I just noticed recently that my gas tank seems to be building up a lot more pressure than usual. The vapors from the tank seemed to be quite warm as well. The car is running great. I replaced the fuel pump a few thousand miles ago. I first noticed this when I took the car for its smog test last week and the tech even noticed this and thought it was a little unusual. The pump has a little hum to it, but i think it's normal...to tell you the truth I never paid much attention to any of this until after my smog check. It passed. Any suggestions? Thx

 

so you noticed it because the tech told you?
Is it possible that its had this quirk since you've had the car, or since you put the pump in?

 

I have always noticed a certain amount of pressure when taking the cap off, but in this instance it was a very high amount of pressure and a heat from the vapors that was way above normal compared to anything else I have ever felt from this car before. It was alarming. One thing I can add is that I did replace the gas cap with a new one before I took it in for the smog. Assuming the guy behind the counter gave me the correct cap, it fit great and seemed to seal a little better than my old cap and looked identical. I have since reinstalled my old gas cap but have not driven far since doing that.

 

I have the same problem as you do. Strange though, as my car makes kind of a low howl to it. I take off the cap when driving for a good amount of time, and you can hear the pressure escape. I've never known what causes this problem. Something I've done is, instead of tightening the cap till it clicks, tighten the cap enough, but not so tight (leaving it a little loose, but a snug fit to let the pressure escape). I was told that I had a bad cap as well, but I honestly don't think that's the problem.

 

My old cap fits a little loose too, but I feel better having it back on. I'll have to take it out and drive it soon and recheck. I wasn't to keen on the new smog check they have in CA where they pump your tanks now with nitrogen to check for tank leaks....stupid. Do they have this smog check in AZ? I swear my fuel pump is noisier since that damn check. Then they squeeze off the lines going to the charcoal cannister as well when they do that test, while your sitting there praying to god your 18 year old hoses are up to the task.

 

not too sure about this...but if youve ever seen the fuel sending unit in the tank, there is a fuel return. with all the new bells and whistles such as the new pump and cap, you may just hold pressure better in your tank, and when driving long distances, obviously your exhaust gets nice and hot, and guess what is RIGHT above the exhaust. You guessed it, the gas tank. Im sure the fine engineers at GM thought of this, but the only thing between your exhaust pipe and gas tank is about a 1/16" piece of sheet metal. That is probably causing a bit of heat in the tank, which would also create a little more pressure.

Hope this can help you out a least a little bit.