Vented gas cap

[scottprop]

I have a 69 D100, that has no emission stuff at all on the engine. My gas cap says "pressure vacuum" which I assume means non-vented. I never thought much about it until I drove home one day, and was going to change the fuel filter. When I pulled the fuel line off gas came spraying out like a fire hose. I'm thinking I should have a vented cap on there, am I correct? Thanks

[Hobcobble]

I have a 69 D100, that has no emission stuff at all on the engine. My gas cap says "pressure vacuum" which I assume means non-vented. I never thought much about it until I drove home one day, and was going to change the fuel filter. When I pulled the fuel line off gas came spraying out like a fire hose. I'm thinking I should have a vented cap on there, am I correct? Thanks

If I'm not mistaken, Pressure/Vacuum means that the
cap is vented to allow for either a pressure or vacuum
situation. Yours might be plugged up though.
John

[OleRed66]

That's a pretty good seal. Shoot if I take a right turn faster than a crawl, and my tank is over 1/4 full, I get fuel spilling out the cap!

[wally426ci]

Me too!

[nfury8]

The non vented tanks require a vented cap. The caps should be vented one way,
so they don't build a vacuum and collapse the tank (seen it happen!)

A properly working vented cap will still allow pressure to build in the tank.
Why the pressure builds is a different issue. I have been chasing a pressurized tank
issue myself on my 70 Crew. I finally opted to add a vent to the tank, like my 71 has.
Adding the vent is easy, but pulling, cleaning and flushing the tank so you don't
blow yourself up when punching the hole and soldering is another matter!

I have seen vented caps with worn out check valves (which I think are just rubber flaps),
were the rubber had cracked and leaked, allowing fuel to slosh out.

[scottprop]

Well, to be on the safe side, I ordered an NOS vented cap. Thanks

[Hippy_Dave]

My local CarQuest had my cap on the shelf - It was like 6 bucks - chrome top looks just like it's supposed to - sorry, forgot the part #

[elacruze]

My local CarQuest had my cap on the shelf - It was like 6 bucks - chrome top looks just like it's supposed to - sorry, forgot the part #

Yup, just bought one myself.

FWIW vented caps generally allow air in at near 0 vacuum, and vent outward at about 3 psi to prevent overpressure and potential carb overflow/hose failure/leaky seams.