Pressue Still Building Up In Gas Tank

[daveh]

Hey guys,

This is a follow-up to a previous question about the pressure building up in my 1971 Challenger gas tank, even if it sits for a week or two without driving it.  I replaced the cap with a vented one and that didn't work.  I open the cap and whoosh a lot a pressure.  Some of you have said that it's normal but I've never had a car that's done this unless the tank was low on gas and never just from just sitting.  BTW everything is new, gas tank sending unit, vented cap, etc.

My possible solution:  What if I install a new sending unit the one with the return line.  And on the return line I install a fuel filter along with a stretch of hose facing down so no water or muck will get in there?  This should allow air in to stop the pressure from building.  I think this will resolve the issue what are your thoughts?  Thanks

Dave

[Mike70]

Seems that I read in a post that someone just drilled a 1/8 inch hole in the gas cap and this fixed the problem. Would be a lot easier than changing the sending unit!

Mike

[Purple73Cuda]

I had the same problem with my road runner. It turned out that the vent tube that runs into the frame was plugged. Try blowing your vent lines out with compressed air.

[MEK-Dangerfield]

If your gas cap is vented, there is no way pressure would be building up inside. By the way, I drilled a small hole in my gas cap. With the flip-top gas cap I have, there is no way anyone will know.

[daveh]

It's a locking vented cap that goes under the flip top also where exactly do I drill it?

[Katfish]

I'd be careful about drilling a hole in the gas cap, this will let gas, as well as the vapors escape. 
Might cause some paint issues long term.

Better way would be to get a 70 style filler tube which has a nipple for venting purposes.

http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Board=QuestionAnswer&Number=5258046&Searchpage=1&Main=5258046&Words=drill+%2Bgas+%2Bcap+2RTSE&topic=&Search=true#Post5258046

[Purple73Cuda]

IMHO, by drilling a hole in the gas cap, you are putting a bandaid on the car instead of finding and repairing the cause of the pressure buildup. The car should not be building up pressure in the tank. This leads me to believe that you have a plugged tank vent.
I agree with KATFISH about drilling a hole in the cap, this  could cause gas and vapors to escape and possibly damage the paint.

[daveh]

Thanks I'm going to check to see if the vent is capped off.  You see I didn't install the tank and maybe the PO didn't install the vent tube.  Thanks for all of the great suggestions.  I'll fix it eventually.
Dave

[72rtchallenger]

It's a locking vented cap that goes under the flip top also where exactly do I drill it?

dont drill,,i have a 72 and it has about 4 or 5 lines coming off it and i use a locking cap under a flip top,,everything is new,except filler neck,,mine builds up pressure while driving and that is normal,,but after a day or 2 there is no pressure,,sounds like you have a vent line blocked