car's battery a good long charge from the donor car before trying to start it. The reason people are taught to "let the car charge a bit" first in jumping is that you need the dead battery to provide some power in the attempt to crank. Since you're probably not carrying a battery tester with you, there's no way to know why the battery is bad, and there's no harm in letting a "mostly dead" battery charge for a minute. If you're using a battery pack, just hook and crank. If the battery is all dead, the alternator will recharge it naturally. If the battery is mostly dead, it will provide the missing amps. Go take it to a car parts place and they can test it for free and tell you if you need a new battery. | {
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77,864 | So I got some steering issues with my E150 Ford van from 1998 with a 5.4 v8 in it. It kinda groans and creaks like a giant wooden ship from the 1600s when ya turn it. Somebody on here was tellin me I outta get it checked out asap on account of it bein dangerous. But I was just wondering: if yer ball joints were to snap off or whatever... if that would really be all that dangerous... cuz I figure... the wheel would just kinda dangle like a shopping cart cuz it's still attached by a million arms and struts and whatever... but as long as at least one of the front wheels is still attached to the ball joint, then you should still be able to steer the vehicle to safety in such an emergency situation... am I wrong? What I'm really scared of is if I'm drivin and I see one of the front wheels just rollin on into the horizon! Then you gotta think about which way you turn the vehicle for sure. | As Miracle Max would say , there's two kinds of dead batteries, and there's a big difference between them. Mostly Dead This is the most common kind of dead battery. Let's say your battery is rated for 300 cold cranking amps. After several years of use, it degrades until it reaches, say, 250 amps. Your battery isn't out of power, it just can't get your engine over the hump of cranking amps. Incidentally, in this scenario, "letting the battery charge" won't help because the battery is no longer capable of holding sufficient charge. Jumping in this scenario works by borrowing the remaining amps from an external source. This is why even a small car can often jump a large pickup. You can even buy battery chargers that can plug into a wall and will give you that boost as well (both batteries and wall chargers do this via a capacitor). These smaller jumping batteries are designed to give you surge in cranking amps for a single moment to give you that extra push. Depending on the device, that could be as little as 100 amps or as many as 2000. All Dead After you've gone through the battery's pockets for loose change... wait, we're talking batteries. Sorry, Max. An "all dead" battery is really a good battery that is mostly or fully depleted (i.e. you ran your car radio with the engine off for a long time or your alternator died). This is a less common problem, but it still happens. A pure surge battery isn't designed help you directly with this problem because it's generally designed to offer a one-time boost. Your lead-acid car battery really wouldn't like getting 500 amps all at once. Lead acid batteries like a slow, steady charge. Most wall-powered chargers run 15-30A in charging mode and you'll need to charge it for some time (meaning several hours) to get it back up to full. If I were to have been jumping the dead car with another car, I would have given the dead car's battery a good long charge from the donor car before trying to start it. The reason people are taught to "let the car charge a bit" first in jumping is that you need the dead battery to provide some power in the attempt to crank. Since you're probably not carrying a battery tester with you, there's no way to know why the battery is bad, and there's no harm in letting a "mostly dead" battery charge for a minute. If you're using a battery pack, just hook and crank. If the battery is all dead, the alternator will recharge it naturally. If the battery is mostly dead, it will provide the missing amps. Go take it to a car parts place and they can test it for free and tell you if you need a new battery. | {
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79,426 | I know similar questions have been asked but I'm specifically looking for the most cost efficient way to solve the following problem. I have a 2006 Lexus RX400h for which the physical door key does not fit the lock cylinder of the door (but it does start the car). I open the car door with the key fob. I bought the car this way so I don't know the exact backstory. The fact that my physical car key does not open the door lock cylinder does not usually bother me. But when the battery dies, I am unable to get into my own car. So I'd like to resolve this situation. After speaking with some folks, I believe the previous owners probably changed the ignition cylinder without changing the door locks. Then they just reprogrammed the key fob to open the door and to start the car. My current thinking is the following: It seems like changing the door lock cylinder is probably more expensive than changing the ignition cylinder back to factory specs and then getting a factory key and program that key to open and start the car. I could get all of this done with my local Lexus dealership. But knowing dealerships, I am certain that this will be expensive. I also feel like I cannot get reliable information from the dealership, a mechanic, or a locksmith because all of them have an interest in selling me their services. So now my question is what would be the least expensive way to deal with this? | Being a auto locksmith, I can 100% recommend that you have your door lock rekeyed to match your current ignition key. Cost will depend on location and if you remove the the lock yourself and take it to a shop or if you call a reputable mobile smith to come out. I charge about $90 for mobile service and a simple rekey like this. The lock is simple to remove, there is a set screw on the side of door frame you undo and the lock pulls out to remove. I guess a shop would charge about $50. Rekeying ignition is not as easy because these are somewhat sealed units and need a little drilling to open up so it will cost more. I'd say more along the lines of $100 shop/ $200 mobile. PLUS you will need to have a new case cut to move transponder in or new key programmed all together to match back to the ignition which will be in addition to the ignition rekey cost. Dealer has no idea how to rekey anything. They will just replace stuff. I wouldn't bother with them in this case. Its also possible your door lock is just seized up. It is very common on lexus locks around those years. Bad grease that dries up. Spray a healthy bit of wd40 in there and work your key in and out some. If still does not work take the lock out and spray MORE wd40 in the big drain hole underneath the lock while putting your key in and out. | {
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79,516 | I have an 08 ford focus that I haven't been driving. I just turn it on and let it run for about 30 minutes every few weeks so that it's not just sitting. One time I left it running in the parking lot and forgot about it until 14 hours later. How bad is this? What kind of damage could I expect from this? | There's probably no damage at all, the engine just ran at low revs for a long time. One issue you may have is if it ran out of fuel the line may have sucked sediment from the bottom of the fuel tank and drawn it into the fuel filter, which can clog the filter up. If you notice it's lagging a bit in the future what's what I'd look at. Fortunately fuel filter replacements are cheap. Also, some fuel pumps are designed to sit in the fuel tank and be cooled by the fuel, running very low on fuel could overheat the fuel pump, this could also lead to insufficient fuel pressure, especially at higher revs, however it's unlikely a single instance would cause that much damage. Incidentally, just letting your car idle isn't good enough, you need to actually drive the car around to keep everything working and the tires circular. A 20 minute drive once per week will keep the battery charged and everything working. | {
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80,359 | Last week I was driving a motorcycle. When I stopped at a traffic light I noticed the rear suspension dropped a little when I released the rear brake. Later I noticed my car did the same thing. When you suddenly stop, but not release the brake the suspension appears to be locked ("frozen") (See below image). When you do release the brake, the cars suspension appears to drop down to its resting position. But why is this? As far as I know parts of the brakes (brake rotors, calipers, drums and shoes) are not connected to the moving suspension parts such as the damper spring, damper and stabilizer. Also the suspension does not require the wheels to move in order to move. You can just as easily bounce the suspension while the car is parked. Can someone explain to me how this works? | I made a crude sketch illustrating the relevant points of the shown image. Brakes engaged: The center of gravity is above ground, the brakes "try" to slow down the car, the car itself "wants" to move further forward. The front "sinks", compressing the front struts (orange). The rear "raises", thereby allowing the rear suspension (blue) to "open". As a consequence the distance between front and rear wheels (red) gets smaller (teal line). When the car is now at a complete stop: The applied brakes keep the wheels from turning, thereby the distance between the wheels remains the same. This is now important: The contact points of the wheels, combined with the pivot (purple circle) of the rear suspension form a triangle (purple lines). A triangle with fixed lengths allows no movement. Thereby the rear stays raised. The front wheels have only a small effect as they have a pure vertical freedom, excluding every horizontal movement. Brakes released The relaxed brakes allow the wheels to roll freely. The "blocking" triangle now gets "deactivated" as the distance between the wheels is now variable. The now opened wheels allow the rear suspension (blue lever) to "close" as the rear of car still weights down on the rear wheels through the springs. | {
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80,388 | When shifting from any gear other than 1st (while standing still, obviously), sometimes the reverse gear doesn't fully engage and the shifter will pop back to neutral. So I have to shift to 1st gear first and then to reverse for it to fully engage. When shifting from 1st gear to reverse, sometimes the reverse gear doesn't fully engage and I have to shift to 2nd first before shifting to reverse. I have observed this behaviour in multiple manual transmission cars, but it's most notable in my work's Peugeot 207. I understand the basic workings of a manual transmission, how gears are selected by attaching the gear to the output shaft using a sleeve and how each gear (except reverse) uses a synchronizer ring to synchronize the gear speed with the speed of the output shaft, but I don't understand how the general design of a manual gearbox leads to this behavior. Can someone explain this to me? | It's common for manual transmissions to not have the same gear syncronizing mechanism on reverse gear as it does on forward gears. The job of the synchronizer is not just to match the speeds of cogs that are about to mate, but to align the teeth so that they slide and interleave with each other. While reverse gears would ideally have the same alignment sync property they don't typically need the rotational speed sync mechanism because we (should/could) only shift into reverse when the vehicle is stationary I suspect that you frequently manage to engage your reverse gears in such a way that the teeth bang into each other rather than interleaving as they should; perhaps you notice that when you "miss" reverse even though the stick looks like it's in the right "slot", it's not "fully back/forwards" compared to where it normally is. Moving to another gear causes a shift in the gear positions in the box and after this reverse is able to engage. Other actions, such as briefly raising the clutch or letting the car roll would also shift the cog positions, allowing the teeth to mate, though arguably the safest route is the one you currently take. In terms of what's wrong, perhaps the previous owner played "if you can't find it, grind it" often with the reverse gear and has worn the teeth, that used to have meeting angled faces that assisted alignment, so that one or both now have flat spots; occasionally these flat spots collide directly, and cannot perform their function of causing cog rotation/alignment as they slide past each other: Image credit: Note that this image above makes most sense in combination with the following image: The conical shape of the pink cog synchronizes the speeds, then it is the job of the angled faces on the two mating cogs to align the teeth. A reverse gear doesn't need the conical portion but it still needs angled teeth. Imagine what could happen some percentage of the time if the points of the angled teeth were worn flat so they engaged flat-to-flat rather than slope-to-slope: It's an exaggerated image to make the point; teeth shaped with a flat will not engage if the flats meet (left diagram) but will if the slopes meet (right diagam), giving rise to a percentage risk of collide rather than slide. If your gear teeth happen to randomly be in the right place, reverse will engage. If in the wrong place, you have to do something to jiggle the gear positions | {
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81,833 | Got a 1998 Toyota Camry that has an empty battery and am wondering what the best course of action is. I have a battery charger that I am thinking of using but it's currently inconvenient to do. My question is: If I just jump start the car and run it for long enough to charge the battery, is this the same as charging the battery with a battery charger? Or would there be benefit to using the battery charger? I plan on running everyday to keep the battery charged. ________________________________ Added: The car had been unregistered for a while and wasn't driven for an extended period (~3 months) which has lead to the battery running flat. I am not 100% on the age of the battery but it doesn't "look" that old but I know that may not matter. At this point I know the car needs a new battery eventually, but to get it registered it needs to be seen by a mechanic and have a few things done and checked. Until then just want to get the car running again to keep it in good condition. | Got a 1998 Toyota Camry that has an empty battery and am wondering what the best course of action is. Why is it empty? Is it empty because the battery is old and dying and won't hold capacity? Or is it empty because you yesterday forgot the lights on? The correct course of action depends on the reason for it being empty. If the battery is good but you just forgot the lights on, and it has been empty only for a short duration of time (lead-acid batteries don't like extended deep discharge), then go ahead and jump start the car. That's the fastest way. You have to be careful when driving the car afterwards because if you accidentally misuse the clutch and cause the engine to stall, there's a risk you can't start it again. But with a little bit of care, you can drive it. If the battery is empty because it is old and dying, do not jump start it ! The problem is that when jump starting, it is actually the donor battery providing charge. When you disconnect the donor vehicle, the only good battery in the electrical system goes away. The dying old battery in the recipient car can't act as a buffer for the electrical system. The alternator can then produce voltage spikes, destroying expensive electronic equipment all around the car. The newer the recipient car is, the more damage you will see. I would say 1998 car has enough electronics that you don't want to destroy all of them. So with an old and dying battery, you can try to see whether charging will remedy the situation. You can charge it slowly with a battery charger or rapidly from a donor car with jump start leads, but in that case don't turn the recipient car engine on. Then check to see whether the old battery is able to start the engine (with charger / jump start leads disconnected). If not, it's time to purchase a new battery. If it can start the engine, keep an eye of the situation and estimate when you need the new battery, if you need it at all. If you forgot the lights on, and then left the battery sit for a week or two not bothering to fix the situation, then the health of the battery is unknown -- on one hand, the battery was good before the event, but on the other hand, lead acid batteries don't like extended deep discharge. So it is possible the deep discharge has damaged the battery. It's always safer to charge and then try starting than to jump start. | {
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81,847 | I recently got a cap for my 2012 Toyota Tundra and am wiring in the brake lights on it. I was planning on pulling off of the existing brake light but there are 3 wires going into it and only 2 going into my truck cap brake light. There is a black, solid green, and green + red stripe wire and I am not sure which is which. What are each of these wires and what do I need to hookup to get the brake light working? | Got a 1998 Toyota Camry that has an empty battery and am wondering what the best course of action is. Why is it empty? Is it empty because the battery is old and dying and won't hold capacity? Or is it empty because you yesterday forgot the lights on? The correct course of action depends on the reason for it being empty. If the battery is good but you just forgot the lights on, and it has been empty only for a short duration of time (lead-acid batteries don't like extended deep discharge), then go ahead and jump start the car. That's the fastest way. You have to be careful when driving the car afterwards because if you accidentally misuse the clutch and cause the engine to stall, there's a risk you can't start it again. But with a little bit of care, you can drive it. If the battery is empty because it is old and dying, do not jump start it ! The problem is that when jump starting, it is actually the donor battery providing charge. When you disconnect the donor vehicle, the only good battery in the electrical system goes away. The dying old battery in the recipient car can't act as a buffer for the electrical system. The alternator can then produce voltage spikes, destroying expensive electronic equipment all around the car. The newer the recipient car is, the more damage you will see. I would say 1998 car has enough electronics that you don't want to destroy all of them. So with an old and dying battery, you can try to see whether charging will remedy the situation. You can charge it slowly with a battery charger or rapidly from a donor car with jump start leads, but in that case don't turn the recipient car engine on. Then check to see whether the old battery is able to start the engine (with charger / jump start leads disconnected). If not, it's time to purchase a new battery. If it can start the engine, keep an eye of the situation and estimate when you need the new battery, if you need it at all. If you forgot the lights on, and then left the battery sit for a week or two not bothering to fix the situation, then the health of the battery is unknown -- on one hand, the battery was good before the event, but on the other hand, lead acid batteries don't like extended deep discharge. So it is possible the deep discharge has damaged the battery. It's always safer to charge and then try starting than to jump start. | {
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81,856 | I drive a 2015 Mercedes S63 AMG 4matic. The rear wheels are staggered with 285-35-20 tires on 20/9.5 wheels, while the front tires are 255-40-20 on 20/8.5 wheel. The current rear tire size only comes in a summer tire and I need all season tires on the car. Therefore, I want to buy 4 all season tires sized like the front wheels. | Got a 1998 Toyota Camry that has an empty battery and am wondering what the best course of action is. Why is it empty? Is it empty because the battery is old and dying and won't hold capacity? Or is it empty because you yesterday forgot the lights on? The correct course of action depends on the reason for it being empty. If the battery is good but you just forgot the lights on, and it has been empty only for a short duration of time (lead-acid batteries don't like extended deep discharge), then go ahead and jump start the car. That's the fastest way. You have to be careful when driving the car afterwards because if you accidentally misuse the clutch and cause the engine to stall, there's a risk you can't start it again. But with a little bit of care, you can drive it. If the battery is empty because it is old and dying, do not jump start it ! The problem is that when jump starting, it is actually the donor battery providing charge. When you disconnect the donor vehicle, the only good battery in the electrical system goes away. The dying old battery in the recipient car can't act as a buffer for the electrical system. The alternator can then produce voltage spikes, destroying expensive electronic equipment all around the car. The newer the recipient car is, the more damage you will see. I would say 1998 car has enough electronics that you don't want to destroy all of them. So with an old and dying battery, you can try to see whether charging will remedy the situation. You can charge it slowly with a battery charger or rapidly from a donor car with jump start leads, but in that case don't turn the recipient car engine on. Then check to see whether the old battery is able to start the engine (with charger / jump start leads disconnected). If not, it's time to purchase a new battery. If it can start the engine, keep an eye of the situation and estimate when you need the new battery, if you need it at all. If you forgot the lights on, and then left the battery sit for a week or two not bothering to fix the situation, then the health of the battery is unknown -- on one hand, the battery was good before the event, but on the other hand, lead acid batteries don't like extended deep discharge. So it is possible the deep discharge has damaged the battery. It's always safer to charge and then try starting than to jump start. | {
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81,913 | The key feature of antifreeze--as the name implies--is that it doesn't freeze. When I was a kid, my Dad used to use just plain water in the radiator of his 1967 Oldsmobile Cutlass during the summer. It worked ok. He'd only use antifreeze in winter. Since salt significantly lowers the freezing temperature of water from 32 to -6F (0 to -21C) [1], can salt water be used as a cheap alternative to antifreeze in winter and below-freezing temperatures? https://van.physics.illinois.edu/qa/listing.php?id=18774&t=lower-freezing-point-to--10%B0f#:~:text=There's%20only%20a%20certain%20amount,%2C%20or%20%2D6%C2%B0F . | Uh ... absolutely not . Salt water will cause corrosion with in the engine block. Salt water is an electrolyte, so will pass electricity which will cause electrolysis . Also, it might be able to handle a bit lower/higher temps than straight water, it doesn't work as well as antifreeze. Antifreeze is usually good to -40°F/-40°C, plus it protects your engine from electrolysis and corrosion. I'd use straight water before I'd use saltwater ... not something which is good for your engine. | {
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81,914 | I drove my car (Fiat Panda Active) through a flood that was deeper than I expected, it stalled, I restarted it again, it struggled once more when I got out of the flood but kept going. I then had the engine off for about 10 minutes to run an errand then drove for about 150 miles to reach my final destination, and my car drove fine all the way there. I realise now that I shouldn’t have started the car in the flood (or attempted to drive through the flood in the first place without being absolutely sure of the depth!), and that I will need to check the oil for water contamination, but if my car started and drove okay does that mean I managed to escape ruining the engine? | Uh ... absolutely not . Salt water will cause corrosion with in the engine block. Salt water is an electrolyte, so will pass electricity which will cause electrolysis . Also, it might be able to handle a bit lower/higher temps than straight water, it doesn't work as well as antifreeze. Antifreeze is usually good to -40°F/-40°C, plus it protects your engine from electrolysis and corrosion. I'd use straight water before I'd use saltwater ... not something which is good for your engine. | {
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83,129 | How can I start my Corvette without having to go to the dealership to get a new key? My money situation is tight, so I'm trying to find a way to start my car, without having to pop the clutch or order a new key. | Short answer, you can not. Your car is equipped with an immobilizer. With out a properly coded key/transponder chip you will not be able to start your car. It disables fuel and spark. Its possible you could get the immobilizer tuned out of your ecu but this is much more complicated and expensive so not worth mentioning plus you would still need a key to unlock the steering. Your cheapest method will be to get a key from dealer with your registration and photo ID, then program the transponder yourself. Your easiest option is to call a mobile reputable locksmith to come out and generate a new key and program it for you. | {
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83,133 | I have a 2015 Honda CRV. I just got my tires replaced. After driving a few miles, the TPMS alert goes off and keeps going off even after I've reset the alert. I've checked my tires several times along my trip home and also after I let the tires cool down. The pressure is at the recommended level (33 psi). I went back to complain to Costco the next day that they broke or installed something wrong but they said they weren't mechanics and that the TPMS system on my car was not an air sensor in the tire but one that checked while braking what was happening to the wheel. I called his bluff because I know the TPMS alert went off while I was at a stop light. I was stopped behind several cars at the light so I reset it and it went off 2 minutes later before I STARTED MOVING so no braking was involved. He still went back to telling me to go to the dealership or mechanic to look at the TPMS system. So back to my original question: why would a TPMS alert go off after replacing tires? Is it because the tires are new and the computer inside the car needs to recalibrate to the spinning of the new tires? Did Costco break something and are just making things up hoping I won't use my head to figure out they are lying to get out of liability? Was the sensor on its last legs and just coincidentally broke at the same time the tires were replaced? | Short answer, you can not. Your car is equipped with an immobilizer. With out a properly coded key/transponder chip you will not be able to start your car. It disables fuel and spark. Its possible you could get the immobilizer tuned out of your ecu but this is much more complicated and expensive so not worth mentioning plus you would still need a key to unlock the steering. Your cheapest method will be to get a key from dealer with your registration and photo ID, then program the transponder yourself. Your easiest option is to call a mobile reputable locksmith to come out and generate a new key and program it for you. | {
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83,487 | I noticed While driving my car the fuel refills last me a lot longer when I go for the full tank over the half tank. I feel that it takes a lot longer to go through the upper half of the tank than the bottom half of the tank. I felt that keeping a full tank of gas is beneficial over the long run. Does having air in the tank reduce the burning efficiency?
Does keeping the tank full make the burning more efficient?. | No. If anything you'll get worse gas mileage with a full tank because you're carrying a heavier load (more fuel = more weight). What you are most likely experiencing is the top half of the tank is larger than the bottom half (in general terms). In other words, the sending unit (float level) in the gas tank most likely takes longer to traverse the top 1/2 then it does to traverse the bottom 1/2. This would make it appear you are getting better gas mileage on the top, because there is more gas in that top 1/2 than there is in the bottom. EDIT: Criggie said in comments what I was trying to point out. When I say "top 1/2" and "bottom 1/2", I'm talking about what the gauge is reading. Not the actual 1/2 of the tank itself. This is in direct comment to what Fake Name stated about being nitpicky, as they are exactly right. | {
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83,690 | This is for a 2018 VW Tiguan Allspace with 49,000 km (34500 miles). Living in a pretty mild climate (ie no snow and no extreme heat), but near the coast. The pad wear light came on and I scheduled the service with the dealer. I got a call later to say that the rotors should be replaced and they always recommend replacing the rotors with the pads because "European Cars use softer metals in their rotors". I would completely agree with replacing the rotors if: The rotors had scoring, rust etc on their faces The rotors were warped The rotors were at minimum thickness. The rotor on one side was needed replacement (in this case I think you should do both) I thought that the whole purpose of pads is that they take the bulk of the wear, and then you replace them more frequently than the rotors (and calipers). Theoretically I think it would require less time to replace just pads (seems that way in motor racing). I guess I would expect to replace rotors, which have none of the issues in the above list, maybe every second pad replacement. We do occasionally tow a 1500kg caravan, but I would expect this to create higher wear on the pads. If the reason hadn't been "European Cars use softer metals in their rotors", I probably wouldn't be asking questions. Also, if the rotors have no visible damage, when you replace pads, why would any resurfacing be required. Surely the new pads will bed into the existing rotors after 100km (60 miles) or so. Appreciate any thoughts. Cheers | You are right to be skeptical, the 'softer metals in european rotors' is complete horsedung. A bit of rust is completely normal, the rest of your criteria for replacing rotors is right on the money, if the dealership is trying to pull that line on you then they are either incompetent or trying to run up your bill. | {
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83,693 | We were on vacation and was stuck in traffic. Once traffic cleared we picked up speed and stopped at a light. After that that’s when it happened. The Tahoe would shift into 2nd and just rev up. Changed to solenoids A and B also changed the filter in the transmission. Did the same thing had to have it towed home. I let it sit in the yard for a bit then replaced the transmission. Put atf in it but wasn’t enough. Added a bit more that day and drove it home. The next day it was raining so I didn’t mess with it. Then my fiancé drove the Tahoe and to Walmart and back and unloaded groceries. Went back outside to crank the car and drove it on the road and that’s when it did the same thing. So far I have changed throttle position sensor. 02 sensor. Cause it threw those codes. If anyone could help please let me know | You are right to be skeptical, the 'softer metals in european rotors' is complete horsedung. A bit of rust is completely normal, the rest of your criteria for replacing rotors is right on the money, if the dealership is trying to pull that line on you then they are either incompetent or trying to run up your bill. | {
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85,061 | Where I live, it is common for car mechanics to help their customers who are planning to purchase a new used car by performing an OBD2 diagnostic test on the car in question, even if there are no dashboard warning lights. What is the point of this? According to my understanding, if the vehicle’s self-diagnostic and reporting capability has detected an issue, it will show a warning light on the dashboard. Then, the OBD scan would be used to get the specific diagnostic trouble code for the issue. I know that it is possible to mess with a vehicle and disable the dashboard warning lights. However, in that case, the lights do not come on when turning on the ignition, so I assume that this is easy to tell. | In most cases, unless things have been cleared, there's a good chance that if there was an issue previously, the codes will still be present in the ECU. Some codes are permanent (well, semi-quasi-permanent ... there are ways to get rid of them, but not for the "average" person), so will stay in the ECU. If a problem is intermittent it could cause the light to come on, which which would cause a code to appear in the ECU, but the light will go away during a "good" period. In this case the code won't go away unless there is manual intervention. No light on the dash, but the code would still be there. This can provide a clue as to whether there's an underlying issue which may need to be fixed. Another thing which the mechanic could check for is if the codes have been recently erased. If there's a problem which isn't shown except when the drive cycle is finished, you can temporarily get rid of a CEL by clearing the codes. It then takes some time for the drive cycle to complete (some cars longer and some cars shorter). You can look at the scanner and tell what the status of the drive cycle is, and therefore can see if there might be an issue which isn't reported under by a CEL. | {
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85,066 | I would like to know the following information. 1 By Default, a Car Automobile is manufactured as Left hand or Right hand drive. In terms of engineering efforts, how easy or difficult is the transition from Left hand to Right hand drive and vice versa? I mean the existing Car with Left Hand drive is changed to Right Hand drive and vice versa without purchasing a new vehicle. What will be the engineering efforts in terms of mechanical/electrical parts changes? 2 Are there countries which offer both Left hand and Right hand drive vehicles? | In most cases, unless things have been cleared, there's a good chance that if there was an issue previously, the codes will still be present in the ECU. Some codes are permanent (well, semi-quasi-permanent ... there are ways to get rid of them, but not for the "average" person), so will stay in the ECU. If a problem is intermittent it could cause the light to come on, which which would cause a code to appear in the ECU, but the light will go away during a "good" period. In this case the code won't go away unless there is manual intervention. No light on the dash, but the code would still be there. This can provide a clue as to whether there's an underlying issue which may need to be fixed. Another thing which the mechanic could check for is if the codes have been recently erased. If there's a problem which isn't shown except when the drive cycle is finished, you can temporarily get rid of a CEL by clearing the codes. It then takes some time for the drive cycle to complete (some cars longer and some cars shorter). You can look at the scanner and tell what the status of the drive cycle is, and therefore can see if there might be an issue which isn't reported under by a CEL. | {
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85,128 | After raising a car for inspection, I noticed that a mechanic gave all 4 wheels a spin. What exactly are they looking for? I assume it has to do with whether the wheel on the opposite side will spin as well? Or is it more about listening for any strange sounds? Is it related to wheel flanges or bearings? | Probably a combination of things - as you surmise, it's a good way to check for worn bearings (you may also spot them rocking the wheel up and down or side to side, that's also checking the wheel bearings). Spinning them can also show up a binding brake (as the wheel will be hard to spin), or a problem with the drive train, such as a knocking CV joint on a front wheel drive. You should also see them lift each wheel with a tool that looks a bit like a pry bar, that will be checking the suspension bushes for excess play. | {
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85,611 | Recently I had to get the catalytic converter in my automobile replaced because it was stolen. The repair shop said that to do it properly, and have the engine light go off, they have to use a more expensive catalytic converter. Why are cars designed like this when it is just a simple filtration system? Is there a car designed specifically for the cheap catalytic converter in mind? | It is not a simple filtration system. It is, as the name implies, a catalyst system. In order to work properly, the catalyst must be maintained in the correct condition, which means, being fed the right amount of oxygen relative to fuel. To know how much that is, the engine computer needs sensors in the cat. It then adjusts engine injection parameters to hit that number. Without those sensors, the cat just won't work. What is a cat doing with oxygen? Two different things. First, it wants a lack of oxygen (rich mixture) so it can reduce nitrogen oxides to nitrogen. Then it wants an excess of oxygen (lean mixture) so it can oxidize carbon, unburned hydrocarbons and carbon monoxide into CO2. Now if you have one of those 80's cars, you have two separate catalyst beds. The engine is run intentionally rich, so the first catalyst bed can reduce nitrogen oxides. Fresh air is then injected, so the second bed can oxidize the hydrocarbons. The fresh air comes typically from a belt driven air pump. In newer cats, they eliminate the air pump by using a cat with a heck of a trick: it stores oxygen momentarily. However, the computer must wobble the exhaust very precisely between rich and lean, in the right amount and timing to keep the cat stocked but not overwhelmed with oxygen. It may also help the computer to know the temperature of the cat. So that's why you need sensors on a catalytic converter. Have your exhaust shop bolt on a plate of expanded steel mesh across the cat. The cat thief will most likely just leave and steal another car's cat. Thieves don't like variables. | {
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85,615 | I am attempting to matriculate my camper from the UK to portugal and in order to do so they have requested what is known as a "certificate of conformity". Unfortunately i cant get one of these because the vehicle was manufactured prior to Jan 1995 and is also originally a japanese import. Instead they are now asking for the following information; Cylinder/Displacement Type of CO2 tests (WLTP OR NEDC) CO2 gas emission (g/km) Particles (More OR Less than 0,001 g/km*) I am really struggling to find this and when i spoke to Toyota UK they told me to contact Toyota Japan so I have hit a dead-end. Is this information readily available anywhere? | It is not a simple filtration system. It is, as the name implies, a catalyst system. In order to work properly, the catalyst must be maintained in the correct condition, which means, being fed the right amount of oxygen relative to fuel. To know how much that is, the engine computer needs sensors in the cat. It then adjusts engine injection parameters to hit that number. Without those sensors, the cat just won't work. What is a cat doing with oxygen? Two different things. First, it wants a lack of oxygen (rich mixture) so it can reduce nitrogen oxides to nitrogen. Then it wants an excess of oxygen (lean mixture) so it can oxidize carbon, unburned hydrocarbons and carbon monoxide into CO2. Now if you have one of those 80's cars, you have two separate catalyst beds. The engine is run intentionally rich, so the first catalyst bed can reduce nitrogen oxides. Fresh air is then injected, so the second bed can oxidize the hydrocarbons. The fresh air comes typically from a belt driven air pump. In newer cats, they eliminate the air pump by using a cat with a heck of a trick: it stores oxygen momentarily. However, the computer must wobble the exhaust very precisely between rich and lean, in the right amount and timing to keep the cat stocked but not overwhelmed with oxygen. It may also help the computer to know the temperature of the cat. So that's why you need sensors on a catalytic converter. Have your exhaust shop bolt on a plate of expanded steel mesh across the cat. The cat thief will most likely just leave and steal another car's cat. Thieves don't like variables. | {
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85,973 | I recently bought a KTM Adventure 390. When I start the bike in neutral and then shift to first gear, the bike moves(jerks) forward a little, even though the clutch lever is still pulled all the way. Is this normal? | This is common among all motorcycles that have a "wet" clutch system. What that means is that the clutch is surrounded by fluid, usually engine oil. Even though you have the clutch pulled in which disconnects the clutch plates, there is still oil surrounding both the input and the output parts of the clutch. So there is some rotation from the engine being transferred to the input shaft of the transmission gears and this causes the "jump" you experience when you go from N to 1st. The technical term for this effect is called "viscous coupling". Motorcycles that have a "dry" clutch such as some Ducati models, don't do this as there is just air which doesn't transfer enough rotational force to create the same effect. Bottom line is that this is entirely normal and it's not a problem that needs to be corrected. | {
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85,986 | I checked that car service checks many different parts like engine oil, filters, lights, brake, etc. I would assume they will tell you if something is not working. But will I be told also why something is not working? i.e. should I also expect them to diagnose the problem? For example, say it is quite obvious that my tail lights do not light up, if I bring my car in for service, besides being told what I already know, will they also try to find out why the lights are not working (fuse, bulb, wire, socket, switch, software, etc.) as part of the service? Or diagnosing is always something extra? | This is common among all motorcycles that have a "wet" clutch system. What that means is that the clutch is surrounded by fluid, usually engine oil. Even though you have the clutch pulled in which disconnects the clutch plates, there is still oil surrounding both the input and the output parts of the clutch. So there is some rotation from the engine being transferred to the input shaft of the transmission gears and this causes the "jump" you experience when you go from N to 1st. The technical term for this effect is called "viscous coupling". Motorcycles that have a "dry" clutch such as some Ducati models, don't do this as there is just air which doesn't transfer enough rotational force to create the same effect. Bottom line is that this is entirely normal and it's not a problem that needs to be corrected. | {
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85,993 | I may or may not be overthinking. I'm new to motorcycles and I bought a new motorcycle. Here's the full thing: So we don't have a showroom in my city. So someone I knew rode it personally to deliver it to me. I was with him as a pillion. The motorcycle is 110 cc and at some points he rode at the speed of 62 kmph. The max speed of this motorcycle is 87 kmph. We never tried to go near max speed anyway. It's NOT like he always rode at 62 kmph. I would say average speed was around 40 kmph. We rode 40 Kms in 1 hour and reached home without any problems. The rider is very experienced with low cc commute motorcycles. Now, I came across some questions and answers on Quora which say you should ride a new motorcycle like this at slow speed... for first 1000 Kms. They gave example that if it's less than 150 cc motorcycle, ride at around 40 kmph max. But as you know, at some points we rode it at 62 kmph. Then I checked my owner's manual and it doesn't mention anything specific speed limit. It just says: Running-in Period During the first 500 km (300 miles) of running, follow these guidelines to ensure your vehicle’s future reliability and performance Avoid full-throttle starts and rapid acceleration. Avoid hard braking and rapid down-shifts. Ride conservatively. I can surely say that the rider didn't do the max speed and didn't do high speed instant braking. But I'm a bit disappointed as we rode it at 62 Kmps for a few Kms. Then someone told me that if you're worried so much, you should change the oil as it will remove the dissolved or wear and tear "impurities". But again, I'm not sure if it's really necessary before 500 Kms for this commuter motorcycle. I'm not sure if it was really a big issue or I'm just overthinking. So given all that, can this slight "overspeed" during my first 40 Kilometers ride cause future performance issues with engine? If yes, should I change engine oil to avoid that possibility? | When it comes to running procedures the guidance in the owners manual overrides generalized advice on the internet. If the manufacturer intended for there to be speed restriction (or more likely an engine RPM one since engine speed is what matters not road speed) during running in they'd specify it there. From how you describe your friend's riding it seems pretty much in-line with what the manual suggests, so I really don't think you have anything to worry about. Also the whole journey was only 42km - short of bouncing it off the rev-limiter the whole way it's going to be difficult to do any serious wear to the engine in that short a distance. should I change engine oil to avoid that possibility? No - change the oil when the manual tells you the first one is due and not before. Some engines will be supplied with oil specific for running in and you actually risk doing more harm than good by prematurely changing it to the "normal" oil. Keep following the manual's guidance and enjoy your new bike! | {
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86,192 | My largest car maintenance cost is exhaust pipes, mostly catalytic converters. I do not think this is the case for most people. What am I doing wrong? I tend to buy cheap cars (<£500), change the oil myself, get the brakes changed when they squeak and change the car if there are any repairs that cost more than the car. I do not drive slowly, such that I am not surprised that I get through tires and brakes a little quicker than other people. However by far my largest maintenance cost is exhaust pipes (mainly catalytic converters). It is always the connecting pipes that corrode and/or break, rather than the actual catalytic element. I do not see an obvious link between driving style and exhaust pipe corrosion, and I am not aware of any preventative maintenance that could affect the exhaust pipe. On one occasion I went through three in the course of 4 years on the same car, and in two of those cases there was very little corrosion, the pipe sheared above the catalytic converter. I live in the UK, but not near the sea. Is there something I can do to make my exhaust pipes last longer? | Another cause of rapid exhaust system rusting is driving patterns which don't warm up the vehicle thoroughly. In this case, a "thorough" warmup means the entire exhaust is hot enough to cause all moisture within to evaporate. Depending upon the vehicle, this might take 10 miles of driving, the sort of distance necessary to warm the oil (not the coolant) to a steady temperature. If the vehicle is driven a lesser amount, moisture will remain in the system, and its presence will accelerate corrosion. | {
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87,601 | When using a Volkswagen Passat 2014 and going backward, I notice that the backup camera turn off when I start gaining speed (over > ~30 km/h). How can I prevent the backup camera from turning off? | It's set in the ECU in the "Park/Steer Assist" module and controlled by an adaption channel called "Switch-off speed for parking assist" IIRC and you can change the value there (ironically jwh20 was correct in their initial guess - it's usually 15kph from the factory), the value has both lower and upper bounds that you can't go beyond (5kph -> 20kph). This isn't something you can access through a menu in the car itself - if you want to change it you need something like VCDS, OBDeleven or Carista. I seriously doubt those upper and lower bounds can be changed without some seriously major effort changing the firmware - and while 20kph might not sound like much, but firstly driving in reverse at speed is a bad idea in general, and trying to do it from a reversing camera view in lieu of a actually looking behind you is heading towards just plain dangerous. | {
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87,844 | Yesterday car suddenly didn't start. We boosted it and drove for an hour. When parked, it would restart immediately. But after waiting 1 minute, it wouldn't start again. Today I measured the battery:
After being parked overnight: 10V
When car running after boost: 14.5V
When car turned off after less than 5 minutes running: 12,5V
2 minutes later, back to 10V again. I did not understand how it could go from 10V to 12.5V after less than 5 min charging by alternator. Second time I tried, after turning off the car I could literally see on the multimeter the voltage dropping rapidly from 12.5 down to 10 within a minute or two. Can this be caused by anything other than a bad battery? | Nope. That pretty much sounds like a dead battery. It sounds as though one of the cells has a short in it, which is causing your rapid voltage decrease. There's no way to fix this other than battery replacement. Since it does run at 14.5vdc during engine operation, that means the alternator is doing its thing and attempting to charge the battery. | {
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88,927 | I am not sure if if this is the right forum to ask this, but even my driving instructor cannot give me a clear answer, hence the question.
Learning driving on a toyota vios, automatic transmission. The interrelated questions I have are Does the accelerator control and ensure gas is flowing through the engine? The harder I press, the more gas flows in and the faster is the engine RPM. Is my mental model correct? Also, if this is the case, does it mean unless I step on the accelerator, no gas flows in and the engine does not spin (unless it was spinning, because of inertia)? While driving at, suppose 50kmph, suppose I take my foot off the accelerator, and neither do I press the brake. Does it mean the engine will still spin for sometime (because of inertia) and the car will move some distance (may be even a few miles) before eventually coming to a halt? Is it like when I stop pedaling when riding a bicycle? What happens if I press both the accelerator and foot brake together? As one tries to move the car, and another resists, will some parts internally grind against each other, eventually damaging the parts, maybe even an accident? Do not want to try this, just want to know what happens in that case. Or is the car somehow smart enough to not let the engine spin when the foot brake is pressed? Does pressing the foot brake, in automatic, also decouple the transmission (wheels) from the engine, in addition to resist the wheel with brake shoes? Is it similar to neutral in manual? | In short, find a better driving instructor and, if possible, learn to drive a car with manual transmission. The long (still simplified) answer: Does the accelerator control and ensure gas is flowing through the engine? The harder I press, the more gas flows in and the faster is the engine RPM. Is my mental model correct? Also, if this is the case, does it mean unless I step on the accelerator, no gas flows in and the engine does not spin (unless it was spinning, because of inertia)? Generally, yes, but there are other factors that affect the amount of fuel allowed in the engine: Idle. When the engine is turned on, some fuel is allowed in the engine even with the accelerator pedal fully released. This is why automatic cars inch forward when the transmission is in "D" position. You need to apply brakes to prevent this. This is also how e.g. steering assistance or air conditioning are powered. The actual amount of fuel depends also on the engine RPM at the moment. Other, less important factors also impact the engine fuel consumption/power. While driving at, suppose 50kmph, suppose I take my foot off the accelerator, and neither do I press the brake. Does it mean the engine will still spin for sometime (because of inertia) and the car will move some distance (may be even a few miles) before eventually coming to a halt? Is it like when I stop pedaling when riding a bicycle? Mostly. An automatic car will not, in fact, completely come to a halt on a level road - see about the "idle mode" above. Slopes can alter this behavior. Uphill, the idle engine power may not be enough to creep the car forward. Downhill, the car can gradually accelerate all the way to its designed maximum speed (and even more) with no action on the accelerator pedal. It is up to the driver to apply brakes and common sense. What happens if I press both the accelerator and foot brake together? As one tries to move the car, and another resists, will some parts internally grind against each other, eventually damaging the parts, maybe even an accident? Do not want to try this, just want to know what happens in that case. Or is the car somehow smart enough to not let the engine spin when the foot brake is pressed? In a sane car, brakes outpower the powertrain by a great margin. If you press on brakes strong enough, no pressure on the accelerator pedal will make the car move. Don't really try this, a wrong order of releasing the pedals can make you car vigorously jump forward, up to and including crashing into some obstacle. Yes, if you insist on pressing and holding the accelerator and the brakes together, some parts wear intensively and can overheat in a few minutes. Repairs will be expensive. This (among other things) is why automatic cars are controlled by a single foot and this is one of the first things you learn in the driving lessons. Then again, pressing both pedals (to an extent) is sometimes used when driving off-road. Does pressing the foot brake, in automatic, also decouple the transmission (wheels) from the engine, in addition to resist the wheel with brake shoes? Is it similar to neutral in manual? Not really. An automatic transmission always applies some torque to the wheels. If the accelerator is not pressed, the internal friction that applies this basic torque is considered safe. You are not expected to manually disengage the transmission when waiting for a green light. If you really want to disconnect the transmission, there is "N" position on most automatic transmissions. "P" is the same, but it also applies an internal brake mechanism that blocks the wheels. | {
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88,934 | I have a Husqvarna 45 chainsaw and it won't start only if the trigger is pulled, and if i release it , the chainsaw stop's. Any suggestions? | In short, find a better driving instructor and, if possible, learn to drive a car with manual transmission. The long (still simplified) answer: Does the accelerator control and ensure gas is flowing through the engine? The harder I press, the more gas flows in and the faster is the engine RPM. Is my mental model correct? Also, if this is the case, does it mean unless I step on the accelerator, no gas flows in and the engine does not spin (unless it was spinning, because of inertia)? Generally, yes, but there are other factors that affect the amount of fuel allowed in the engine: Idle. When the engine is turned on, some fuel is allowed in the engine even with the accelerator pedal fully released. This is why automatic cars inch forward when the transmission is in "D" position. You need to apply brakes to prevent this. This is also how e.g. steering assistance or air conditioning are powered. The actual amount of fuel depends also on the engine RPM at the moment. Other, less important factors also impact the engine fuel consumption/power. While driving at, suppose 50kmph, suppose I take my foot off the accelerator, and neither do I press the brake. Does it mean the engine will still spin for sometime (because of inertia) and the car will move some distance (may be even a few miles) before eventually coming to a halt? Is it like when I stop pedaling when riding a bicycle? Mostly. An automatic car will not, in fact, completely come to a halt on a level road - see about the "idle mode" above. Slopes can alter this behavior. Uphill, the idle engine power may not be enough to creep the car forward. Downhill, the car can gradually accelerate all the way to its designed maximum speed (and even more) with no action on the accelerator pedal. It is up to the driver to apply brakes and common sense. What happens if I press both the accelerator and foot brake together? As one tries to move the car, and another resists, will some parts internally grind against each other, eventually damaging the parts, maybe even an accident? Do not want to try this, just want to know what happens in that case. Or is the car somehow smart enough to not let the engine spin when the foot brake is pressed? In a sane car, brakes outpower the powertrain by a great margin. If you press on brakes strong enough, no pressure on the accelerator pedal will make the car move. Don't really try this, a wrong order of releasing the pedals can make you car vigorously jump forward, up to and including crashing into some obstacle. Yes, if you insist on pressing and holding the accelerator and the brakes together, some parts wear intensively and can overheat in a few minutes. Repairs will be expensive. This (among other things) is why automatic cars are controlled by a single foot and this is one of the first things you learn in the driving lessons. Then again, pressing both pedals (to an extent) is sometimes used when driving off-road. Does pressing the foot brake, in automatic, also decouple the transmission (wheels) from the engine, in addition to resist the wheel with brake shoes? Is it similar to neutral in manual? Not really. An automatic transmission always applies some torque to the wheels. If the accelerator is not pressed, the internal friction that applies this basic torque is considered safe. You are not expected to manually disengage the transmission when waiting for a green light. If you really want to disconnect the transmission, there is "N" position on most automatic transmissions. "P" is the same, but it also applies an internal brake mechanism that blocks the wheels. | {
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89,034 | I have a Land Cruiser 2010. It's the third time this is happening. Any USB stick that's connected to the Audio USB/AUX port gets super hot and stops working after a few seconds. Yesterday I connected a bluetooth receiver in this port as well and it was killed the same way. I'm sure this USB port is for music and not charging as its right next to the AUX port. Any idea why this is happening and how I can prevent it? | The port is badly broken, stop using it until you get it fixed. If it has always been like this, chances are the port is miswired so that the +5V and ground pins are swapped (perhaps an internal cable plugged in the wrong way round). The reverse polarity would almost certainly destroy any devices plugged in (there's no way to plug in any USB connector the wrong way round, so this is not a risk that device designers would normally protect against). On the other hand, if the port used to work normally and then started doing this all of a sudden, it's fairly likely the USB hub powering the port is toast and its 5V regulator is potentially letting full 12V+ through. Such an excess voltage will likely fry any unsuspecting device. The only solution would be to have the USB hub inspected and replaced. (Which might entail replacing the whole entertainment system or something, I'm not familiar with the car.) | {
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89,531 | In my country of residence (developing nation) I sometimes see people stopped alongside the road because they apparently forgot to buy fuel or couldn't afford it. I also would like to be able to push a bit further on my motorbike since the fuel light comes on pretty early. For those purposes I'd like to bring a TINY amount of gasoline with me on the motorbike, in the under-seat compartment. My motorbike does 40 km on a liter so if I bring 200 ML it should be more than enough to reach a gas station. I can just empty it out in my gas tank every month or so, and refresh it, so longevity shouldn't be too much of a problem. Now I know I shouldn't be storing fuel in inappropriate containers, so what would a decent solution for this be? I cannot find jerry cans of such a tiny size. Glass is not recommended for fuel, but would it matter for a small amount, if not filled to the top? And would a glass jar not leak? | You can use a camping fuel bottle . They are usually made of aluminum, they are made to hold flammable liquids including gasoline, and they do not leak. I have seen them as small as 500 ml, and you might find a smaller model if you search. | {
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89,556 | I made a big mistake today attempting to jump start a car but connected negative clamp (-) to wrong part of the car. Basically there was no negative connection between the two cars. I did not notice until later because the jump start actually did work, and the car with the dead battery started to run again and we got the battery replaced. But I noticed small electrical problems on both cars after the jump start. First of all, I do not understand how the jump start worked with only positive + connection, and I worry because I am not sure if it is safe to drive either car. I cannot assess how much harm the jump start did to both cars. Should I bring in to the repair shop? The feeder car was 2018 BMW X1 and the empty car was 2015 Nissan Murano. The green circle was where I connected ‘live’ negative cable. The other end on a bolt in ‘dead’ car. (Ground) Electrical problems for X1 now I notice include Seat position memory gone (which I could reprogram), and radio channel showing differently on screen. (When I select 1, it will show 2 on screen) Those are minor so I am not worried, but I just don’t know if there were any more damages done to the car that I do not know yet. | You can use a camping fuel bottle . They are usually made of aluminum, they are made to hold flammable liquids including gasoline, and they do not leak. I have seen them as small as 500 ml, and you might find a smaller model if you search. | {
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89,563 | SOLUTION: The tubes on the top of the motor for the PCV system were backwards. See https://invidious.fdn.fr/watch?v=07ssRI8k81E for correct configuration. Oil would pool in the air intake until you drove it up hill, and then it would start to enter the engine and burn off. Original: Does substantially increased compression test numbers after adding oil to the cylinder necessarily imply that piston rings and/or cylinder bore is bad? My 2003 Toyota Matrix (1zzfe) is burning oil and blowing smoke. I did a compression test and the numbers seemed low, after putting a bit of oil in the cylinder and re-testing compression improved substantially (about 30 PSI). After dismantling the motor I used a micrometer to check the cylinder and it looked OK to me, across each entire cylinder there might have been about .001" difference. I honed the cylinder and put in new rings. Put it back together, and its still burning oil. So I redid the compression test with nearly identical results. Compression across all cylinders is roughly identical.
60 PSI on first bump, ending around 150 PSI.
With oil, 90 PSI on first bump, ending around 175 PSI. Do these compression test results necessarily mean that its piston rings and/or cylinder bore? Given than I just put in new rings then with would have to be the cylinder bore in this case. However because the pressure is identical across cylinders, and given I mic'd, honed, and put in new rings, I'm inclined to believe that the oil burning problems are related to valves and my compression numbers are actually OK. For reference, my compression test instructions: | You can use a camping fuel bottle . They are usually made of aluminum, they are made to hold flammable liquids including gasoline, and they do not leak. I have seen them as small as 500 ml, and you might find a smaller model if you search. | {
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89,895 | While there are exceptions the majority of cars use fuses instead of circuit breakers to protect electronics and I'm wondering why circuit breakers are not more widely used. Is it practicality, cost, regulations or a combination of those factors? | (1) Fuses are cheap. Really cheap. You can get a variety pack of 100 for $8 or so. Circuit breakers for 12V systems are available, but are not cheap (more like $10 each). My car has 40 or 50 circuits, so that is a large chunk of change. (2) Fuses are small and can be put into tight spaces, much smaller than you can get your fingers into. Look at your main fuse box and consider just how large it would get with breakers, even the push-button ones. (3) Breakers are great for circuits you want to turn off, or quickly turn back on. But neither of those really comes into play on a car - 12V won't kill you, unlike your house wiring. (4) Mostly your car just runs. In 45 years of driving I've never replaced a fuse. (5) Circuit breakers have mechanical parts that need to move when needed, and not move when not needed. Cars experience shock and vibration through their lifetime, making the simple fuse a more reliable way to protect a circuit. (6) from @Criggie, particularly in the engine bay there is oil, dust, water, etc. Fuses don't notice, many breakers will not like that. You can get marine grade breakers that are sealed, but that adds cost. | {
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11 | At the risk of being too venal: yesterday I had over 8500 and now I am under 7900. Anyone else experienced changes with similar orders of magnitude? | Upvotes on questions now only contribute +5, rather than the original +10. There are a number of other changes, but this explains the bulk. | {
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577 | On SE and on the old MO have seen @someone in a question. Probably this notifies someone in his inbox and draws
his attention (which is the goal). Does it really notifies in a question? Is this good practice? My concern is it might be considered spam by some,
yet others might like it in case the question is interesting. | @notifications only work in comments, and then only if the target user is either the owner of the post you're commenting on, has edited or closed that post or has commented on that post. You can only use @notifications to respond to a user directly, not to notify them in a different question they have never interacted with. I personally would avoid using such inactive notifications in posts as they tend to confuse new users who might get the impression that those actually work and notify users. | {
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617 | This is a place to collect MathOverflow success stories! Was some of your research inspired by something on MathOverflow? Do you know questions & answers that led to interesting research? MathOverflow citations? Open problems solved on MathOverflow? Then add your story in an answer! (One story per answer, please!) If you want to help get this thread started, you can use this search to find MathOverflow citations on the arXiv or migrate some old stories from tea.mathoverflow.net . | Mark Sapir solved an interesting open problem in group theory in this answer to a question of Narutaka OZAWA . | {
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882 | How do I write a good MathOverflow question? Got any advice for me? | Using MathOverflow should be an extension of the way you normally do mathematics, and the same rules you use to effectively solve problems can be used to make good MO questions. Just like solving problems, crafting good questions requires you to put in some effort! Ask a focused question that has a specific goal Be precise Do your homework Break it down Consider different formulations of the question Provide background and motivation Make your title your question Format your question well Additional resources Ask a focused question that has a specific goal It should be absolutely clear what constitutes an answer to your question. Here are some examples of vague and specific questions. For each one, ask yourself, "If I saw an answer to this question, could I confidently determine whether it tells the asker what she actually wants to know?" Too vague/broad What can I deduce from X? What is known about the X conjecture? What are all the ways to do X? Tell me about elliptic curves. Focused Does X imply Y? Is there an example of X such that Y? Is the X conjecture true in situation Y? Is there a way to do X other than Y (which I can't use because Z)? Note that being specific does not mean plugging in specific numbers or otherwise making your problem look like an exercise in a book. It means asking a to-the-point question that has an answer . If you can't turn your question into a specific one, ask yourself what you hope to gain by asking the question. What concrete goal are you moving towards? If you can't think of one, then please don't ask the question. If you just want to know more about some area, read a book or an article or the Wikipedia page or Google for it. Either you'll learn about the subject effortlessly, or at some point you'll get stuck on some very concrete thing. If the former happens, good for you! If the latter happens, then the MathOverflow community is here to help you get unstuck. If you have a concrete goal, but your question is extremely broad, break it down into more focused questions. Be precise Being precise means communicating the parameters of your question so that others know where to start answering it and know when they've given you a complete answer. Of course, the includes stating the hypotheses and goal of your problem. If you suspect that you're asking an elementary question outside of your field, you may also want to explain your background a bit. This makes it easier for the person answering your question to know what she can take for granted. It is especially important for "soft" questions and "big list" questions to be precise. Otherwise they'll be boring and useless. "What are the best number theory books" is a bad question. Best for what? Assuming what background? A better version of the question might be "What are the best textbooks for an undergraduate number theory course?" or "After an undergraduate number theory course, what should I learn if I want to study elliptic curve cryptography?" These questions aren't great, but they make it clear what the starting point is and what the goal is. Make sure it's clear exactly what your question is. It's extremely frustrating to read a long question which explains what the general problem is but doesn't contain an actual question. I usually resort to searching the body of the post for question marks, but it often doesn't help. After defining all your terms and motivating your question, consider visually distinguishing the final version of the question (see the formatting section). There are few things worse than a question which is too vague, too broad, or imprecise. Not only is it lazy to ask a vague or imprecise question, it's also rude. You're essentially asking somebody to do the work of figuring out what you want to ask, and then answer it, or to answer several possible interpretations of your question. Suppose somebody asks, "What do you guys think about Foobar's new paper?" Even if this is exactly in my field, and I understand Foobar's paper better than Foobar himself, I have no idea where to start answering a question like that. Compare to, "Does Foobar's regularization construction solve the Baz-Flipt Conjecture?" As an expert, this is something I can actually answer. When you're browsing MO, please don't vote up unfocused or imprecise questions. Such questions are as bad as (or worse than) homework questions; they waste everybody's time. If somebody asks, "What's the deal with algebraic geometry?" you might say to yourself, "Wow, I'd really love to see a great answer to that one. I'm going to vote it up." But don't! You're encouraging the wrong behavior. The great answer you're hoping for doesn't exist because there isn't a precise question. At best, somebody will answer, "go read a survey article or a standard reference or the nLab page or the Wikipedia page." Worse, somebody who is too kind and too generous with her time may spend a great deal of time and energy crafting an answer that might not satisfy the asker and that will be just a shadow of a proper survey paper. Such questions can't be reasonably answered in a few hours, even by an expert who knows the "answer." Do your homework Before asking your question, try to solve it. Search Google , Wikipedia , and nLab , check any references you can think of, and try to figure the problem out yourself (maybe even sleep on it). Doing so will help you break the problem down and understand it better. Even if you don't solve the problem, putting some work into it will often help you understand exactly what it is you're having trouble with, so you'll be able to ask a better question. Break it down You may have a specific problem you're trying to solve, and you may have done your research, but the problem might be a monster. Even if it's not a monster, you'll probably benefit from trying to break the problem into smaller pieces and posting one or two of the pieces on MO. To modify a quotation of Pólya, "If there is a problem you can't solve, then there is an easier problem you can't solve: find it." You may worry that the the pieces are not interesting enough or are too specific to post on MathOverflow, but you shouldn't. It's much better to post a question that is too focused than to post a question that is too vague or too broad. It's okay to ask several questions related to a project you're working on, but try to limit yourself to one or two per day. Rather than posting all the parts of your problem at the same time, work through them one at a time. After all, the solution to one part may completely change your plan for solving the problem. Consider different formulations of the question Sometimes your question is boring, but you can often make it much more interesting by recontextualizing it. It could be enough to just ask if your question is false. For example, you might be reading a book when you come across "Theorem 2.1. Every regular doodad is a widgit." You read the proof, but you don't understand where it uses the hypothesis that the doodad is regular. Your question is "Where does the author of this book use the regularity hypothesis in Theorem 2.1?" That is a boring question! But answering it is equivalent to answering an interesting question, "Is every doodad a widgit?" That is, does the result remain true if you remove (or weaken) the hypothesis? Ask the more interesting question, and add "I ask because I'm reading the proof of Theorem 2.1 of this book, which shows that regular doodads are widgits, but it looks like it doesn't use the regularity hypothesis." Another thing you could try is to broaden the appeal of your question by generalizing it. Generalizing is actually a way of breaking the question down, since it amounts to removing hypotheses. For example, you might be trying to prove that some particular object X is a widgit. Asking "Is X a widgit?" might not be a very interesting question. So you do your homework by looking for references and by trying to prove it in various ways. Eventually, you realize that the basic property of X that should force it to be a widgit is that it is a doodad, so you ask yourself, "Is every doodad a widgit?" Of course not; it's easy to come up with doodads that aren't widgits. There must be some other property of X that will allow you to prove it's a widgit. Maybe it's because X is a regular doodad. After thinking about it for a while, you think that it's plausible that every regular doodad is a widgit. If you can't come up with a proof or a counterexample, then you could ask, "Is every regular doodad a widgit?" If you do, you may want to explain in a background/motivation section that you're really trying to show that X is a widgit. Provide background and motivation MathOverflow isn't just a place to ask and answer questions. It's also a place to read questions and answers, which is a great way to see what people in other fields think about, and to see how they actually think about it (not just what the polished papers look like). So when you ask for the help of those who know more than you, please also extend a hand to those who know less than you by explaining why you are asking the question. You'll get more votes, generate more interest, and are more likely to get your question answered. Explaining the motivation for a question may also help you gain a fresh outlook on the topic you're asking about. MO is meant to develop your ability to do mathematics, but also to develop your ability to communicate it. Make your title your question (But don't forget to restate it in the body!) Use your title to convey as much information about your question as possible. Since the tags already convey the general subject area of your question, the title should communicate the question itself as faithfully as possible. If necessary, leave out hypotheses in the title, and in the body of the question, explain why the question requires those hypotheses. Don't be afraid to make your question title long. Titles are allowed to be anywhere from 15 to 150 characters long. 140 characters (the length of a tweet) takes up about two full lines on the home page, so try to keep it less than that. But 140 characters is a lot longer than you might think. Too many people restrict themselves to 20 character titles. They're trying not to waste your time by making you read a long title, but they end up wasting more of your time because you have to actually open the question to see if it's interesting to you. Format your question well The readability of your question can often be greatly improved if you learn to use formatting commands , especially if your question ends up being quite long. Here is an example that contains a few good uses of the formatting commands: ## Background/Motivation A *doodad* is a thingumabob together with a sheaf of doohickies (which is usually called the *doo structure* on the doodad). A doodad is said to be *regular* if the sheaf of doohickies is regular. Intuitively, regularity makes a doodad "rigid" since information about the doo structure at a point can be translated into information about the doo structure at nearby points. A *widgit* is a whatsit which is flat (in the sense that its Plotsky curvature is zero). Showing that a space has a widgit on it is extremely useful because the flatness allows you to apply Foobar's gadget construction to prove many useful results about the space. ---- Based on the above intuition, it is natural to ask if every doodad is a widgit. However, the answer is clearly no, since a widgit is always regular, but [some example] is a non-regular doodad, so it is clear that we must impose a regularity hypothesis. > Is every regular doodad a widgit? Background/Motivation A doodad is a thingumabob together with a sheaf of doohickies (which is usually called the doo structure on the doodad). A doodad is said to be regular if the sheaf of doohickies is regular. Intuitively, regularity makes a doodad "rigid" since information about the doo structure at a point can be translated into information about the doo structure at nearby points. A widgit is a whatsit which is flat (in the sense that its Plotsky curvature is zero). Showing that a space has a widgit on it is extremely useful because the flatness allows you to apply Foobar's gadget construction to prove many useful results about the space. Based on the above intuition, it is natural to ask if every doodad is a widgit. However, the answer is clearly no, since a widgit is always regular, but [some example] is a non-regular doodad, so it is clear that we must impose a regularity hypothesis. Is every regular doodad a widgit? Notice that the background/motivation is clearly labelled with a section header and clearly delimited by the horizontal rule, making it easy for experts to know what to skip or skim. The words being defined are italicized. After the nuances about why the question introduces some hypotheses, the precise final question is visually distinguished in a blockquote, making it easy to know exactly what constitutes an answer to the question. A final note Not every piece of advice on this page may apply to your problem, and it may even occasionally happen that you can make your question better by violating some rule laid out on this page. As with any writing you do, it is important to know what the basic rules are. If you violate one of them, it should be a conscious choice and you should be doing it for a very good reason. Additional resources Eric Raymond's How To Ask Questions The Smart Way is directed at people looking to post problems to computer software/hardware forums, but much of the advice applies to asking questions on MathOverflow as well. User contributed content licensed under the Creative Commons Attribution-Share Alike 3.0 Unported License with attribution required. | {
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950 | Does Stack Exchange or MathOverflow own my posts? Can I reuse my posts elsewhere? Do I need to cite MathOverflow if I want to reuse my posts elsewhere? | You own all of your posts! You retain full copyrights and you can do anything you please with them. However, by posting on MathOverflow, you release your content under the terms of the Creative Commons Attribution-ShareAlike 4.0 (CC BY-SA 4.0) license. This license allows MathOverflow, Stack Exchange and others to use your content under specific terms. This is not an exclusive license. As the copyright owner, you may release your content to anyone under any terms you please, though such waivers do not revoke the CC BY-SA 4.0 license that you previously agreed to. | {
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1,042 | Does outgoing moderator Anton Geraschenko deserve our heartfelt thanks, or what? | I think the answer is ... yes. | {
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1,053 | I feel that MathOverflow is unique in the StackExchange network. There are features which we might want which might be unique to this site, and which might not be immediate feature requests or requests that StackExchange would want to implement globally or even locally. There isn't currently a repository for such ideas. I think that it would be useful to have a big list of feature requests and suggestions for some fantasy future MO 3.0, to serve as feedback data to MO and to SE, and to serve as an incubator for possible potential future feature suggestions. Having these voted up or down by users adds information, and comments on these are also useful. Big list: Please suggest features, and make specific suggestions, for things you would want to see on a fantasy future MO 3.0. These don't have to be immediately implementable or likely to be implemented. One fantasy request per answer, please. Please try to avoid duplicate answers. I'll start the ball rolling by inserting some sample answers. Please comment and vote up or down depending on whether these seem like good ideas to you, in the abstract. I think the longer this list is, the more informative it is. Note that posting an answer here is not the proper way to make a feature request. If the feature you want is possibly implementable now, post it as a separate meta-question with the tag feature-request . | [Implemented on Nov 13, 2019] Restore +10 reputation for questions. A good question might actually be more important than a good answer, in mathematics and in life. Having them count for less than answers decreases the relative motivation to write detailed and coherent questions, and I suspect that it lowers the overall quality of questions on MO. On Fantasy MO 3.0, I would return +10 reputation to questions. | {
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1,113 | My questions is whether there is a good reason to allow anonymous users in a site dedicated to research-level mathematics. In theory, most users of this site are professional mathematicians and graduate students. In practice, I'm not so sure. The amount of ill-posed questions, homework problems, or just plain nonsense that is periodically closed, but which nevertheless clutters the site, suggests there is a substantial number of other people who use MO. In my view anonymity poses a number of problems: We freely share ideas on this site and the mathematical conversations that take place in MO sometimes find their way to publications. It is one thing to say "the proof of this lemma was worked out in an MO conversation with name-lastname" than to say "the proof of this lemma was worked out in an MO conversation with Bullwinkle101". I actually have to do this in a paper I'm writing right now. I have not done any serious statistics, but it seems to me bad questions have been driving the good ones out for some time. It is easier to be nasty as an anonymous user. Sometimes good mathematicians ask or say dumb things (as mathematicians, else the statement is truly obvious). There is no need to hide this. Actually, I think it is BAD to hide this. As a "guild" we believe too much in our own mythology. If one takes a look at the first three or five pages of users ranked by "reputation" the number of anonymous users is propotionately very low and the
proportion increases sharply as the reputation decreases. This suggests the question: what sort of users does MO wish to have? Now, as a matter of principle, I think restricting access (to whatever) is not usually a good idea or, at the very least, has to be done intelligently. ArXiv has managed to do this nicely. In fact, if for a second we think
of anonymous postings in ArXiv by whoever has an internet access and an interest for mathematics, we see that it could not be the useful research tool that it is today. Thanks to all who answered this question or commented on it. I now see that there are some valid reasons to participate anonymously and that there are other or better ways to deal with some the issues raised in this question. | Here is a past discussion on pseudonyms from MO.1 days: http://mathoverflow.tqft.net/discussion/335/1/why-not-real-names/ . I think most of the arguments (pro or con) would still apply to MO.2. (This find is based on a quick google search, but I think there may have been more discussions. Please feel free to edit this answer if you find more.) Women have often reported very negative experiences posting under their real names, for a variety of reasons. This is touched upon here: http://mathoverflow.tqft.net/discussion/985/ . This alone seems to be a serious trump card in favor of allowing pseudonyms. And it's not just women: many people have had very unpleasant experiences posting under real names (again for various reasons); I believe their needs should be respected. (I say all this despite the fact that I much prefer interacting with someone who uses his/her real name: I might have the pleasure of meeting them some day, or I might want to cite them, or maybe even work with them on something, and so on.) User alvarezpaiva (whom I know btw as "JC" or Juan-Carlos, from grad school days) has made some very good points in support of strongly encouraging the use of real names, but disallowing pseudonyms I really can't get behind. Last point: my own impression is that the rise of questions unsuited for MO is more accurately explained by the merger into the StackExchange network than it is by usage of pseudonyms. Some interesting reading material, with graphs, can be found here: Has the switch to SE 2.0 increased the rate of low-level / inappropriate questions? | {
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1,191 | I have noticed that those of my questions with downvotes are exactly those beginning with the words "what is known about..." or "is anything known about...." For example: Stationary many subsets of $\kappa^+$ whose order type is a cardinal and whose intersection with $\kappa$ is an inaccessible cardinal Absoluteness of "$\kappa$-homogeneously Suslin" for sets of reals I will be the first to admit (well, technically the second to admit) that these two are not great questions, and I'm not here to complain about the downvotes. My question for meta: Is this "...known about..." wording is frowned upon in all cases, or only if the question is otherwise overly broad? | First, let me state that the downvotes on these examples are hard to justify and the following is not a criticism of these questions. That said, "what is known about" is a common premise for a "fishing expedition" (to borrow a legal term ). These questions should be discouraged since the only correct answer is an encyclopedic one, which imposes unnecessary burden on the community unless the context is very narrow. In general, fishing expeditions should be closed as "too broad", preferably with a suggestion to ask a more focused question. Though it is very possible to write a focused question starting with "what is known about", it is better practice to avoid this kind of formulation because of the associated stigma.
See how to write a good MathOverflow question for tips on how to get around this problem. | {
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1,311 | Q1: What is your view on the purpose, aims and benefits of MO? Q2: What are your specific aim, targets and benefits in participation at MO? | A2: I treat MO to some extent as a substitute for a large mathematics department with experts in all sorts of areas. My university is small compared to many, and with only a few specialised research groups, and I can't always find an expert to wander up to and talk ask about various things I need that are at arms length from what I know. | {
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1,338 | I have the impression, that there is no concensus among MO moderators about sharing knowledge on MO; the impression is based on quite contradictory reactions to offering to share such a knowledge, ranging from encouraging to share it, despite some skepticism about the correctness or practical applicability to discouriging doing so, based on speculations on the mathematical value of such an answer or, on speculations about the personal motivation for sharing knowledge. I had read the discussion related to Answering my own question and Appropriate Reaction to a Failed Reference Request on MO and thus felt encouraged to share my knowlegde, but wanted to present in a way that would be appropriate for MO ( Preferred Conciseness of Contributions ), which, besides one useful comment, only brought up severe objections against sharing my knowledge. My question is therefore, whether there is consensus at least among MO moderators about what is appropriate and in what form, when "pressing the button" for answering own questions or sharing knowledge? What should happen with speculative comments and answers that aim at discouraging answering one's own question or sharing knowledge? | I cannot speak for the moderators, but as far as I understand, you should
only ask a question on MO if you do not already know the answer. However it may still happen that some time later (be it days, weeks, months
or years -- this does not matter) you find an answer to your question yourself.
If nobody else has provided a satisfactory answer to your question
in the meantime, then it is considered good practice that you answer your own
question, to avoid other people wasting their time on telling you what you
already have found out by yourself. Another situation where "answering" your own question is considered good
practice is when other people have answered your question in the comments.
In this case you provide a CW (community wiki) answer summarizing the
relevant comments, in order to make it visible for everybody that your question
is already answered and to get it off the unanswered questions list. | {
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1,390 | I am a bit confused by the close reason for https://mathoverflow.net/questions/154235/minimum-l1-norm-may-not-obtain-the-sparsest-solution?noredirect=1#comment395410_154235 . It is an easy question that the reader could have solved by reading carefully the statements of the theorems, I agree, but it is nevertheless a question encountered while reading a research paper in mathematics. Hence I am unsure about the factual correctness of the statement "This question does not appear to be about research level mathematics within the scope defined in the help center." "Help center" here links to a page stating: What kind of questions can I ask here? MathOverflow's primary goal is for users to ask and answer research level math questions , the sorts of questions you come across when you're writing or reading articles or graduate level books. Of course, individual questions don't have to be worthy of an article, and they don't have to be about new mathematics. A typical example is, "Can this hypothesis in that theorem be relaxed in this way?" I think the main source of confusion here is that the closure reason "this question is not research-level maths" is used for two different reasons: this question is off-topic because it's not about maths --- for instance, it's about physics, or about vacuum cleaners. this question is a reasonable math question, but it's too easy for a professional mathematician. Maybe we need a closure reason that is a nice way to tell "too easy, sorry". Something like "this question could be readily answered using standard material for an undergraduate student in mathematics, and so it is not of interest here".
Or something better. There is also an additional reason of confusion in this policy: what is an easy question for a graduate student in, say, algebraic topology, could be a challenging one for a professional researcher in, say, PDEs. A professional mathematician studying topic X could come up with a perfectly reasonable question about topic Y which is "standard" for someone using it, but yet not so easy that it is "undergraduate material". This is material that would be considered "too easy" at a conference on topic Y, but not if you ask another mathematician. Are these kind of questions on-topic? I see many questions of this kind on MO. I suspect that even more of them are so, for an expert in the suitable field, and it's just that I cannot recognize them as such. In my point of view, this is often the kind of questions that I want to use MO for. It saves me the hassle of locating in person an expert on topic Y (which my university could not have) and going to his room to ask. On the other hand, I could see an argument also for banning this kind of "reference-request" questions. If it's something that you could have answered simply by locating a researcher in algebraic topology, any researcher, why are you bothering an entire online forum which includes several Fields medalists? What would be left? Questions that are really "research-level", as in: they would not be trivial even for an audience comprised entirely of experts in the field. This would reduce a lot the traffic here, and also sectorialize it a lot. Everyone would understand only a very small subset of the questions. Many more questions would be closed. Actually, this criterion would sound very close to "if I you answer it, then close it instead of answering it". There are two overlapping questions maybe, one about the closing reasons, and one on MO's policies on what is to close. I am sorry, but I find it difficult to split this up into two separate arguments. | There has always been a lot of debate regarding what "research-level" actually means. It's changed a lot over time and it's inconsistent across various fields. (There is a plentiful supply of old discussions on tea.mathoverflow.net .) Here are my two cents... I've often heard "MathOverflow is like a colleague down the hall" and I've used that phrase to explain MathOverflow to colleagues who hadn't used it yet. It's often the case that your colleague down the hall can answer your question right away but sometimes your colleague has to think about it for a day or two. Sometimes that doesn't work and your colleague needs to ask a more specialized colleague in another department. Sometimes even that doesn't work and your seemingly innocent question might even reach the great guru... MathOverflow is a lot like that, except that there is no layering: your question is seen by your colleague down the hall at the same time as it's seen by the great guru. Does that mean that you can't ask the same questions on MathOverflow as you would ask your colleague down the hall? I like to think that whatever you would ask your colleague down the hall you could also ask on MathOverflow. That's a bit of an idealist attitude but I think it's fair. After all, MathOverflow is also about answering questions. If all questions are for the gurus then there's little interest here for mere mortals! | {
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1,516 | On Reference for invariance of essential spectrum under relatively compact perturbations , Michael Renardy voted to close with the comment "This site should not become a shortcut to substitute for literature searches", and it seems at least two others are of the same opinion. Respectfully, I'm not sure I agree, either in the context of this question or in general, and I thought I would solicit the community's input. Indeed, I thought this was the whole point of the reference-request tag, and a major part of what makes this site an asset to the community. Searching the literature for a specific result is a tedious and often unrewarding task, especially for a junior researcher or someone looking for results outside their own area of expertise who may not even know where to begin. Online search tools are not very good at this: the desired paper may state the result in different language, or prove a generalization. The situation gets much worse if one has to search for symbols. It's a time-honored tradition to shortcut this drudgery by asking an expert colleague whom you suspect might know immediately where to find your result, or at least where to start looking. But not everyone has an expert colleague down the hall, which to my mind is exactly the reason why MO was started. There's a limit, of course: we want questions which are "research level", which by consensus seems to be roughly defined as "beyond a standard first-year graduate course". I think the question at hand certainly meets that standard: I have a Ph.D. and what I like to think is a working knowledge of basic functional analysis, and I don't have any idea where to find the requested result. I don't see such questions as making a disrespectful demand on the time of others, either; a reference request can be answered in seconds by someone who knows where to find what's wanted, and everyone else can shrug and move on. Many people here invest much more time in writing detailed answers to complicated questions. I personally would gladly take the time to answer this question if I knew an appropriate reference, and would do the same for any other reference request within my limited expertise. I'd appreciate hearing any other thoughts. | Many MO questions, not just reference requests, could be answered by a literature search.
Yet, a main point of having this site is to avoid having somebody spend a lot of time searching for something that somebody else just might know from the top of their head. However, it should also be note that the emphasis here is on "a lot." Before asking a question on this site, any question not just reference requests, one better should make some effort oneself to find the answer by oneself, and this is also in the FAQs, more specifically in How to write a good MathOverflow question? (under "Do you homework") Thus, this site should be used to avoid long literarture searches, yet not to avoid all literature searches. It is difficult for me to tell, this not being my field, how hard it is to find the answer to that particular request linked in OP. For me, as a non-expert, the request seems well-written, especially I like that it mentions the related result for Hilbert spaces. And, I would thus assume, or at least give the benefit of the doubt, that OP made some effort beforehand and thus find this particular question a rather good example for a reference request question. | {
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1,820 | The term "MO-Hard" has entered the mathematical vocabulary, describing interesting questions that were asked on MathOverflow but haven't been answered in spite of efforts by many community members. Each one of these is a MathOverflow success story! Open problems are precious commodities that have driven mathematical research for centuries. While these are not necessarily at the same level as the Riemann Hypothesis and the Jacobian Conjecture, we should celebrate them and promote them! While the unanswered tab is a good way to find such gems, questions that have interesting partial answers do not appear there. In the same spirit as Best of MathOverflow , let's collect MO-Hard questions here. Questions that still appear in the unanswered list are welcome since they might disappear any day. Comments, anecdotes and other remarks are also encouraged. | Here is a prime example of a MO-Hard question that doesn't appear on the unanswered list. Polynomial bijection from $\mathbb Q\times\mathbb Q$ to $\mathbb Q$? The title says it all. In fact, the body of the question is just one line. It has had 16 answer attempts though most have been deleted after an error was found... | {
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1,862 | I have a question I am curious about: call it $Q$. There exists a posted question $P$ on MO which asks my question $Q$. More precisely, $P$ states a series of (slightly vague) questions, one of which is very clearly $Q$. The poser of $P$ has accepted an answer to $P$. However, neither this answer nor the other answers/comments to $P$ point towards an answer to $Q$. Should I post my question $Q$ (being more explicit than $P$ in what I want for an answer, in hopes that this will stimulate some response), thus taking the risk that it will be unceremoniously squashed as a "duplicate" (and it certainly would be a duplicate)? Should I edit $P$ to indicate that some part of it really hasn't been answered (though it seems rude to edit someone else's question this way, and it would still have an accepted answer)? Should I do something else? Should I just give up? | I recommend posting your version $Q$ of the question, linking to $P$, and stating explicitly why the accepted answer is not what you want. I don't like the scenario of editing question $P$ because I expect that people are less likely to answer a question that already has an accepted answer (and it feels like it undermines the original asker of $P$). | {
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1,894 | Is it the case that MO is actually split into several communities which only communicate with each other through meta-activity but have no actual mathematical interests in common? This is not sheer curiosity since personally I skip lots of questions and it would be convenient to restrict myself to fewer topics, although I have no heart to filter any tags out as it might happen that this way I never see something which might be still interesting for me; however if I would know that I am actually firmly placed inside a clearly cut out connected component, I would be more confident to filter the rest out; on the other hand if there indeed are some symptoms of disconnectedness, this might be interesting generally, indicating some lack of communication in the MO slice of the mathematical community, and maybe something should be done about it. So could one e. g. use the data explorer to somehow measure connectivity of MO? | There is some recent research related to clustering and the role of centrality on MathOverflow. Leydi Viviana Montoya, Athen Ma, Raul J. Mondragón, Social achievement and centrality in MathOverflow , Complex Networks IV, Studies in Computational Intelligence Volume 476, 2013, 27-38. DOI:10.1007/978-3-642-36844-8_3 ( PDF ) Abstract. This paper presents an academic web community, MathOverflow, as a network. Social network analysis is used to examine the interactions among users over a period of two and a half years. We describe relevant aspects associated with its behaviour as a result of the dynamics arisen from users participation and contribution, such as the existence of clusters, rich–club and collaborative properties within the network. We examine, in particular, the relationship between the social achievements obtained by users and node centrality derived from interactions through posting questions, answers and comments. Our study shows that the two aspects have a strong direct correlation; and active participation in the forum seems to be the most effective way to gain social recognition. Page 10 has a description of the clustering that can be observed on MathOverflow. Most of the clusters are quite small given that 61% of the clusters has just 2 users, see fig. 3(a). The map representing the 105 clusters in the network displayed its 6 biggest groups (denominated as G1, G2, . . . , G6) and the small box in the bottom right corner contains 99 clusters with a total of 297 nodes. Also, the 6 clusters have 97.5% of the total users in the MathOverflow network. The subgraphs (clusters) diameter, average geodesic distance and density were calculated for the 6 clusters, in order to characterise them. Cluster G2 has the same diameter than the whole network (7 edges). Clusters G6 and G3 have a diameter of 11. The six clusters show a density lower than 0.006 which is bigger than the density of the whole network (0.0014), although they are significantly low given that the density provides the ratio of direct ties in the network to the total of possible direct ties [28]. The 6 biggest clusters have a small proportion of users with the highest degree values and the highest upvotes counts, with a relevant proportion of users with low degree value and upvotes as followers. The users with a degree higher than 500 or upvotes higher than 750 or with the highest reputations are located only on the 6 biggest clusters (see fig. 3(b)). In contrast, users who have achieved a reputation of 1 (which is given when users input their personal details on the community web page) are located in the biggest clusters as followers of the main users and in the small clusters, Fig. 3(c). This is a comment that's a bit too long. It looks like the author did try to correlate clusters with tags: Specific subgroups in the network were identified based on the tags (topics) the users marked their questions with. When analysing the 3 subgroups with highest number of users (AG–Algebraic Geometry, SQ–Soft Question and NT–Number Theory) they appear to have similar network characteristics as the whole network. These subgroups contain 20%, 19% and 18% of the total users in the network respectively. The subgroups AG and NT have a diameter larger than the original network, which means the farthest two nodes in AG and NT are more distant; whereas the SQ subgroup has the same diameter as the original network (see Tab. 2). It may seem unusual that the authors identified soft-question as a subgroup but note that their methods are purely algorithmic and not based on any predefined mathematical taxonomy. On the other hand, it is not surprising that the SQ graph is similar to the whole graph while AG and NT graphs are somewhat different. | {
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2,055 | I've posted an incomplete answer to the question Does a left basis imply a right basis, without AC? which has a 50 point bounty that expires soon. My answer is basically an idea that I think (but I'm not sure) I can complete to an acceptable answer, but I'm pretty sure I'm not going to be able to do that before the bounty expires. My answer already has a few upvotes, and if I understand how bounties work, that means that I might automatically be awarded half the bounty when the grace period expires. I'd feel a bit bad if that happened, especially if I subsequently realized that my idea didn't work. Is there any way I can dodge the bounty? If I temporarily deleted my answer just before the grace period expired, would that work? | The bounty will not be awarded to a deleted answer and it will not be awarded retroactively. Thus, to temporarily delete the answer until the bounty ends indeed would be an option to avoid getting the bounty. I do however not quite understand the rationale. For the person that started the bounty the points are gone no matter what; if the bounty goes to no one the points are just lost. Thus, you do not "help" the OP in any way. If it is just you feeling uneasy about your undeserved increase in "wealth," perhaps rather then throwing the "money" in the trash, donate it to "charity;" that is take the points and start a bounty on some deserving question yourself, it could be even that same question. (Technical footnote: if you should get just half the bounty it does not suffice to start a bounty on its own.) | {
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2,167 | Recently I noticed that the software inserts the id
of the currently logged in user in the “share” link
of any MathOverflow question or answer.
When one is logged out, the “share” link comes out normal,
without any private information.
For example, the same link appears as https://mathoverflow.net/a/198099/402 or https://mathoverflow.net/a/198099 when I'm logged in/out, and 402 is my id on MathOverflow. I think it's safe to assume that users have a reasonable expectation of privacy with
respect to links to publicly available pages,
in particular, one does not expect one's own
unique user id to be inserted in the link,
allowing others to identify the user that posted the link. One doesn't have to go too far to see that this
type of surveillance activity is far from being innocent:
an anonymous referee reviewing a paper for a journal adds a link to a MathOverflow
answer in his report, e.g., in order to clarify something.
Unbeknown to him, the SE software inserts his user id in the link, revealing his identity to the author. Real-life examples of this already exist. What is the opinion of the MathOverflow community on this matter?
Do we consider such type of behavior by SE to be acceptable? Myself, I see it as an unethical invasion of privacy,
especially because the users are not informed of this type of surveillance. | I consider the current situation as problematic, and would like to see this problem adressed, e.g., by making the nature of the link more transparent and/or providing direct-link without UserID in addition with the same visibility. This is a poll answer. Please do not downvote. Up-vote competing answers instead. | {
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2,543 | Just curious ... A brand new member posted a question this afternoon, and I posted an answer. I know him quite well, and he was here in Bristol to give a seminar two days ago, and without giving it much thought I began my answer with "Hi!". The "Hi!" has disappeared. Is this something the system does automatically? Or did some evil, but very on-the-ball, moderator surreptitiously remove it? I'm not in the slightest offended or bothered, just curious ... | I began this answer with a salutation, and hopefully it was never posted, because that's what the system is supposed to do, as per Jeff Atwood's answer on Meta Stack Exchange: We now automatically remove salutations from posts as they are entered. I got really tired of performing this edit over and over, so anything matching the form of … ^ # begins at start of body
\s* # possible spaces
(
hii?(?![a-z])| # any of these greeting words
hello|
h(e|a)y(?![a-z])|
dear|
greetings|
hai|
guys|
howdy|
h(i|e)ya|
hola
)
.*? # followed by anything, up to...
(
[.,;!-]+ # one or more bits of punctuation
\s* # possible spaces
|
(\r?\n)+ # one or more newlines
) … is removed automagically at the time of submission to the server. (The regex above is not currently accurate. After the discovery of automatic hair removal the regex has been altered, though I don't know the details. If at some time the new regex becomes public — and I remember to — I'll update that part of this answer.) | {
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2,574 | In view of recent events, we've been reconsidering having some policy against anonymous users. We've always encouraged users to use real names though we have been tolerant of pseudonymous and anonymous users. As an internal moderation policy, we've always had less tolerance toward anonymous users but we never set any official rules or guidelines. That said, it is becoming increasingly clear that our lack of policy on anonymous users is becoming problematic and encourages uncivil or disruptive behavior in our community. What anonymity policy should MO have? Should we ban any users that use anonymizing tools to hide their identity? Should we require using real names? Should we maintain the status quo? Are there other things MO could do to encourage civil and responsible behavior for all users? As announced previously , the moderation team has decided to require certain users to use real names. This is meant as a means for protecting the community as well as people who may be victims of identity hacking. We aim to be fully accountable for this process and provide the community with any information or data that neither compromises the identity of users nor infringes on our privacy policy . [ Edit : We have stopped requiring certain users to use real names.] | There are two important reasons to allow anonymous users. There are countries/regions where western education, or women's education in particular is a dangerous issue. There are many more that monitor and censor their citizens' activity online. There are families that may be opposed to their children doing math. If you believe that MO has an educational mission, these users should be accommodated. This includes both pseudonymous and anonymous accounts and allowing connections via Tor. For early career mathematicians, MO can be pretty intimidating. We're all afraid of being wrong in public. Here's a fun fact: many women are more afraid to ask questions at conferences because if the question is bad, everyone will remember who asked it because you're the woman. Same story for minorities. This is a semi-professional setting, and that's terrifying. I was too afraid to post for years, and if I had to use my full name I still wouldn't. | {
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2,781 | There are quite a few very poor questions (all being put on hold quite soon after they've been asked), such as this . These questions stick around unless they get deleted by the OP (which they almost never do). Wouldn't it be nice to implement a mechanism that automatically removes questions that are on hold and have received a sufficient number of down-votes (say, 4 of them)? | This already exists, downvoted and closed questions will usually be removed automatically. The exact criteria are listed in this post on Meta Stack Exchange : Just to formally document the exact policies we have in place to
remove old abandoned / dead questions, the Community user will
delete questions in the following circumstances: If the question is more than 30 days old, and ... has −1 or lower score has no answers is not locked ...or... it was closed and migrated to a different site ... it will be automatically deleted. Internally, these are termed
"dead" questions ( RemoveDeadQuestions , or RemoveMigrationStubs in
the case of a migration). If the question is more than 365 days old, and ... has a score of 0, or a score of 1 in case of deleted owner has no answers is not locked has view count <= the age of the question in days times 1.5 has 1 or 0 comments ... it will be automatically deleted. These are "abandoned" questions
( RemoveAbandonedQuestions ). These checks are run every week across all sites. If the question was closed more than 9 days ago, and ... not closed as a duplicate has a score of 0 or less is not locked has no answers with a score > 0 has no accepted answer has no pending reopen votes has not been edited in the past 9 days ... it will be automatically deleted. These are "abandoned closed",
and show as RemoveAbandonedClosed : This check is run every day across all sites. See also: The official "How does deleting work? What can cause a post
to be deleted, and what does that actually mean?" FAQ meta post. | {
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2,902 | There has been a lot of discussion about questions that do not get answered on MSE, but are not considered 'research level' on MO and thus get closed. The problem seems to be that certain questions are too easy for MO, but get lost on MSE between the hundreds of easy-to-answer questions. (Even if you stick to a single tag (algebraic geometry in my case), many questions are easy exercises.) One could argue that the target audience of MO is primarily faculty, and that MSE seems to be used mostly by undergraduates (this is certainly the impression one gets by looking at the active questions on the main page). If this analysis is correct, could it be useful to create a new 'in between' SE page aimed mostly at graduate students and postdocs? The advantage of such a website would be that it would constitute a single place where graduate students can post and answer questions; where no question is too hard; but where one can still filter out elementary questions so that the interesting ones stick to the front page. This might also encourage more of the senior MO members to engage with the not-quite-research-level questions. Graduate school is a weird time, and the types of questions one asks and is capable of answering are a big step away from both undergraduate work and research-level mathematics. Remark. The reason I post this question is that I think there is a real problem with intermediate level questions, experienced by many people. This is one suggestion for dealing with it, but really I want to stimulate discussion rather than propose a single solution. | I believe it is impossible in general to distinguish questions asked by a graduate student and those asked by a mathematician in a domain in which they are not specialist. Since the latter are allowed on MathOverflow, it would make little sense to disallow the former or relegate them elsewhither. It is hard to argue that MathOverflow receives too many questions, or that there it is at a serious risk of being overflooded by questions by graduate students. There are also a number of questions being asked (and to avoid pointing the finger, I plead guilty myself ), and often well-received, which are obviously motivated not by actual mathematical research, but just "general intellectual curiosity" (as in "I need to know this": I hope we can all agree that this is healthy). Again, it would make little sense to allow those and not questions asked by graduate students. I think the main criteria should be something like: (1) the question's answer is not easy to find in standard textbooks on the subject, and (2) it has mathematical interest (either on its own or in order to solve a problem that does). This should exclude most cases of homework. I believe graduate students should be encouraged to take the time to think on their own before asking a question, and be sure to frame it carefully (and make sure it's not homework), but so long as they do so, and show their efforts, they should feel perfectly welcome to post on MathOverflow, and this should be made clear. In a practical sense, apart from posters who will blatantly disregard guidelines and rules because they don't even read them, and a few cranks, I suspect there's more of a tendency to err on the side of self-censorship than in the other direction. I've mentioned MathOverflow to a number of colleagues, and surprisingly many of them are apparently too shy to join, even to discuss their domain of research, because they feel intimidated by the level of the existing discussions, or for fear of seeming foolish (he who never hesitated to raise his hand and ask a question at a seminar, let him be the first to throw a stone ☺). So I would find most welcome a change that could make the site seem just a little less "elitist". | {
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3,088 | I was recently surfing around the Physicsoverflow and I have to admit I was impressed by their Review section. I could not help myself from thinking how -and if- such a feature could also be implemented here at Mathoverflow. I can clearly understand that maybe this is not that simple: Refereeing a paper in Physics can be significantly different than refereeing a paper in mathematics. Detailed checks of computations and statements seem -well at least ideally- more important in refereeing of mathematical papers while the overall estimation of the novelty of an idea or model and its relation to experimental data or phenomenological approaches seem to be the focus in lots of cases of physics papers. However, I feel that the community might have the power to add such a feature in this site, at least for some specific categories, where there are enough experts willing to undertake the job (for example algebraic geometry or number theory). I am thinking that initially, it would not necessarily have to do with refereeing of full papers (I guess that few mathematicians would like to initially submit their full paper in the site; lots would prefer a mainstream journal). However it might have to do with refereeing specific proofs of new results or parts of the whole argument. P.S.: Although one might say that initially this could just be a check-my-proof feature, what I am having in mind is something more substantial, with the ambition to evolve in more conceptual community-reviewing of both problems and arguments and finally whole papers. | I am intrigued by this idea and I think it would be a wonderful thing if it gained the support and acceptance of the MathOverflow community. So I am supportive of further discussion of the proposal. My opinion is that our current refereeing process in mathematics is basically broken, and that the professional mathematics research community should pursue alternative experimental efforts, to find out how we should best reform it. I would view such a paper-review project on MathOverflow as such an experimental effort. Perhaps it could be very successful, which would be good to know. Or perhaps it will be flawed in a way that will be good to learn. With the support of the MO community, such a system could be implemented at first on a provisional basis, with the promise to remove it after a year or two, say, if it fails. There are, of course, many practical issues to consider. At the very least, the review posts should look different than ordinary MO questions, with a different background, or they should exist in a separate stream. Does one want to impose rep limits for people to contribute papers? | {
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3,144 | Occasionally, there has been a suggestion to start a meta question to collect information that might be of interest to the MO community. This is an attempt to start such a thread. Is there any news that you think would be of wide interest to the MO community? Please exercise your discretion in any answers, and your judgement on the appropriateness or significance of any event. | Igor Shafarevich died on February 19, 2017 in Moscow at the age of 93. | {
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3,168 | I've been on this site for several years and I appreciate the site a lot but I don't like to post here anymore because no matter what I write I get some kind of sarcastic comment, or put-down, or someone edits my post (removing and adding tags, etc.). I realize that you all need to monitor the site, and that I ask stupid questions sometimes (usually I am thinking of something more and I just want a reliable resource for my little question) or ask weird questions. But, I don't see what is the harm in keeping these questions up and just not saying anything unless you have something helpful to say. I posted a question about Liouville's Theorem and I just wanted to make sure that I was thinking about it in the right way. But I got people editing my post (adding and removing tags) and a wikipedia link (why is that helpful?), so I removed the question. I think that this environment is not encouraging new ideas because I can't ask the questions I want to ask and I can't say things in the way that I want to say them for fear of all this negative feedback. I'm frustrated because I would just like a little help, not to be made fun of for asking. Any ideas? The sarcasm and patronizing tone of some of the comments really bothers me. | While it is an ongoing concern to keep the site on-topic and to maintain
its standards, it is crucial for the community how people feel when they are
asking or answering questions here -- if people enjoy using MathOverflow,
the site will flourish, and what happens otherwise is obvious. Given this, I think it can only be welcomed when people say how they feel
about using MathOverflow -- even more when the enquiry comes not just
from a pseudonymous new user_xyz , but is made by a long-term user of the
site under their real name -- and this does not depend on the merits of
the particular question the enquiry is about. Furthermore, what you write may well shed a light on the reasons for the
unfortunate but obvious strong bias towards male mathematicians among the
regular users of MathOverflow. Since you are using the site basically already since its beginnings,
and as you are a former PhD student of Joel David Hamkins ,
I assume you know the community well. In particular I don't think that
there is any need to explain to you how things are on this site.
Rather I think you could provide a valuable service to the community
if you further elaborate (say, in a discussion post on Meta) on what you
would change in order to make using the site a more pleasant experience
for yourself -- and in the same time presumably for many other people
as well! | {
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3,293 | I asked a question with multiple sub-questions, all in the same theme. There are four answers, which together answer the whole question without significant overlap. I'd like to move this question from "unanswered" to "answered," but no single answer does the job; what should I do? I could accept the answer that I like the best, but that seems unfair to the others. | One thing I've seen done in this situation -- and it may be the best option under the circumstances -- is to summarize all the answers in one master answer yourself. I would write it anew (without copying-and-pasting), tie it together nicely with a narrative thread, credit individuals as appropriate, and (important) make it community wiki. Then accept it as the answer after a couple of days. If others have more information to add, then it can go into the master answer. | {
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3,710 | Suppose I delete an answer or a question I have posted, it is still visible for users with high reputation to see that. I guess deleting an answer would mean I realise that the content is wrong or not sufficient. It is little embarrassing to know that my stupid answer/question is still visible to so many users. What is the point of this facility to high reputation users? Is it a good idea to make it visible just for me and no one else? | First of all, all of us make mistakes and you need not be more than mildly embarrassed by past errors. The user with the most reputation points on the site, Joel David Hamkins, has also deleted on occasion. So you're in very good company here; all we can do is try our best to minimize our mistakes and just keep learning -- all of us here are lifelong learners. I think the ability of high rep users to see deleted content fits within the model of a stackexchange site as being based on community moderation, with more reputable users having a greater share in moderation abilities. A gross preponderance of deleted posts may indicate a problem which should be visible to such users in order for them to effectively contribute to community moderation. For example, deleting and then re-asking questions may indicate an attempt to circumvent moderation. Or, quickly deleting a question just after getting an answer may indicate a different type of shenanigans. Self-vandalism can also be a problem. All of these and more are possibilities whose sources need to be visible in order to be accurately judged. Site moderators and community management cannot effectively do their jobs without a large "army" of vigilant observers to report what they see, so I would not recommend any changes to the set-up here. | {
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3,795 | Here I only ask questions and do not (can not answer for lack of knowledge) answer any of the questions. Sometimes I feel it is bad. Some questions that I know answer to are either closed as not research level or already has very good answers. What does MO community think about this? Is it a good practice to just take help from this site and do nothing in return? I used to do something at MSE but am not doing here. | It's fine in my opinion just to ask and not answer questions, and conversely I think it's fine just to answer and and not ask questions. In time you will probably acquire enough knowledge to feel comfortable and confident answering questions as well, but there's no particular hurry. Either way, if your questions or answers are well received, you are seen as adding value to the site. We need all kinds here. | {
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3,866 | Mathoverflow has seven moderators , but many of them seem to be inactive (at least from the point of view of an unprivileged user): for instance, they are not active on meta , and they moderated few questions recently (SEDE query thanks to Martin Sleziak; shows time-dependent results so it may change in future). It seems to me that Todd Trimble carried the burden of moderation single-handedly in these summer months, for instance. Stack Exchange claims that "we periodically hold democratic moderator elections" , but that seems blatantly false. We had only one moderator election , five years ago. Should we have new elections? I don't intend to run myself, but I have in mind one or two users that would make good moderators in my opinion. | This is what I wrote (with slight edits) at the MO chatroom : I guess I should mention that I am often in contact with my fellow moderators, especially when a sticky situation arises that I'm not sure how to handle, I'll want to consult them or get consensus. That kind of behind-the-scenes activity is of course invisible to general users. I think part of the "problem" is that I am on MO so much, and I process flags so readily (because I like having a clean inbox), to the point where other moderators often don't have much of ordinary moderation to do when they tune in. They can't be blamed for that. I could voluntarily scale back my activity, if that would be considered a healthy thing to do... I would also like to mention that other moderators are involved with labor-intensive activities such as setting up MathOverflow, Inc. as a non-profit (that's a lot of paperwork and legal work), financial activities, and improvement of the citation function, to name a few. This may help offset any impression that other moderators aren't doing much. Finally, let me mention that we moderators have a yearly meeting where one of the agenda items is to discuss whether we should have another moderator. Of course my input is sought since I am currently the most active moderator for day-to-day on-site actions. So far I have reported not feeling a personal need for more, but it's of course fine to discuss this at meta. | {
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3,894 | I just made a question in MO to discuss the correctness of the proof provided by Prof. Atiyah for the Riemann hypothesis (link here: Is there an error in the pre print published by Atiyah with his proof of the Riemann hypothesis? ). I understand that's usually outside the scope of MO, but this time is the work of an Fields medalist claiming to solve one of the most important math problems currently. Is there a way to reword my question so it could be discussed here? In case the answer is negative, could someone provide a forum with similar quality where such proof could be discussed? Thanks and sorry for the problems caused. Héctor | After some internal discussion, the moderators have agreed to post the following text. There are calls from the community to enunciate a firm and consistent policy for what questions are permissible or not regarding Atiyah's attempted proof of RH. If for a moment we blind ourselves to the name on the paper, the natural and appropriate reaction would be to dismiss it out of hand, without fuss and without worry that we were missing out on anything. In the name of consistency, I think that would be the right reaction here as well, and that should really be the policy. So any question that asks for responses on whether this is right or wrong, or if there is something there, should be treated in the way it's always been treated: we at MO do not vet papers that purport to solve famous open problems. And in the case of 5-page articles that announce a solution of RH: we don't discuss them at all. The question will be closed. My personal opinion is that the situation and the appropriate reaction is made only slightly more complicated by knowing it was Atiyah. There are indeed allusions to sophisticated concepts such as the Todd genus (there is a "Todd function" which is somehow related to the Todd genus). Careful and precise questions about such concepts, at a professional level, are always in principle allowable, and they may mention that some such concept was spotted in Atiyah's article, but these should not turn into cover for discussing the current topic. We don't think it's possible to spell out policy in advance that will cover every such circumstance; some matters have to be treated on a case-by-case basis, with input from the community. (What's the expression? "Hard cases make bad law"?) Please: just be prudent, and avoid drama. We have no doubt there will be those who cry "censorship!", "suppression of free thought!", etc. Or, less dramatically: how do you know there's nothing there? Well, none of us know for a fact, and obviously Atiyah's track record from when he was in his prime will give some people pause: for many years he has led mathematicians across difficult country. There may well be a tragic aspect to what is unfolding before us. Let's please preserve some dignity for the man. Don't worry: if there is truly mathematical takeaway, it will be picked up by the experts. RH will never be solved in a day: any serious solution will take months or years to be pored over and analysed by thousands at home, in offices, in seminar rooms around the world. MathOverflow, especially where it is vulnerable to regrettable social media contaminants, can not play all the necessary roles here. We do not have to be the public bulwark against the conspiracy theorists. Let's keep doing what we do best: provide a clearinghouse to deal with well-circumscribed, sober mathematical questions that can be authoritatively addressed in less than three pages. Any general public statements we want to make for now can go on this Meta page. If the mathematics begins to look serious, then well-delineated parts can be discussed at Main. | {
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3,976 | As part of implementing the new unified themes across the network, we're gradually rolling out updated site themes for each site. As of today, we have enabled your updated site theme for testing. If you can't see it right now, that's by design! This is a very early test implementation of your design and we need your help finding issues with it before we make it live for everyone permanently. So, keep in mind, there will be things that need fixing! We'll address those things as we can. If you'd like to review it, here's how: How do I enable it? Click here and check the "Beta test new themes" option. This will turn on the new theme for all sites that have one in testing, including this one. Here's more info on how to opt in. You can uncheck the box to revert to the older theme until the site is live for everyone. Note, while turning it on is immediate, it will take a few minutes to revert to the old view - but it will go through! What type of feedback do we need? On this post: Bugs related to this site's design elements Please help us look for issues/bugs related to the theme design and how we have mapped the old theme to the new. This needs to be done within the limits of the new unified theme . This could include colors of sections of the design or text, problems with JavaScript add-ons (if applicable), the logo or top banner appearance or other artwork. You can also feel free to ask questions about the new layout if you're unsure how to navigate it. On Meta Stack Exchange: General concerns about left nav or theming There are some things that are definitely changing everywhere and can't really be adjusted on a per-site basis. A few of them include: Top banner is shorter in height, so some artwork has to be adjusted along with some logos. Left Navigation is active everywhere (but can be collapsed into a menu by visiting your site preferences - instructions here ). Responsive layout is active, which lets the site adjust as browser widths change - no side scrolling (some pages haven't been updated, yet, though). For now, if you prefer the scrolling, you can disable this by clicking the "disable responsiveness" link in the footer. Many site elements including tags and voting arrows are standardized across the network. Link underlining is active. In an effort to make links more visible, they are now being underlined. If you have concerns or issues regarding the left nav or the overall approach we are taking to theming, then this Meta Stack Exchange post is the right place for feedback. As I mentioned earlier, there are some unique design elements like voting arrows and tags that are being standardized in this process. Keeping these custom elements makes our ability to maintain the sites too complex and, while we're very sad to see them go, we're in a difficult position of needing to make the site designs work together so that we can continue to address feature requests and bugs that will make your Q&A experience better. This is addressed in a Meta Stack Exchange post if you want more detail. What new themes? If you're like, "What the heck are you talking about?", then you should read the Meta Stack Exchange post entitled Rollout of new network site themes (and maybe the posts it links to for the full background). To follow along with the rollout of these new themes, go here . Thanks so much for your constructive feedback! Oh, Who am I? If you don't know me, I'm one of the Community Managers here at Stack Exchange. I'm here to listen to your input and convey it to our Design team for responses and fixes to bugs. I'll do my best to respond to your concerns and explain whether changes we've made are bugs that can be changed or if they're by design and why. | The presence of three distinct colours for "unanswered, answered, accepted" was a helpful feature IMO. In the new layout the "unanswered" questions no longer stand out. I regret that change. | {
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3,981 | The comments on the OP for the following question are disconcerting: Why is Voevodsky's motivic homotopy theory 'the right' approach? From what I can gather, the OP must have had something like a confederate jack, swastika, or some other such thing. Two different users comment on it, including a comment that some images are unacceptable to use even once. They follow up by saying they will never answer questions asked by the OP. Such a response is so strong that, to the uninitiated, it could seem ironic. That is, what makes things confusing is that the original image has already been changed. Should the comments be deleted? Can they be clarified? What is the situation? | For people who are either unfamiliar with US history (either due to growing up in other countries or who had White Supremacist textbooks in school), here are the first two paragraphs of the state of Mississippi's explanation of why they seceded and joined the country which flew this flag: In the momentous step which our State has taken of dissolving its connection with the government of which we so long formed a part, it is but just that we should declare the prominent reasons which have induced our course. Our position is thoroughly identified with the institution of slavery-- the greatest material interest of the world. Its labor supplies the product which constitutes by far the largest and most important portions of commerce of the earth. These products are peculiar to the climate verging on the tropical regions, and by an imperious law of nature, none but the black race can bear exposure to the tropical sun. These products have become necessities of the world, and a blow at slavery is a blow at commerce and civilization. That blow has been long aimed at the institution, and was at the point of reaching its consummation. There was no choice left us but submission to the mandates of abolition, or a dissolution of the Union, whose principles had been subverted to work out our ruin. That we do not overstate the dangers to our institution, a reference to a few facts will sufficiently prove. Here's Georgia's first two sentences: The people of Georgia having dissolved their political connection with the Government of the United States of America, present to their confederates and the world the causes which have led to the separation. For the last ten years we have had numerous and serious causes of complaint against our non-slave-holding confederate States with reference to the subject of African slavery. This flag represents, as it always has, treason in the name of White Supremacy and the defense of slavery and all that was part of the slavery system (the death of millions, children separated from their parents, systemic rape, etc.). It is one of the most purely evil symbols in the history of humanity. Most recently it returned to prominence during the civil rights era when states added it to their flag to show their support of Jim Crow and lynchings and their opposition to equal voting rights and civil rights. Anyone who flies it or defends it is an enemy of that which is good in society and I will have nothing to do with them, whether they’re a mathematician or not. | {
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4,351 | I believe that fedja has disproved a conjecture of Erdős et al. when commenting on my question Almost monochromatic point sets , but I'm unable to contact fedja regarding this. What shall I do? Shall I just casually drop a footnote in my upcoming paper that an unknown user has solved an Erdős problem? | This would not be a first, see arXiv:1909.00177 The citation (which I think follows the best practice) is [6] Fedja, Communication on the MathOverflow website (2018), available
online at https://mathoverflow.net/questions/125861 | {
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4,368 | [Long-time 10k+ MO user here, asking this question anonymously for reasons that should be obvious. Added Oct 16: My access to this account will self-destruct in 3, 2, 1 .... (sorry, won't be able to accept an official answer. For what it's worth, I strongly support Tim Campion's suggestion.)] This question is not meant to be a place to discuss the pros and cons of the dumpster fire on meta.SE, or the underlying issues that started it. Go there if you want to get depressed. Also, I think that only moderators are in a position to answer this question. The short background is that StackExchange Inc. 1) is trying to implement a new Code of Conduct (CoC), and it's proving difficult, and 2) has retroactively relicensed all existing content, questioned by many as being of dubious legality. These are separate issues, but have both contributed to a wide feeling (expressed through community voting and extensive commenting) that SE Inc. is making a mess of things, one way or another. Since MathOverflow uses the SE platform, but is actually a different organisation it is not clear what exposure (in the sense of risk) MO has to the recent controversies. Are our moderators bound by the same agreement as the SE network moderators? Will the CoC apply here, when it is finally sorted out? Were contributions to MO retroactively relicensed (making this question outdated)? Again, the intent of this question is not the content of the CoC or the relicensing issue, but to get in writing the facts of where MO stands in relation to these from a contractual/legal/etc way. Edit (To clarify some things) I asked this question in a slightly vague way, partly because I didn't want to pre-empt any position or bring up debates here. But I've read a bit more, and Johannes pointed out some relevant facts in an answer. So here are some more focussed questions. Again, this is not to debate the merit or otherwise of the below points , I'm looking for official answers from mods or MO owners/board members on policy about changes that StackExchange Inc makes. StackExchange relicensed all contributions users had made to their websites (from CC-By-SA 3.0 to CC-By-SA 4.0, which change the CC people say can't be made without permission), but this has also relicensed all MathOverflow content too. Is this compatible with the agreement between the MathOverflow corporation and StackExchange Inc ? I presume that there is very little objection to the principles of the new Code of Conduct (CoC), and find it nigh-impossible to forsee any circumstances in which MathOverflow as an organisation would object to the now in-position wording, and adopting the CoC as official here (were it a choice). However, the official FAQ on the CoC, which has given rise to concerns among many StackExchange users, is getting rather distant from any document that I can see referred to under the legal agreement between MathOverflow and StackExchange Inc. The CoC is linked to from MathOverflow pages, and so is, it seems, in effect and binding. I haven't seen, after some cursory clicking about, explicit links from MathOverflow to the contentious FAQ. Does this latter nonetheless carry force on MathOverflow to the extent it does on the StackExchange network? Will all future policy changes in the same manner also immediately and automatically apply on MathOverflow? (Added: I note that this type of question was raised nearly six years ago , to which it seems the official answer was, to paraphrase, MathOverflow has an informal understanding with StackExchange Inc that SE Inc employees shouldn't interfere with our moderation as we can choose to leave the network. However, this seems to me to be a bit like the nuclear deterrent ...) Perhaps all of this is moot. But I hope MathOverflow is not hit with the same ugly stick terrible optics that StackExchange Inc has encountered in trying to create an environment that once was expressed through 'be nice'. Update: Yesterday a new FAQ regarding the pronoun discussion has been released. This new FAQ is based on previous input from the community and it seems that the acceptance of these new rules is (so far) much higher. | I think that given the sort of turmoil experienced of late at Stack Exchange, it might be wise for us here at MO to take certain measures to reinforce our status as an entity independent from Stack Exchange. I'm no legal expert, but I think our migration agreement is rather vague on many points concerning exactly what our status is. And if we establish too much precedent of deferring to Stack Exchange, that could come back to bite us down the road. For example, we might contemplate Writing our own Code of Conduct. It could even be verbatim the same as Stack Exchange's, but it would be ours to interpret as we see fit. Agreeing on our own licensing convention. That might mean we use the same license as Stack Exchange uses, but it would be our decision. Negotiating some written agreement with Stack Exchange over when they can and cannot unilaterally "fire" one of our moderators. I don't know what kind of standing we have to do any of these things, but I think steps like this might be worth discussing. | {
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4,386 | In case you missed the news, upvotes on questions now grant +10 reputation instead of +5 , and the change has been implemented retroactively (most if not all users have already had their reputation recalculated). This change was welcomed mostly neutrally or positively (who doesn't like free rep?) but I did hear some concerns from other users about where this may take us (mostly those who I know personally, but this meta question is very likely motivated by a similar concern (edit: that question is now deleted; it asked about the impact of the change on the number of questions posted)). I am aware that while MathOverflow is part of Stack Exchange, there is a unique agreement between MO and SE (as described and linked here ). I admit I have not read the entirety of the agreement so I don't know exactly what it allows in regards to MO following different rules than other SE sites. My questions are then this: Would it be possible, if the community and/or the moderation team on MO decide so, to revert this reputation change on this site? If there is such a possibility, should we take it? Opinion ahead: I am personally not a fan of the change. While I understand where the SE are coming from introducing it, arguing that asking a good question is an art in itself, I feel like it is not as true on this website as it is elsewhere. While there are of course some great questions there (like this one ), I do still believe that writing a good question is generally not as much of a demanding task as coming up with a good answer, the latter often requiring more insight and sheer work, and they should be rewarded accordingly. There are of course people who disagree with me on this stand (this was the most upvoted feature request ), but I know people who agree, and I would like to put this to a discussion. | Let me answer from the perspective of someone who is not a mathematician but follows this community for certain topics of interest. This is a community of professional mathematicians where, indeed, questions are usually very well researched and posed, and there's virtually no risk of rewarding homework dump. So, if there's a community in which questions' upvotes really deserve the same value of answers' upvotes is this one. | {
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4,704 | When I started graduate school ten (!) years ago, a more senior Ph.D student at the time told me about MathOverflow and encouraged me to participate. Ever since then I have found it immensely useful. Some responses (see Richard Stanley's answer: Some restricted weighted sums , and the paper that this answer appeared in ) have directly helped me with my thesis work. Many answers I received here have been very helpful for my subsequent research. However, I feel like MO today is quite a different place than what it was ten years ago (this perception possibly influenced by nostalgia), and in particular, possibly less friendly to newcomers. In the early days one could get away with asking questions that are borderline research level and it's less likely that the question has already been asked. My question is: would you still encourage graduate students to participate in MO, and if so, at what stage of their PhD would you recommend that they start participating? | I guess I still would. The clear case is when one can answer a question. The regular practice of picking up a question that is accessible, answering it, and communicating the answer can be very beneficial. Even I am learning from it a lot and I'm by no means new to "random problem solving". So, if a student (or anybody in general) can answer questions on MO, I would definitely encourage them to participate. Just warn them that it may become addictive, so they should balance it with their regular duties. I have also never seen any "unwelcoming behavior" with respect to people who post answers, at least, as long as purely mathematical discussions are concerned. The issue arises when somebody's contribution is reduced to asking endless questions of the type "I cannot figure out this place in the textbook, can you help me?". There are questions of this type that are still eligible for MO, but many of them are on the borderline and would be better redirected to MSE or just to the student adviser. So, I would suggest that in such cases the students view MO as the last resort, not as a help hotline. Any questions about student research (i.e., something that is not readily found in the textbooks or, if you prefer, something that falls under the "missing-lemma" tag) have always been welcome and I try to answer them and to protect them from closing as much as I can even if they look a bit "homeworkish". I would encourage such questions any time. Some of them are now being asked on MSE, which is a pity, because they usually just get flushed by the stream there unless somebody attaches a bounty. As to "MO being less friendly to newcomers", my feelings are mixed. On the one hand, we introduced a lot of friendly perks like the automated reminder to (try to) be nice whenever responding to someone who posts for the first time. On the other hand, there still seems to be a strong movement to eradicate everything that is not "research-looking" when judging from pure appearance (though I would say it was much stronger a year or two ago). I mean such things as, for instance, voting to close for "the lack of motivation". My own stance is that any clearly posed mathematical problem that I cannot solve in under 10 minutes should pass and the OP has no obligation to explain in detail where it came from and what it is related to. It especially applies if the OP is a student: quite a few of them have enough trouble with merely understanding and stating what exactly they need. The MO may be not exactly what it was 10 years ago (all is changing, all is flowing, and some part of the discrepancy in perception may come from the fact that we ourselves are not exactly what we were 10 years ago), but it still looks like a nice and interesting place to be at to me. As soon as the student is ready for a mathematical discussion, he or she is welcome to enter. That may happen at any "stage of PhD" and at any age. I wouldn't be surprised to learn if some participants of MSE who ask there questions that might be suitable for MO as well are, in fact, high school teenagers or undergraduates. If in doubt, just try MSE first, but if you see that your questions merely earn you reputation there but are left unanswered, switch to MO. Those are just my two cents, but I'm an old-timer. It would be really interesting to hear what the newcomers have to say, especially the young ones. | {
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