hi sages- whenever i think i know a ton of stuff about sl6 a bodies and f bodies, i run into a new encounter. been running around in my 80 sl6 volare wagon . at the gas station today when i took off the cap( tank was almost empty) i noticed a big inrush of air as if there was a vacuum in the tank. i filled the tank and drove home(a few miles) . in my driveway i removed the cap and noticed the same inrush of air. never experienced this before in the other f bodies or a bodies i have had. the feather duster never does this. otherwise the volare runs fine and starts normally. the cap is the original, appears not to be vented and has a rubber seal which butts tightly against the nozzle. is this normal or is something needed like a vented gas cap. your advice is appreciated. bob f

im not an expert on this, but if your gas cap isnt vented then id say its possible that is were the air is coming from. maybe someone else can clarify.

Tank should be vented through the charcoal canister. Check to make sure the line and canister aren't plugged.

~THOR~

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1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing

Your fuel cap is a pressure-vacuum type. It has a two-way spring-loaded valve in the middle. The "outward" valve allows serious overpressure to vent off (the primary vent for pressure is via the charcoal can). The "inward" valve allows air to prevent a vacuum forming in the tank as fuel is drawn off. I'm guessing your cap's "inward" valve has failed, clogged, or stuck. You'll want to fix this in a hurry before your fuel tank collapses. Unless you're unlucky, the fix is as easy as a new correct replacement fuel cap.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

hello sages- following forum advice from dan and others , i tried 3 different gas caps over a week. all had what looks like a rubber bubble with a nipple in the caps center . guessing the two way spring valve is inside which is what dan mentioned. i did incorrectly state what was happening though. when you remove any of the caps after driving, air pressure whooshes out, not vacuum sucking air in. unlikely that all my caps are bad. moe says an outrush of air pressure is normal and common to cars since the 70s. says the air pressure/vacuum valve only releases when the pressure/vacuum becomes too high which is rare. the caps have a warning on them which says to remove slowly due to pressure/vacuum in the tank(normal?). surmise dans analysis was correct. moes corollary makes sense too. what say you? thanks bob f

Outrush of air is not normal. Find and fix the problem with the tank vent system. It'll be somewhere between the tank and the charcoal can.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

i've noticed on my 64 there is a rush of air out also when i fill up with gas, but i have no charcoal filter on this. What would cause the pressure buildup?

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64 barracuda
64 valiant convertable
65 valiant sedan
65 signet
74 vw beetle convertable
79 E-250 4WD van
94 dodge dakota

Your '64 should be vented through the gas cap, if it's blocked, or is the wrong one, then that will happen. It's the same thing on a portable can left out in the sun, or if the temperature is high where the container is stored. The fumes from the vaporized fuel have nowhere to go, and create excess pressure inside the container.

Makes it a real pain to get the cap off during the hot summer months...

~THOR~

_________________
1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing

64s don't have a vented cap.

There's a vent line on the fuel filler pipe near the top, next to the cap.

Open the trunk, and you should see the vent line.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Ahh... so if the gasket is the wrong diameter (too wide) it can cause that to happen?

~THOR~

_________________
1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing