# Should I Turn Off the Engine While Pumping Gas? **URL:** \ **Category:** Factual Questions\ **Created:** [June 1, 2004, 4:13pm UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089 "2004-06-01T16:13:34Z")\ **Posts on this page:** 20\ **Page:** 4
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [August 30, 2014, 7:45pm UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/61 "2014-08-30T19:45:13Z")
> [@GusNSpot](#): > > {nitpick}I just watched that & at the very end it said he tried to use the cell phone as light source.{/nitpick} The point being that yes, a cell phone can be a problem. > > YMMV šŸ˜ƒ Furthermore this is an apples to kumquats comparison. You car: outdoors so no build up of vapors, vapor recovery nozzle on end of hose, quite likely the car itself has itā€™s own vapor recovery system (ORVR system) The video: bulk fuel carrier, inside a building allowing vapors to accumulate (whoā€™s idea was this?) open fuel port on top of the vehicle (basically an 18" diameter hatch in the top of the tank) allowing vapors to escape. These vehicles require a ground clip be attached for static electricity. Just a slight difference in conditions. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [August 30, 2014, 7:54pm UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/62 "2014-08-30T19:54:28Z")
> [@Killing\_Time](#): > > Itā€™s not the act of taking the cap off that triggers the engine code and makes the check engine light come on. It is the act of running the engine with the cap off. And Iā€™m not sure what you mean by it being ā€œjustā€ an emissions issue. You wonā€™t be able to pass a smog check with the check engine light on, and I would imagine a malfunctioning smog system is putting more pollution into the air. If this can be avoided by the simple act of turning off your engine before you pump gas, why would you not do it? This is incorrect. Not all cars check the evaporative system with the engine running and (a big AND) the detection is not continuous it will occur at on point in the drive cycle. If the conditions are not met during the test window the test is put off till the next drive cycle. A check engine light from refueling with the running does not create additional pollution in the air and is not what I would call a malfunction of the pollution control system. ---
**Author:** ![purplehorseshoe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/purplehorseshoe/32/2996_2.png) [@purplehorseshoe](https://boards.straightdope.com/u/purplehorseshoe)\ **Post date:** [August 30, 2014, 7:55pm UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/63 "2014-08-30T19:55:46Z")
If I did math on my fingers correctly, the OPā€™s widdle bitty baby is almost done with elementary school! :eek: ---
**Author:** ![rsat3acr](https://avatars.discourse-cdn.com/v4/letter/r/a3d4f5/32.png) [@rsat3acr](https://boards.straightdope.com/u/rsat3acr)\ **Post date:** [August 31, 2014, 12:26am UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/64 "2014-08-31T00:26:23Z")
> [@GusNSpot](#): > > I disagree somewhat. > Aircraft, it is usually static arc between the fueling hose & the area around the fill port. Moving liquid will induce as electrical charge difference between the nozzle and the aircraft. Many military places still use the static cable before opening the filler inlet. I have hot fueled many piston engined aircraft. Just be sure the hose & aircraft are grounded together before opening the cap/plug and then keep the line/nozzle & tank in constant contact until finished. All I know is that when we were in the field we fueled with the aircraft running with an open port and no grounding cable. Crew chief stood next to the helicopter with the aircraft fire extinguisher in hand. On base we always used a grounding cable. Did it that way both at Ft. Rucker and Ft. Bliss. ---
**Author:** ![DingoelGringo](https://avatars.discourse-cdn.com/v4/letter/d/9d8465/32.png) [@DingoelGringo](https://boards.straightdope.com/u/DingoelGringo)\ **Post date:** [August 31, 2014, 12:36am UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/65 "2014-08-31T00:36:03Z")
Actually one can put a hand on the end of the tail pipe while the car is running, it is not that hot. This is all just superstition. Something made up by politicians so they could justify their existence. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [August 31, 2014, 12:48am UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/66 "2014-08-31T00:48:49Z")
> [@DingoelGringo](#): > > Actually one can put a hand on the end of the tail pipe while the car is running, it is not that hot. This is all just superstition. Something made up by politicians so they could justify their existence. Note you said end. Read upthread for my post on actual converter temps. ---
**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:** [August 31, 2014, 1:08am UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/67 "2014-08-31T01:08:20Z")
> [@rsat3acr](#): > > All I know is that when we were in the field we fueled with the aircraft running with an open port and no grounding cable. Crew chief stood next to the helicopter with the aircraft fire extinguisher in hand. On base we always used a grounding cable. Did it that way both at Ft. Rucker and Ft. Bliss. Jet A ā‰  Gasoline. ---
**Author:** ![rsat3acr](https://avatars.discourse-cdn.com/v4/letter/r/a3d4f5/32.png) [@rsat3acr](https://boards.straightdope.com/u/rsat3acr)\ **Post date:** [August 31, 2014, 2:31am UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/68 "2014-08-31T02:31:42Z")
we used JP4, donā€™t know if that is another name for Jet A. ---
**Author:** ![usedtobe](https://avatars.discourse-cdn.com/v4/letter/u/ec9cab/32.png) [@usedtobe](https://boards.straightdope.com/u/usedtobe)\ **Post date:** [August 31, 2014, 3:00am UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/69 "2014-08-31T03:00:51Z")
I believe this is carry-over from when fuel tanks were located in the cowl - the filler was between the windshield and the (not even close to air-tight) hood. A spill on one of those cars could be guaranteed to start a fire. Related Q: Why the silly little step up from the garage to the living quarters? Cars used to leak fuel as a matter of pride. Ford had the gas shutoff (remember: tank is at the top of the cowl) by the passengerā€™s knees until 1931, when it was moved into the engine compartment. And gas fumes stay on the ground. By having the living quarters up a few inches, you ensured the vapors would not get into the living quarters and blow the place apart when it found the first pilot light or cigarette. How much fuel does your car drip? But we still have to build that step, and the door has to be rated for fire resistance. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [August 31, 2014, 3:30am UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/70 "2014-08-31T03:30:59Z")
> [@rsat3acr](#): > > All I know is that when we were in the field we fueled with the aircraft running with an open port and no grounding cable. Crew chief stood next to the helicopter with the aircraft fire extinguisher in hand. On base we always used a grounding cable. Did it that way both at Ft. Rucker and Ft. Bliss. I did at Ft Rucker also but was never at Bliss. Did all kinds of hot fueling overseas. Like I explained up thread, you can keep all the static charges out by the sequence of your actions during refueling. I knew that stuff before I got out of high school. There is the right way There is the wrong way There is the bossā€™ way There is the ARMY way ( NAVY, Air Force, Marine, Coastguard, government,etc., ) Do it the right way and the instructed way when they are lookingā€¦ or donā€™t let them see it. LOL šŸ†’ Our Captain at one place just quit looking when we would grease the swash plate & tail rotor bearings while the chopper was running. We always had them greased and never lost a bearing like some outfits did. We had a way cool CO. šŸ˜‰ ---
**Author:** ![rsa](https://avatars.discourse-cdn.com/v4/letter/r/839c29/32.png) [@rsa](https://boards.straightdope.com/u/rsa)\ **Post date:** [August 31, 2014, 3:46am UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/71 "2014-08-31T03:46:48Z")
Modern automobile fuel systems are pressurized. If you leave your car running the on-board diagnostics detects a loss of pressure and causes the check engine light to come on. So while itā€™s not a worry about those gas fumes igniting, they are escaping much more while the engine is running due to the pressurization. So while there may not be much pollution coming from the tailpipe, thatā€™s pure hydrocarbon vapor pouring out of the tank. This is also why the check engine light can come on if you havenā€™t tightened your gas cap properly. The light will go out after a bit of driving but your little addition to global warming is still out there. :smack: ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [August 31, 2014, 5:33am UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/72 "2014-08-31T05:33:35Z")
> [@rsa](#): > > Modern automobile fuel systems are pressurized. If you leave your car running the on-board diagnostics detects a loss of pressure and causes the check engine light to come on. So while itā€™s not a worry about those gas fumes igniting, they are escaping much more while the engine is running due to the pressurization. So while there may not be much pollution coming from the tailpipe, thatā€™s pure hydrocarbon vapor pouring out of the tank. This is also why the check engine light can come on if you havenā€™t tightened your gas cap properly. The light will go out after a bit of driving but your little addition to global warming is still out there. :smack: This is 99% wrong. Fuel tanks on modern cars are NOT pressurized except for some cars (Jeep Chrysler, and a few Volvos) that pressurize the tank for a minute or so to check for leaks once a drive cycle. As a matter of course while running I know of no car that keeps the tank at above ambient pressure. During the test phase, a few do, all the time? No car does this. ---
**Author:** ![sbunny8](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@sbunny8](https://boards.straightdope.com/u/sbunny8)\ **Post date:** [August 31, 2014, 5:34am UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/73 "2014-08-31T05:34:28Z")
I find it hard to believe that all of the followingā€¦ - hot catalytic converters from engines on cars which just arrived at the station - spark plugs in engines on cars which are pulling into the station - static electricity caused by people getting in and out of their cars - starter motors used to restart the engine after fueling - spark plugs in engines on cars which are leaving the station are considered to be acceptable risksā€¦ and yet somehow, when you add to that long list just one more tiny item: - spark plugs in an engine which is actively being fueled suddenly weā€™ve crossed a line and this is considered an unacceptable risk?? I call shenanigans. If itā€™s dangerous to have a hot catalytic converter, shutting off the ending for a few minutes wonā€™t make any difference. The CC is still hot. If itā€™s dangerous to have spark plugs firing, shutting off the engine while fueling wonā€™t change the fact that people are pulling into the station and leaving the station and all those spark plugs are firing. And shutting off the engine will require you to activate the starter solenoid when you get ready to depart. The only justification I can see for shutting off the engine is for the comfort of the other people around you who donā€™t want to breathe your fumes or listen to the sound of your idling engine. But I suspect the real reason is that somebody had a bright idea to make it a law and the legislators voted for it because it sounded like a good idea even though thereā€™s very little real logic behind it. ---
**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:** [August 31, 2014, 5:51am UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/74 "2014-08-31T05:51:57Z")
> [@sbunny8](#): > > and yet somehow, when you add to that long list just one more tiny item: > > - spark plugs in an engine which is actively being fueled > suddenly weā€™ve crossed a line and this is considered an unacceptable risk?? I would think that you have much more of a danger coming from the moving rubber belts on the engine rather than the spark plugs. The belts act as kind of a Van de Graaff generator, creating a static charge that builds up on the car. Then when you touch the car you create a ground path for the static discharge, and since your hand is close to the fuel nozzle this static discharge also happens to be in the same area where the gas fumes are. Cars build up a static charge all the time while they are running, partly from the belts and partly from the air moving over the carā€™s surface. When you stop, the charge dissipates through the tires, though modern rubber formulations are more insulating than older tire formulations used to be. If you keep the engine running you keep replenishing that charge instead of allowing it to dissipate. Static discharge causes on average about half a dozen pump fires per year (more in some years, less in others). Leaving the engine running increases this already known risk. Now granted, half a dozen fires per year isnā€™t much compared to the many millions of cars that fill up repeatedly during that same year, so the chances of a fire are admittedly small. But they do happen. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [August 31, 2014, 6:03am UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/75 "2014-08-31T06:03:51Z")
In my 40+ years of working on cars I have seen exactly one car where the fan belt acted as a Van de Graaff generator. It was caused by a bit of fuzz from a prior fan belt rubbing the crank pulley. I took a video as I figured Iā€™d never see it again. ---
**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:** [August 31, 2014, 2:05pm UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/76 "2014-08-31T14:05:50Z")
> [@sbunny8](#): > > The only justification I can see for shutting off the engine is for the comfort of the other people around you who donā€™t want to breathe your fumes or listen to the sound of your idling engine. But I suspect the real reason is that somebody had a bright idea to make it a law and the legislators voted for it because it sounded like a good idea even though thereā€™s very little real logic behind it. You are neglecting one thing - motion-caused accidents. Turning off the car reduces the likelihood that the car will be accidentally knocked into gear by a child or a dog. Granted that this is less likely these days due to the interlock switch on the gearshift, but itā€™s still a possibility. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [August 31, 2014, 2:41pm UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/77 "2014-08-31T14:41:20Z")
The definitive, 100% correct answer can be reached with simple logic. If keeping the engine running were likely to cause fires or explosions, then the same gasoline vapour that would hypothetically be ignited would be ignited by other running cars pulling into the fueling station. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [August 31, 2014, 2:44pm UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/78 "2014-08-31T14:44:18Z")
> [@GusNSpot](#): > > Our Captain at one place just quit looking when we would grease the swash plate & tail rotor bearings while the chopper was running. > > We always had them greased and never lost a bearing like some outfits did. We had a way cool CO. šŸ˜‰ That soundsā€¦difficult to do if the rotors are spinning. Were the rotors actually turning when you did this? ---
**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:** [August 31, 2014, 2:47pm UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/79 "2014-08-31T14:47:35Z")
> [@Habeed](#): > > The definitive, 100% correct answer can be reached with simple logic. > > If keeping the engine running were likely to cause fires or explosions, then the same gasoline vapour that would hypothetically be ignited would be ignited by other running cars pulling into the fueling station. No. You are neglecting distance and time. ---
**Author:** ![Son\_of\_a\_Rich](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/son_of_a_rich/32/5439_2.png) [@Son\_of\_a\_Rich](https://boards.straightdope.com/u/Son_of_a_Rich)\ **Post date:** [August 31, 2014, 2:49pm UTC](https://boards.straightdope.com/t/should-i-turn-off-the-engine-while-pumping-gas/248089/80 "2014-08-31T14:49:59Z")
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