Vented Gas cap


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By lameyer - 12 Years Ago
I have gone through 3 or 4 vented gas caps on my 56 f100 none of which ever worked right, I took the "in erds" out of the last one, that was a big mistake! I have a stock tank behind the seat, stock fill tube. So what is the right kind of cap to look for?
By Ted - 12 Years Ago

You might check the top of the fuel tank and insure it has a separate vent line on it and the line itself is clear.  If it does have that vent line, then you should be using a non-vented gas cap.

By jrw429 - 12 Years Ago
I could not find a working vented gas cap. So I bought a cheap non-vented cap and then cut a small "V" slice in the rubber gasket that seals the cap to the fill tube. I was careful to ensure that the "V" would be at the lowest point when the cap was installed. Since you can put the cap on in two different clockings, I am careful at each fill replace the cap so the "V" remains at the bottom and not the top, where it would vent and also channel water into the tank.



Before when I slowly opened the cap at the gas station, I would have several seconds of sucking air as the vacuum in the tank equalized. Now that is fixed.



More troublesome, this past summer when it sat in the sun and heated up, the pressure in the tank would increase so much that gas would leak out. That is when I did the cap.



Note that this is actually on my 70 Bronco. I think the same would work with my 57 wagon, but I think the cap has a poor enough seal anyway that it doesn't need the extra vent.



(Ultimately I'd like to put in a proper emissions control with charcoal canister, etc. Some day...)
By PF Arcand - 12 Years Ago
Jim: Not sure about a 57 wagon's fuel tank setup, but the cars have a vent line & don't require a vented cap. However, it is possible for the line to be plugged. There have been one or two reports of that problem & in one case it was a mud dauber wasp trying to build a nest that caused it. My 57 car with a vented cap & line would smell in the garage in the summer, until I installed a non vented cap..
By lameyer - 12 Years Ago
There is no vent line on the tank, as far as I know those trucks never had them. I thought about putting a vent line in the rubber hose between the tank neck and filler tube. Do they make vent caps with different pressure ratings? I already have to throw some new paint on the rear fender, So I would like to figure it out before cruz'n season starts again. Thanks.