# turning the car off when you pump gas **URL:** \ **Category:** Factual Questions\ **Created:** [March 12, 2012, 1:04am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505 "2012-03-12T01:04:41Z")\ **Posts on this page:** 16\ **Page:** 3
**Author:** ![anson2995](https://avatars.discourse-cdn.com/v4/letter/a/c77e96/32.png) [@anson2995](https://boards.straightdope.com/u/anson2995)\ **Post date:** [March 12, 2012, 7:05pm UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/41 "2012-03-12T19:05:21Z")
> [@engineer\_comp\_geek](#): > > There are two examples in the PEI report (I just checked - you can get to it from Rick’s link upthread) where they note that the vehicle had been left running. It’s not clear from the circumstances though if the running engine actually had anything to do with the static discharge. In both cases the driver got in and out of the car as well, which may have generated the static charge. Not disputing the issue of static charge, just the idea that the engine itself createsan explosion risk. FWIW, I linked to an earlier version of the PEI report in the 2005 thread I referenced, so I’m with you on this one. ---
**Author:** ![Morgenstern](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@Morgenstern](https://boards.straightdope.com/u/Morgenstern)\ **Post date:** [March 12, 2012, 7:22pm UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/42 "2012-03-12T19:22:22Z")
There are a few things those of you who fuel your car with the engine running may have overlooked. In some jurisdictions, it’s illegal to fuel a running vehicle. That probably explains why the stations pay for those “Turn vehicle off when fueling” sighs posted. Also, modern vehicles, with sophisticated emission systems, frequently run system tests while the vehicle is running. It has no way of knowing if your’re stopped at a traffic light or for fuel. It’s just a matter of time before such a test happens while you’re fueling your car with the engine running. You’ll first notice a problem when you see the “Check Engine” light illuminated on your instrument cluster. This is because the fuel system is a sealed unit. The vapors are captured and later burned. Opening the fuel tank with the engine running will trigger an error code IF a system test runs at that time. After a trip to the mechanic, and a wallet a hundred dollars lighter, you’ll understand the the advantage of turning off your vehicle when fueling. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [March 12, 2012, 7:23pm UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/43 "2012-03-12T19:23:03Z")
> [@anson2995](#): > > Not disputing the issue of static charge, just the idea that the engine itself createsan explosion risk. [Failure Analysis: Cell Phone Usage at Gas Stations](http://www.exponent.com/files/Uploads/Documents/CellPhoneReport.pdf) > [@Failure Analysis](#): > > **Motor Vehicles as Ignition Sources** > The engine in a motor vehicle can act as an ignition source if operated in a combustible environment. Some potential ignition sources are: alternator brushes, starter motor assembly, electric fans on the radiator, grounded spark plug wires, and even hot surfaces on an exhaust system of an abnormally performing engine. Most of these sources would be closer to the ground than a cell phone in operation, and thus closer to any combustible mixtures of gasoline vapor and air resulting from filling operations or a spill. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [March 12, 2012, 7:54pm UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/44 "2012-03-12T19:54:23Z")
> [@engineer\_comp\_geek](#): > > Keeping the engine running keeps charge building up, mostly due to the moving belts. Otherwise, any charge built up would dissipate through the vehicle’s tires. So there is a slightly higher risk with leaving the engine running. Wouldn’t that require the pulleys to be fixed to bits of car that were electrically separate? And where’s the charge supposed to come from that dissipates through the tires? ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [March 12, 2012, 8:11pm UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/45 "2012-03-12T20:11:38Z")
> [@naita](#): > > Wouldn’t that require the pulleys to be fixed to bits of car that were electrically separate? It may not exactly be an ideal Van de Graaff generator but the moving belts can still generate a charge. I found this video which you may find interesting: [![](https://img.youtube.com/vi/6d7pfA_bo6s/hqdefault.jpg "Hyundai 2.7L delta powered Van de Graaff generator") ](https://www.youtube.com/watch?v=6d7pfA_bo6s) > [@naita](#): > > And where’s the charge supposed to come from that dissipates through the tires? Engine belts and pulleys aside, cars will also generate a charge just from moving down the road. It’s pretty much the same process as by which clouds become electrically charged. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [March 12, 2012, 8:19pm UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/46 "2012-03-12T20:19:17Z")
> [@beowulff](#): > > ETA: newer cars will set the Check Engine Light if they detect the gas cap is loose while running, so that’s another reason not to do this. Having refilled a couple of times without shutting down the engine over the years, and several times at full service stations leaving the engine running I can attest that this short time of taking the fuel cap off does not set off the check engine light. ---
**Author:** ![Tastes\_of\_Chocolate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tastes_of_chocolate/32/3232_2.png) [@Tastes\_of\_Chocolate](https://boards.straightdope.com/u/Tastes_of_Chocolate)\ **Post date:** [March 12, 2012, 8:44pm UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/47 "2012-03-12T20:44:23Z")
> [@kanicbird](#): > > Having refilled a couple of times without shutting down the engine over the years, and several times at full service stations leaving the engine running I can attest that this short time of taking the fuel cap off does not set off the check engine light. Having accidentally not tightened the gas cap all the way, and having the check engine light come on very shortly after restarting the engine, I can attest that you are taking your chances. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [March 12, 2012, 8:55pm UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/48 "2012-03-12T20:55:06Z")
> [@Tastes\_of\_Chocolate](#): > > Having accidentally not tightened the gas cap all the way, and having the check engine light come on very shortly after restarting the engine, I can attest that you are taking your chances. Once the offending condition (unsealed fuel tank) is fixed, these kinds of fault codes reset themselves after a few key/start cycles; it’s not typically necessary to interface with the ECU and force a reset. ---
**Author:** ![anson2995](https://avatars.discourse-cdn.com/v4/letter/a/c77e96/32.png) [@anson2995](https://boards.straightdope.com/u/anson2995)\ **Post date:** [March 12, 2012, 9:02pm UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/49 "2012-03-12T21:02:15Z")
> [@Machine\_Elf](#): > > [Failure Analysis: Cell Phone Usage at Gas Stations](http://www.exponent.com/files/Uploads/Documents/CellPhoneReport.pdf) > > [Quote=Failure Analysis] > > The engine in a motor vehicle can act as an ignition source if operated in a combustible environment. Some potential ignition sources are: alternator brushes, starter motor assembly, electric fans on the radiator, grounded spark plug wires, and even hot surfaces on an exhaust system of an abnormally performing engine. Most of these sources would be closer to the ground than a cell phone in operation, and thus closer to any combustible mixtures of gasoline vapor and air resulting from filling operations or a spill. [/QUOTE] And if any of those things are an ignition source while you’re pumping gas, they’re also an ignition source as you’re pulling in or as you’re exiting. As with the idea of cars slipping into gear, this is an example of an already dangerous car continuing to be dangerous. The real question here is whether a new risk is created by leaving an otherwise un-dangerous car running while you are filling up. And while the static issue is real (and well documented), it is not directly related to leaving the engine running. Its important to understand what are real dangers and what aren’t. For example, its virtually impossible for a cell phone to accidentally trigger an explosion, but it’s very possible for a cell phone to distract you and cause an overflow… which could be dangerous. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [March 12, 2012, 9:05pm UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/50 "2012-03-12T21:05:42Z")
> [@engineer\_comp\_geek](#): > > It may not exactly be an ideal Van de Graaff generator but the moving belts can still generate a charge. I found this video which you may find interesting: > [http://www.youtube.com/watch?v=6d7pfA\_bo6s](http://www.youtube.com/watch?v=6d7pfA_bo6s) > > Engine belts and pulleys aside, cars will also generate a charge just from moving down the road. It’s pretty much the same process as by which clouds become electrically charged. That makes sense. I wouldn’t have thought the pulleys were sufficiently isolated from the rest of the engine for that to occur and your mention of both pulleys and belts, and charge dissipating through the tires in the same set of arguments had me confused. ---
**Author:** ![Fubaya](https://avatars.discourse-cdn.com/v4/letter/f/c2a13f/32.png) [@Fubaya](https://boards.straightdope.com/u/Fubaya)\ **Post date:** [March 13, 2012, 1:11am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/51 "2012-03-13T01:11:32Z")
> [@Tastes\_of\_Chocolate](#): > > Having accidentally not tightened the gas cap all the way, and having the check engine light come on very shortly after restarting the engine, I can attest that you are taking your chances. The check is done when the vehicle is started, not at a random point while running. On some (all?) cars, the engine light will go off if it passes X number of checks so while some people will freak out and drive to the dealer, the mechanically inclined may find or deduce the problem and know it’s nothing to worry about and that if they wait a day or two the light will go off. ---
**Author:** ![pullin](https://avatars.discourse-cdn.com/v4/letter/p/c57346/32.png) [@pullin](https://boards.straightdope.com/u/pullin)\ **Post date:** [March 13, 2012, 2:09am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/52 "2012-03-13T02:09:48Z")
> [@JoshuaSD](#): > > My two cents: > > Google “child knocks car into drive” and the results should convince anyone that this is a very bad idea. I jumped out\* of my running truck once, and left my Border Colllie inside in the air conditioning. As he ran excitedly from window to window, he managed to hit the door lock button and locked me out of the truck. I was in the middle of nowhere and my cellphone was inside with him. I had to lure him from one side to the other and get him to jump up on the door for a long time before he finally managed to randomly hit the button again, unlocking it. He had no idea what the game was about, but he enjoyed it. If I’m not shutting it off, I at least lower one of the windows now. \*I wasn’t refueling. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [March 13, 2012, 5:07am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/53 "2012-03-13T05:07:57Z")
> [@Fubaya](#): > > The check is done when the vehicle is started, not at a random point while running. On some (all?) cars, the engine light will go off if it passes X number of checks so while some people will freak out and drive to the dealer, the mechanically inclined may find or deduce the problem and know it’s nothing to worry about and that if they wait a day or two the light will go off. Umm no. It depends on the car maker and model. I can name cars that test right after the key is turned off and I can name cars that test with the engine running 17 minutes after engine start. Both of those cars are built by the same company BTW. ---
**Author:** ![NorthernBiker](https://avatars.discourse-cdn.com/v4/letter/n/50afbb/32.png) [@NorthernBiker](https://boards.straightdope.com/u/NorthernBiker)\ **Post date:** [March 13, 2012, 11:35am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/54 "2012-03-13T11:35:17Z")
When I used to live in Fairbanks during the winter no one turned their vehicle off. Jumping out and touching a cold gas pump in -50 is bad enough. Waiting in a rapidly cooling car, for your 38 gallon tank to fill up is not going to happen. I do not remember a single persons car catching fire or exploding! There is probably a small non-statistical possibility that your car could catch on fire, so gas stations don’t want to bear the risk. ---
**Author:** ![Morgenstern](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@Morgenstern](https://boards.straightdope.com/u/Morgenstern)\ **Post date:** [March 13, 2012, 1:48pm UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/55 "2012-03-13T13:48:28Z")
> [@Fubaya](#): > > The check is done when the vehicle is started, not at a random point while running. On some (all?) cars, the engine light will go off if it passes X number of checks so while some people will freak out and drive to the dealer, the mechanically inclined may find or deduce the problem and know it’s nothing to worry about and that if they wait a day or two the light will go off. This is only partly true. The self tests are run when the vehicle starts, **AND** when the vehicle is operating. Certain systems, such as closed loop operation, can only be tested while the engine is running and warm. If you’re interested in the frequency and duration of said tests, contact your manufacturer. ---
**Author:** ![FluffyBob](https://avatars.discourse-cdn.com/v4/letter/f/ecb155/32.png) [@FluffyBob](https://boards.straightdope.com/u/FluffyBob)\ **Post date:** [March 13, 2012, 2:30pm UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/56 "2012-03-13T14:30:19Z")
I think the most important issue is simplicity and elimination of possible modes of failure. Turning the car off is a simple step that that eliminates a possible source of ignition, a collision hazard, and a breathing hazard. There are probably more. Most disasters demonstrate multiple layers of missed steps, any one of which taken properly could have prevented or mitigated the disaster. [Previous page](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505.md?page=2)