building pressure in gas tank

[41husk]

My Charger 500 is making periodic loud sounds from the gas tank.  When I pop the gas cap it releases a huge amount of pressure.  This does not happen if I don't secure the gas cap?  What is going on?

[70 sublime]

One very sunny day I parked my 68 in the drive way with just over 1/2 tank of gas in it
My drive way has a slope so the back end was higher

Walking past the car I could smell gas and see some seeping out around the cap and I thought what the heck is going on

I pushed the button and the cap popped open and gas shot a foot up in the air full size of the fill tube

What I figured my problem was there was just the right amount of gas in the tank to cover end of fill tube and when the air got hot it expanded to make pressure and out it came
Only did it once but think maybe the little vent tube on the side of the fill pipe was plugged up ( with a mud wasp ? ) and not letting the tank breath 
If the vent was working it still would have filled the car frame with the gas that should have vented out

[JR]

Your vent hose that runs up the filler neck is likely clogged. Sounds like it can't pull in air to replace the fuel that is being consumed from the tank, and creating a vacuum.

Does your car have California emissions? If not, then the only vent line for the tank is that tiny vent hose.  Try blowing it out with an air hose or a metal coat hanger.

[alfaitalia]

You are talking vacuum...he's saying pressure!

[JR]

I figured a vacuum situation was more likely, but even if it is positive pressure, I still bet the vent tube on the filler neck is clogged.


If it wasn't, any positive pressure would escape through it.

[csx4590]

I had an issue where the shop I used routed the vent tube back into the system so the car would suck the line dry and cause the gas tank to collapse inward. Then when you popped the cap, the pressure would release. Check the vent line to see if A) it is routed to where the pressure can escape (like the frame rail) or B) that the vent line is not clogged as others suggested...

[PlainfieldCharger]

Mine was also clogged causing the gas tank to collapse a little and release vacuum when the gas cap was opened. It was the vent tube that goes to the frame rail. The vent hose/line was original and the nipple that comes out of the fuel tube is slightly restricted from the factory. Just had a bunch of junk in it from being in storage. Paper clip did the job.

[303 Mopar]

If your using a fuel cap make sure its vented.

[Nacho-RT74]

I have being on same deal since ever. It get worst with heat.

Cap is vented ( Stant ), vent line on top of gas tank is fine

Need to note, the vent line allows to enter the air while gas tank is getting emptied, but not to release the gases pressure.

No vapors canister system on any charger built down here