If this is in the wrong place, please move it.

I went to fill up my gas tank this morning, and as I opened the gas cap, could hear air pressure escaping. There seemed to be a lot of it, too. I couldn't feel if it was coming out or going in, but I have to assume the pressure in the tank was negative, since the last time the tank was open it was full of fuel. It has done this before, any time I go too long before I fill the tank (less than ¼ tank). is this normal, or should I do something about it?

BTW, the fuel system is factory for an '85 carburated car.

 

It's not a big deal if it was going out, which it most likely was (as mine typically does). If there was a whoosh sound of air going into the tank, that wouldn't be too good.

There is a pressure relief valve that allows excessive pressure to vent. As long as it isn't defeated or plugged, you shouldn't have a problem. Sometimes the evap canister doesn't vent the tank enough, either, but I've never heard of it really being a problem.

 

good deal, thanks!