gas tank contracting and expanding?

hpi_jeep · October 8, 2005

something in the rear of my truck is expanding and compacting and it sounds like you are hitting a coffee can with a hammer, it is really bad after you get done driving it and turn it off. it will ping/thud 5-10 minutes after you have turned it off. it could possibly be a heat sheild or something but it does have me worried. im affraid the gas tank is creating vacume and its sucking the tank up and letting it loose, if it does this to many times it could create a hole im sure.

TIA

GM-Tech · October 9, 2005

Exhaust systems will do this as they cool down. There's a TSB on newer trucks for this very problem and it involves cutting off the muffler heat shield and strapping on a replacement.

My Colorado did this big time for the first few thousand miles. I could hear it snapping and popping in the house for 10 to 15 minutes after I parked in the garage. I didn't bother with cutting off the heat shield as I knew it would improve with age and it wasn't worth my effort. It has 4500 miles on it now and I don't recall it doing it at all now. Maybe a small amount, but not so much that I notice like when it was new.

hpi_jeep · October 9, 2005

it is hard to explain, it doesnt sound like something is cooling off. it actually sounds like the tank has been sucked up and then the pressure is being released and it pops.

i am not 100% sure it is the fuel tank but it is the only thing i can think of. BTW the truck has 50k miles on it, so it should be well broken in.

GM-Tech · October 9, 2005

At 50k miles, the exhaust normally wouldn't suddenly begin to do this.

Simple enough to know if it's the tank... loosen or take the gas cap off when you park it. Or, when you take the cap off do you get a rush of air being sucked in?