Gas tank venting

mbalbritton

mbalbritton

#@$%!
Joined
Mar 22, 2005
Location
Lakeland, FL
Ok so a vented gas cap let's air while not letting fuel get out, right? Why is it that the tank on my 1967 dodge d100 become positively pressurized. You go to take the cap after it's been sitting and it blows fumes and mists gas out of the tank?
 
vents plugged on tank....in my opinion.......FWIW. probably takes fule slowly at the pump too?
 
no, fills just fine. This is an old school tank that fits behind the bench seat inside the cab. short 6-8" filler neck, hole hose going from pick to carb. no return line, and the only vent is the vented gas cap and it's a brand new locking cap that works fine.
 
so IOW there is no charcoal canister? I think all gas caps are required to hold pressure.. vented cap means it will relieve a vacuum..
 
a_kelley said:
so IOW there is no charcoal canister? I think all gas caps are required to hold pressure.. vented cap means it will relieve a vacuum..
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This. It will only allow air in as the fuel gets pumped out to avoid collapsing the tank or causing drivability issues.
 
rattlecanpaint said:
This. It will only allow air in as the fuel gets pumped out to avoid collapsing the tank or causing drivability issues.
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Yep, older trucks usually had a warning of pressurized tanks spraying fuel when opening.

Usually not an issue unless it's hot out, if you drive to say the gas station, usually the fuel pump has pulled enough fuel out to equalize the tank and no long be positively pressurized.
 
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