Fuel Cap

[venomouscamaro]

I am looking at grafting a motorcycle gas cap onto my car but the cap is vented. Are the stock 68 camaro gas caps vented or not vented? What is the big deal about having a vented or non-vented gas cap?

[Matt@RFR]

The big deal is to make sure you have the tank vented.

And to answer your question....you can NEVER vent a fuel tank too much.

[venomouscamaro]

Out of curiousity, what happens if the tank isnt vented? It makes me wonder because I dont believe my mother's 69 has a vented cap and we havnt changed the cap since she has owned it.

[Matt@RFR]

As any liquid heats up, it expands, which will create pressure inside the tank. That can lead to fuel return problems if you have a return going to the tank. If the opposite happens and the liquid cools down from when the tank was open last, it'll create a vacuum as it contracts. Pumps don't like pulling against a vacuum at all.

Also, if your tank wasn't vented, as you use fuel, that would also create a vacuum. It wouldn't take much of a vacuum before the pump couldn't pull gas out of the tank anymore.

Trust me, your mom's tank is vented somewhere.

[toddshotrods]

I can definitely vouch for the need for some kind of venting for the fuel tank. I had inadvertently set mine up with a non vented cap and both other "holes" preoccupied. It would run for a bout a mile and stop. I thought I had a pin hole leak in the main fuel line so when I pulled a rubber section near the tank to replace the old steel line I got hosed! It was literally spraying gas like there was a pump in the tank forcing it out! I had to hold my thumb on it and holler for my dad to open the cap. A big whoosh when he did and the pressure on my thumb stopped immediately.

I replaced the non vented cap with a newer style vented cap and she runs great.