I dont know where to put this so I'll try here. This has happend to me twice. One time I know I was a idiot and filled it up, the nozzle clicked and I filled it more. I came home, parked in the garage and two hours later I had a puddle of gas on the floor. Lesson learned. Today, I filled the car, let it click off and stopped. I rotated the cap untill I got three clicks and off I went. Went out to the garage and I smelt gas. I looked under the car and nothing on the floor but saw where gas had leaked onto the side of the tank. I pulled it out, sprayed some cleaner up there and washed it off. No more smell.

I was wondering what this could be? I dont have a vented cap and when I took the cap off I got the whoooooosh of air pressure. I was told that was a good thing. I've removed the cap a few times and did not get that whooooosh sound and did'nt have the gas smell after adding gas. I put in 7 gallons of gas on this particular stop. I'm wondering if I have too much pressure.

 

That leak makes me wonder if you have the infamous problem with your gas tank filler neck getting a crack or pinholes. Lucky for you, if you do, there actually is a chance that you can go get your tank replaced by gm for free. look up the recall on the filler neck. I don't have links so I'm hoping someone else will chime in here to help with more specifics

 

I wondered the same thing but if I had a crack or pinhole then it would'nt hold pressure when I opened the cap. Then again is has to be open somewhere to get the leaking.

 

have you looked at the filler neck to see if there is anything noticeable? just grab one of those extendable mirrors and a flashlight and check all around where the filler meets the tank

 

And there can definitely still be pressure even with a crack. For example, if the hole is small enough, and possibly your charcoal canister is clogged or something like that. Anything is possible.