# 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:** 20\ **Page:** 1
**Author:** ![copperwindow](https://avatars.discourse-cdn.com/v4/letter/c/4af34b/32.png) [@copperwindow](https://boards.straightdope.com/u/copperwindow)\ **Post date:** [March 12, 2012, 1:04am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/1 "2012-03-12T01:04:41Z")
do you really need to turn the car off when you pump gas? what can happen if you don’t, and what are the chances? ---
**Author:** ![Lacunae\_Matata](https://avatars.discourse-cdn.com/v4/letter/l/8491ac/32.png) [@Lacunae\_Matata](https://boards.straightdope.com/u/Lacunae_Matata)\ **Post date:** [March 12, 2012, 1:16am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/2 "2012-03-12T01:16:29Z")
I’m curious about this one. My husband always leaves it running, and it makes me vaguely nervous! ---
**Author:** ![SmartAlecCat](https://avatars.discourse-cdn.com/v4/letter/s/67e7ee/32.png) [@SmartAlecCat](https://boards.straightdope.com/u/SmartAlecCat)\ **Post date:** [March 12, 2012, 1:16am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/3 "2012-03-12T01:16:46Z")
Also: how many things have actually happened to any cars that didn’t turn off? How is it turning your car off on one side of the gas pump different from the car starting and driving away on the other side of the gas pump? ---
**Author:** ![eldowan](https://avatars.discourse-cdn.com/v4/letter/e/848f3c/32.png) [@eldowan](https://boards.straightdope.com/u/eldowan)\ **Post date:** [March 12, 2012, 1:49am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/4 "2012-03-12T01:49:23Z")
My WAG: On a car with a faulty electrical system, there is a slight possibility of a bad ground (or something) that causes a spark when the nozzle is inserted into the tank, causing an explosion. Not likely, and shot from the hip, but have you seen some of the cars people drive? ---
**Author:** ![automagic](https://avatars.discourse-cdn.com/v4/letter/a/a698b9/32.png) [@automagic](https://boards.straightdope.com/u/automagic)\ **Post date:** [March 12, 2012, 2:03am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/5 "2012-03-12T02:03:22Z")
My best guess is that it has to do with fuel vapors. Until fairly recently most cars with fuel injection systems had return lines. This means that any fuel that was sent to the engine by the fuel pump, but not used by the engine, was sent back to the fuel tank. The returning fuel was at a considerably higher temperature than the fuel in the the tank. The higher temperature is normally not a problem since the fuel tank is sealed but it you open it, like when you pump gas, the vapors can escape. The fuel vapors can harm the atmosphere and also increase the chance of fire. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [March 12, 2012, 2:05am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/6 "2012-03-12T02:05:06Z")
Click and Clack have discussed this at length. Their conclusion: it reduces the possibility (no matter how remote) of accidents, both fire, and collision (putting the car into gear while reaching for your wallet, etc.) 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. ---
**Author:** ![Zsofia](https://avatars.discourse-cdn.com/v4/letter/z/7bcc69/32.png) [@Zsofia](https://boards.straightdope.com/u/Zsofia)\ **Post date:** [March 12, 2012, 2:24am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/7 "2012-03-12T02:24:05Z")
A month ago I had to sit and wait at a pump while a truck moved back a tad so I could get the hose to reach, so I ended up accidentally leaving the car on (which I only realized after I fueled up!) I scooted out of there in terror that somebody noticed - I’m so glad to realize that the risk of me blowing everybody up was relatively small. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [March 12, 2012, 2:26am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/8 "2012-03-12T02:26:20Z")
> [@eldowan](#): > > My WAG: > > On a car with a faulty electrical system, there is a slight possibility of a bad ground (or something) that causes a spark when the nozzle is inserted into the tank, causing an explosion. Impossible. ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [March 12, 2012, 2:30am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/9 "2012-03-12T02:30:24Z")
Cars have been known to jump out of park and run into their owners. I cite one example, but this has come up with cars consistently since I grew up in the 70’s. I never step out of my car without turning it off. Certainly, I turn it off before filling up. I really hate seeing any kids standing near cars idling in park. Its just foolish and an unnecessary risk. > [@](#): > > On June 10, 1980, NHTSA made an initial determination of defect in Ford vehicles with C-3, C-4, C-6, FMX, and JATCO automatic transmissions. The alleged problem with the transmissions is that a safety defect permits them to slip accidentally from park to reverse. As of the date of determination, NHTSA had received 23,000 complaints about Ford transmissions, including reports of 6,000 accidents, 1,710 injuries, and 98 fatalities–primarily the young and old, unable to save themselves–directly attributable to transmission slippage. > **[Ford Transmissions Failure to Hold in Park](https://www.autosafety.org/ford-transmissions-failure-hold-park/)** > > % ---
**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, 2:32am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/10 "2012-03-12T02:32:17Z")
Cars generate an electrical charge while running, due mostly to the rubber belt(s) moving around the front of the engine (they also generate static charge just due to moving down the road). If you leave the car running it makes it more likely for you to have a static discharge when you reach for the pump when you are done fueling, which can lead to a pump fire if the mixture of fuel and air is just right. On average there are roughly a half a dozen or so pump fires due to static electricity every year. Not all of those are due to leaving the engine running. Many for example are caused by people (more often women) getting back into the car to keep warm and generating a static charge when they slide across the seat to get back out. Considering how many people fuel up every day the chances of something bad happening are admittedly pretty small. But, they aren’t zero. Turning off the engine greatly reduces those chances, and if you do go back inside the car to keep warm, when you get back out, touch something metal on the car some distance away from the fuel pump and your gas tank to get rid of any charge that may have built up. If you are interested in the details, the petroleum equipment institute (PEI) keeps statistics about these incidents, which used to be available on their web page. I haven’t checked lately but they are probably still there. You don’t get a great deal of detail about every event, but sometimes they note things like whether or not the vehicle was left running. ---
**Author:** ![eldowan](https://avatars.discourse-cdn.com/v4/letter/e/848f3c/32.png) [@eldowan](https://boards.straightdope.com/u/eldowan)\ **Post date:** [March 12, 2012, 2:49am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/11 "2012-03-12T02:49:19Z")
> [@beowulff](#): > > Impossible. Good to know, ignorance fought. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [March 12, 2012, 2:50am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/12 "2012-03-12T02:50:23Z")
> [@beowulff](#): > > Impossible. [Would you like to bet on that](http://www.pei.org/PublicationsResources/SafetyResources/StopStaticCampaign.aspx)? Not caused by a loose ground, but static discharge none the less. Also fires can occur if you fill a gas can while in the bed of a pickup that has a bed liner. ---
**Author:** ![Ms\_Boods](https://avatars.discourse-cdn.com/v4/letter/m/5e9695/32.png) [@Ms\_Boods](https://boards.straightdope.com/u/Ms_Boods)\ **Post date:** [March 12, 2012, 2:55am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/13 "2012-03-12T02:55:54Z")
According to Jay Leno, if you drive a 1955 Buick Roadmaster, if you leave the car on, you might get ahead of the pump. [![]( " - YouTube") ](https://www.youtube.com/watch?v=dlXJrcSBIH0) ---
**Author:** ![Digital\_is\_the\_new\_Analog](https://avatars.discourse-cdn.com/v4/letter/d/a88e4f/32.png) [@Digital\_is\_the\_new\_Analog](https://boards.straightdope.com/u/Digital_is_the_new_Analog)\ **Post date:** [March 12, 2012, 3:45am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/14 "2012-03-12T03:45:14Z")
I had a friend who insisted that if it were really dangerous, there would be an interlock that forces us to turn the car off. _sigh_ I don’t know the technical answer…but I feel certain if I turn the car off, I won’t be in danger. If I leave the car on, I may or may not be in danger. Given those two choices, it’s easy… -D/a ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [March 12, 2012, 4:09am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/15 "2012-03-12T04:09:13Z")
> [@Rick](#): > > [Would you like to bet on that](http://www.pei.org/PublicationsResources/SafetyResources/StopStaticCampaign.aspx)? > Not caused by a loose ground, but static discharge none the less. > Also fires can occur if you fill a gas can while in the bed of a pickup that has a bed liner. He said “electrical problem with the car” - static discharge can occur whether the car is running or not. ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [March 12, 2012, 4:14am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/16 "2012-03-12T04:14:49Z")
> [@Ms\_Boods](#): > > According to Jay Leno, if you drive a 1955 Buick Roadmaster, if you leave the car on, you might get ahead of the pump. > > [http://www.youtube.com/watch?v=dlXJrcSBIH0](http://www.youtube.com/watch?v=dlXJrcSBIH0) Peter Arno had a cartoon like that 'way back when in _The New Yorker_, which I can’t find online. A gas station attendant is filling up an enormous, idling convertible and says to the driver, “Would you mind turning it off, sir? It’s gaining on me.” ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [March 12, 2012, 5:14am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/17 "2012-03-12T05:14:55Z")
I’ve only seen someone do it once (I was in the car) and it made me very nervous, but I’m glad to know other people do it too. ---
**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\ **Post date:** [March 12, 2012, 6:42am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/18 "2012-03-12T06:42:05Z")
My car (Peugeot 207) has a locking cap that opens with the car key. So you have to turn the car off to release the key and then go out and unlock the cap. Once the cap is opened, the key gets stuck there so you can’t use it until you put the cap back in place and lock it again. However, there is a small button on the side of the cap that if depressed releases the key. I once did that and restarted the car while it was refueling. One little problem though. Althought the car was filled to the brim, the needle got stuck somewhere in the middle. I did a long ride after that, but the needle didn’t get where it was supposed to be. Eventually the problem fixed itself the next time I refuelled the car. ---
**Author:** ![pullin](https://avatars.discourse-cdn.com/v4/letter/p/c57346/32.png) [@pullin](https://boards.straightdope.com/u/pullin)\ **Post date:** [March 12, 2012, 10:32am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/19 "2012-03-12T10:32:31Z")
> [@Rick](#): > > [Would you like to bet on that](http://www.pei.org/PublicationsResources/SafetyResources/StopStaticCampaign.aspx)? > Not caused by a loose ground, but static discharge none the less. > Also fires can occur if you fill a gas can while in the bed of a pickup that has a bed liner. Is it the bedliner that isolates the gas can? I’ve never really understood this one. I figured that the metal-to-metal contact when you insert the nozzle in your car’s fuel tank zeroes out any building charge, and that what is missing when filling a fuel tank in an ungrounded car. I once got a lecture about this from a well-meaning individual while filling a bunch of gas cans in my pickup bed (I didn’t want to lift them all back in). I silenced him by pointing out that I had grounded the bed itself with a large piece of angle-iron running to the asphalt. I have no idea whether that would work, or whether I need to ground to the pump, like they do with airplanes. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [March 12, 2012, 11:35am UTC](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505/20 "2012-03-12T11:35:37Z")
The problem occurs when you have a plastic gas can. Static builds up from the fuel flowing into the can. If the can is on the ground the charge disapates. However if you leave the can in the bed that has a bed liner the can is insulated. When you remove the nozzle A spark can jump and ignite the vapors. I saw this happen at Willow Springs Raceway once. Guy filled up a 5 gallon race jug sitting in the bed of his truck. The fire was IMPRESSIVE. They red flagged the race and rolled all the fire equipment to deal with it. Bottom line is put the can on the ground when you fill it. [Next page](https://boards.straightdope.com/t/turning-the-car-off-when-you-pump-gas/615505.md?page=2)