Like people leave their engines idling while waiting for a pump and that’s not an issue… and if there was a chance of a spark traveling back along the line and ignigting the tank (and thus, the station), then why doesn’t this happen during normal operation?
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At least in modern vehicles, I don’t think there’s much of a risk of a spark traveling through the car’s fuel system from the engine back to the tank. But a running car does produce a lot of heat and potentially sparks from various sources that could potentially ignite fuel vapors that are in the air from people operating the pumps incorrectly.
Overall it’s probably a very low risk, but it’s also pretty darn easy to shut your car off for a few minutes while you refuel, so why not turn the engine off and lower that risk even more?
I think it’s more of a theoretic risk but easy to accommodate w/no downsides. The risk is that a spark could ignite gas vapor. Vapor would be near the nozzle/fuel cap and shouldn’t be in quantities that would easily ignite except in situations where something is malfunctioning. Due to the incredibly large numbers of times people fuel their cars, though, if turning off the car has even a tiny tiny positive effect it has been deemed the safe and recommended practice for everyone.
Gasoline turns into a vapour fairly easily. If you can smell gas, there’s at least some in the air.
So the spark/flame doesn’t have to come out the gas tank. It could come out the tailpipe, the alternator or other electrical things under the hood, etc. Shut it down. Gas burns, but gas vapours are downright explosive.
Modern cars are pretty good and probably safe enough, but if someone or something catches fire at a gas station, people want to blame or sue even if it’s the customer’s fault. Being able to just point at a rule sign and say “you broke the rules” is a great trump card to have.
The major danger is not the running engine causing the pump to explode. The real danger is if your car pops into gear while you’re fueling it. There’s nobody in the car who can stop it, and the pump’s hose is liable to be torn off. Good news is the hose should have a special valve on it that should automatically seal when sheared. Still, it’s a danger to the property and a major inconvenience to be down a pump, so gas stations ask you to turn off your car to keep this non-zero possibility event from happening.
I worked at a dealership several years ago, and I was told that the bigger issue is that modern fuel systems are pressurized, so if you take the cap off to add fuel, the computers will think there’s a leak in the system and trigger a dash light. Which causes customers to freak and hassle the service department when they get a bill for a minimum 1 hour of labor just to tell them to read the manual. Or listen to what they were told when they bought it. But also, if you do accidentally do this, or just simply not tighten the cap enough, the dash light *should* clear itself after a couple on/off cycles (after you’ve tightened the cap properly). But I always do what I was told, which is when replacing the gas cap, turn it until you hear 2 or 3 clicks (you’re not hurting anything, they’re designed this way) and that should prevent triggering the light, at least for that reason. I’ve never had an issue when following this procedure. And also, even as small as the chance may be, accidents happen. It is marginally safer in case things don’t quite go according to plan.
It’s not just about fire.
A car that is turned off can’t be left accidentally in gear to idle crawl away and crash into stuff.
When you shut off and park a car you make it safer to work on.
Was allways told it wasn’t a danger of explosion, but can mess up the fuel float in the tank and confuse the computer
It isn’t. Modern fuel injection systems eliminated any risk, if there even was one to begin with.
You’re filling the tank at a gas station with your car running. You expect the auto fill to trip and shut down the pump when the tank is full. Sometimes it doesn’t trip and ends up pumping gasoline all over the ground. This fuel on the ground vaporizes and if anything is hot enough near it, or a spark, kaboom.
It’s nothing to do with a spark traveling in fuel lines or pumps or anything.
It has everything to do with the fact that a running engine is generating thousands of sparks per minute to keep itself running, and that fueling a vehicle emits a constant cloud of fuel vapors.
In ideal conditions the sparks and the fuel vapors never interact. (The spark stays in the engine, and the fuel vapors float away with the wind).
The problem arises if your ignition system had any damaged or worn out parts. A cracked ignition coil, a damaged distributor, a chafed spark plug wire, a cracked spark plug boot, or a broken spark plug could cause the spark to occur OUTSIDE the engine. And if you have a cloud of fuel vapors coming off of somebody’s filler nozzle it could ignite the vapors and cause a fire or explosion.
Most modern vehicles don’t have to worry about distributors, plug wires or old-fashioned coils allowing sparks outside the engine. But turning off the engine makes it so that there’s no spark to worry about until you close everything up and start the engine to drive away.
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