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excessive pressure any ideas??

3K views 6 replies 5 participants last post by  ScoTFrenzel 
#1 ·
OK before it is asked I did do a search and really no real solutions with great success or at least what I read. 67 camaro with modified gas tank cut 4 inches on each side welded up and filler neck moved to behind license plate similar to 69 fuel tanks. Did this to have exhaust exit in rear valance (bumperless of course) looks pretty sweet in my opinion. I'm using vented gas cap but I'm still having pressure build up of course when cap is cracked pressure is relieved. Matter of fact the car is motorless right now and I looked over at it and it was puddling fuel from line that was not plugged. Quickly took a vacuum plug, put in line then cracked cap and fuel leak stopped as pressure was relieved. It got to be 70 degrees here today I think reason for pressure. My concerns are constant expansion may weaken welds on tank, don't know??? Does anyone make a higher performance vented cap? If I drill small hole in cap then garage will smell of fuel fumes dangerous. Or do I possibly put vent tube in filler neck with check valve of some sort?? Can anyone help I know many people have had similar issues. Sorry so long winded. Thanks ahead of time.
 
#2 ·
neverfastenuff said:
OK before it is asked I did do a search and really no real solutions with great success or at least what I read. 67 camaro with modified gas tank cut 4 inches on each side welded up and filler neck moved to behind license plate similar to 69 fuel tanks. Did this to have exhaust exit in rear valance (bumperless of course) looks pretty sweet in my opinion. I'm using vented gas cap but I'm still having pressure build up of course when cap is cracked pressure is relieved. Matter of fact the car is motorless right now and I looked over at it and it was puddling fuel from line that was not plugged. Quickly took a vacuum plug, put in line then cracked cap and fuel leak stopped as pressure was relieved. It got to be 70 degrees here today I think reason for pressure. My concerns are constant expansion may weaken welds on tank, don't know??? Does anyone make a higher performance vented cap? If I drill small hole in cap then garage will smell of fuel fumes dangerous. Or do I possibly put vent tube in filler neck with check valve of some sort?? Can anyone help I know many people have had similar issues. Sorry so long winded. Thanks ahead of time.
Well, it either is going to be vented or not.
That new cap sounds defective. Vented should not hold pressure. So it WILL stink.

You might consider installing a tank vent and a charcoal canister that is attached to the intake manifold. GGEEZ just like the "smog" cars.
That is the only way I know of to vent it without fumes, just like the EPA mandated 35 years ago.
 
#3 ·
Its easy to confuse volume with pressure. Emissions caps are designed to vent anything above about 3 psi... but 3 psi in a 20 gallon tank will seem like a LOT more when you open the cap. On a good hot day, if I spin the cap off of my 96 chevy, there is enough exiting flow that it will gently push the cap off the neck into my hand, but that's the way it should be.

If the fuel was only dripping/flowing out of the uncapped line, chances are it was only a couple psi in the tank. Even 10 psi would make the fuel squirt all over the place.

I wouldn't worry about the welds.

If its a truly vented cap (like old-school pre-emissions caps) then I'd worry that there was any pressure. They're supposed to be fully vented to atmospheric.
 
#4 ·
It seems like you have nothing to worry about. :D

I have had engines out for long periods of time while they were being rebuilt. I have had to loosen the gas caps, to relieve the pressure in the gas tanks, to keep the vehicles from 'pumping' fuel out of the fuel pump inlet hose.

JMO

Stephen
 
#5 · (Edited)
stop and think a minute....

you likely have a lawnmower/edger/chainsaw/weed wacker/whatever in the garage with a fully vented cap on each,,,
does the garage stink?

the bigger danger with gasoline is "NOT" letting the fumes dilute/dissapate into the air!!!....

any pressure in the tank and a ignition source near the filler is asking for a "kaboom" when you open the cap....

you can limit the venting to "only" when hot by mounting a marine gas tank vent/check valve and hose to a open air/dissapation location....

normal mechanical fuel pumps wants/needs "0" vacuum on the gas supply to work correct so it has to be vented somehow...
(it is a "pusher" pump, not a "puller" pump at all)

carbed cars do stink in a garage due to the hot wet intake gasoline evaporating when you turn it off....
the fuel pump check valve only holds pressure on the floats check valves for "maybe" 15 minutes worth of carb cool down....
(with many/most of the off the shelf chain store pumps even when new)
 
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