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Zeke · 07-25-2010, 08:16 AM

Might be wrong but pretty sure it stays in the tank until you take the cap off, outside temp changes or use gas driving.

Even new cars don't vent to the outside that's why you get a woosh sometimes when you take the cap off. The canister on the 71-72 tanks and newer vehicles have canister to hold the gas vapor until it can be sucked in by the engine. The newer vehicles have a fill vent because when they went to unleaded gas they made the filler smaller to keep people from filling with leaded gas. Some gas stations have nozzles with contraptions, California, to suck up the fumes while filling up.

If you can blow both ways on a vented cap you probably need a new one.

07-25-2010, 08:16 AM	#2
Zeke Active Member Join Date: Jun 2002 Location: L.A. Lower Alabama Posts: 453	Re: How does a gas tank vent? Might be wrong but pretty sure it stays in the tank until you take the cap off, outside temp changes or use gas driving. Even new cars don't vent to the outside that's why you get a woosh sometimes when you take the cap off. The canister on the 71-72 tanks and newer vehicles have canister to hold the gas vapor until it can be sucked in by the engine. The newer vehicles have a fill vent because when they went to unleaded gas they made the filler smaller to keep people from filling with leaded gas. Some gas stations have nozzles with contraptions, California, to suck up the fumes while filling up. If you can blow both ways on a vented cap you probably need a new one. __________________ 1969 C10 350 3spd 1995 GMC 3500 XC 350 dually When Thomas Edison worked late into the night on the electric light, he had to do it by gas lamp or candle. I'm sure it made the work seem that much more urgent. George Carlin Last edited by Zeke; 07-25-2010 at 08:18 AM.