Quote:
Originally Posted by 68caliRat
The vent's purpose is not to allow the free exchange of air from the tank, but rather to allow air to escape as you fill your tank, or enter as the fuel is used. Modern vehicles have a system that traps the fuel vapor and returns it to the tank while still allowing air to enter or leave the system, while fueling. That vent is supposed to be hooked up the tank filler to allow the gas station's pump to trap the vapor as you fill up. Otherwise air gets into the tank through the gas cap. As fuel is used the negative pressure opens the valve in the gas cap to allow fresh air to enter the tank keeping the inside and outside pressures equal. I'd just cap it, or hook it up as designed right to the filler next to the cap.
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Ummm.... not true. The vent's sole purpose is to ALLOW air to enter to enter when there is a vacuum created in the tank by the fuel pump draining it AND to allow air to be displaced when you are filling the tank and the fuel is pushing the air to go somewhere.
Old car systems just vented the tank to the open air, which gives you the wonderful smell of gas if kept in a closed garage. Back in the 60's and earlier, a lot of homes did not have closed garages so it wasn't a concern.
Getting into a more modern system of the 70's, they started using charcoal canisters and vacuum tubing up to the carbs, to help draw the fumes into the engine and not vent into the air. It worked okay but still on hot days, the fuel in the carb would actually off gas and you would get some smell, not as bad as an open system though.
Now modern cars started using vacuum systems that would purge the systems into a closed loop setup, which never actually allows the fumes to vent into the air. This added a lot of complexity to the systems but they worked great. No more fumes.
In CA, they started testing these newer systems and you will fail a smog check if it doesn't pass the test of the evap system. All it takes is one vacuum leak and the system doesn't work.
In your case, you are going to need to vent the tank into a charcoal canister to really have any chance of gettting rid of this problem. Other methods, like longer vent lines, check valves and such will help some but not 100%.
My .02 worth.