What for? Why you should turn your engine off at the gas station

No doubt you’ve seen all the rules in gasoline stations while you're filling up.

These include:

• Turn your cellphone off while in the station
• No smoking on the premises at all times
• Motorcycle riders are not allowed to sit on their bikes while refueling.

But there’s another rule that many people wonder about: turn your engine off while refueling.

Why does this rule exist? How does it keep everyone in a gas station safe?

Stopping thieves

If we look back at the reasons people turned their cars off when refueling, one is that gas caps weren’t as secure as they are now.

Back then, they were simply caps that were hinged on one side, making it fairly easy to siphon out fuel if you were, say, a gas thief. The solution was the locking gas cap.

And it should come as no surprise that many drivers opted to put the key that opened it on the same keychain as their car keys – making it impossible to open the gas cap without removing the key from the ignition barrel.

Eventually, the locking fuel filler cap and fuel door were introduced and the need for locking caps eventually faded.

Stopping infernos

Another more pressing reason is tied to the concept of fuel combustion itself.

Gasoline is extremely volatile and will ignite even at room temperature, so long as it is provided with a spark.

Back before fuel injection, cars fitted with carburetors would experience something called flooding, where excess fuel would wind up in the carburetor’s fuel bowls and leak out into the combustion chambers.

The gasoline would then vaporize because of the engine's temperature and get vented into the atmosphere, which is a major hazard.

Imagine the scenario at a gasoline station – you pull up, decide you don’t need to turn your engine off in your vintage Volkswagen Beetle because you’re only topping up a few liters. It’s a hot day and you’re the last in line for this batch of cars.

You open your fuel tank and the rush of fuel vapors comes out. It just so happens that you have a slightly overflowing fuel bowl and a broken high-tension wire – fuel, spark, it’s not hard to guess what happens next.

Diesels aren’t as prone to this problem as gasoline cars, however. Since diesel requires high compression to ignite, it won’t ignite even when it’s lit with a match, so having a diesel engine on while refueling isn’t as big of a risk as it would be.

That said, once the practice becomes a habit, it could carry over if you replace your oil burner with a gasoline car.

Modern failsafe

Thankfully, modern vehicles prevent such things from happening now.

In most cases, the fuel filler door is electronically operated and the circuit that operates it sometimes does not activate if the engine is on.

But while it is convenient, it’s always best to form the habit of turning your engine off before refueling. You can never be too sure.

It was a three-second job when keys were still involved, so how bad can it be now that push-to-start buttons are becoming more and more common, right?