Does the gas tank have a metal cap covering the hole?

[Gregory Gawaran]

Originally Posted by strat61caster

It's probably located further down the "neck" of the fuel tank. If I remember correctly it HAS to be there by law to prevent fumes from escaping the tank, they figured out in the 80's that the fumes that were being emitted while filling up and letting a gas tank "breath" were incredibly damaging to the environment so they came up with systems to trap them.

Now when you fuel up that big rubber donut creates a seal which channels the fumes in your empty tank to the tank under the gas station as your tank gets filled up, same thing happens when the gas station gets their tanks refilled and then the fumes get transported back to the refinery. Not sure what happens to them if they're re-processed into something or just disposed of in a less damaging way to the environment than venting to the air.

This I didn't know, I knew its purpose but didn't know it was a regulation.

[strat61caster]

Originally Posted by Gregory Gawaran

This I didn't know, I knew its purpose but didn't know it was a regulation.

My post kind of strayed into the refueling component but the basis of the regulation is to prevent fumes from escaping the tank and polluting the atmosphere. There is probably some form of pressure relief in an emergency so the tank doesn't balloon up but for the most part tanks are sealed.

[root]

Yeah, modern fuel systems are sealed but the gas cap has a safety release that goes at a certain pressure. I know that because my other car would vent there eventually.
I know a some of cars now don't even have a screw on gas cap anymore.

[jdcorbitt3]

It is no longer required, since we will get a check engine light if we leave the gas cap off. That was also designed so you couldn't put a larger diameter leaded gas nozzle just into the filler neck and gravity feed the tank. It required you to push the narrower unleaded nozzle in the neck in order for fuel to flow. I don't think there is leaded auto gas anymore, so the flapper valve is no longer necessary.

John