I have a universal 15 gallon gas tank in 31A. When I fill the car up, gas comes leaking out the vent tube under car. I feel that the gas must be expanding from temperature difference. If you unscrew the filler cap it stops from leaking out of vent tube, when you tighten the filler cap tight it starts leaking out of vent tube. Drive the car a mile or so and it stops. I have 1400 miles on the car since finishing a two year project. Can't believe I haven't caught on fire. Just noticed today there was gas under car at service station. What would be a safe fix?
The vent tube needs to run up and above the tank and filler neck (If applicable) in a loop before it exists the body.
When I got my O.T. '66 VW tank back from the radiator shop after they boiled it out, I didn't notice the 6mm. tube that is silver soldered into the large fill tube. Idiots crimped it flat with channel locks or some curved plier... At a glance, it still had what appeared to be the same cross section...BUT it was crimped horizontally, so it was NOT visible. Until I went searching for the reason it was 'running out of fuel'... Clever young wife went at the crimp with some 90 degree picks, and fashioned another tapered tool, opened it back up in 'no time'! (an hour...) Grrrr...
That's the "tank vent to let air in when you take fuel out" that is used in place of a vented cap. You can run the hose up front to a charcoal filter, run a hose up to where the breater or top of the hose is higher than the filler. This showing the roll over valve that mgtstumpy showed in the lower right corner of post 4. The vent hose up to the top of the filler neck doesn't vent the tank to the outside it lets air out of the tank when fuel goes in without having the fuel barf back on you like it does on some righs when the air coming out of the tank wants to push the fuel back. When you fill the tank you have to let air get out of the tank easily. When you drive down the road you have to let air in through a vent to replace the fuel that is pumped out or you create a vacuum. That vent can be a remote vent or a vented cap.
Thanks for all your help. I'll try moving the vent tube higher. It seemed odd that the fuel stops leaking out went the filler cap is off.
So, when mounting a fuel tank in trunk on Model A, how does one mount the vent hose and rollover valve above the tank and not fill the trunk/interior with gas fumes from said vent? Is this vent only allowing air in to displace the fuel ****ed out from pump and therefore not allowing the fumes to come out?
If fuel is coming out of the vent with the cap on, the vent line inside the tank is submerged in fuel. As the fuel expands, it goes out the vent tube. If the tube was above the fuel line, only air would escape. You are either over fueling the tank, or the vent tube is to long. It won't matter how high you raise the end of it, the pressure will still force fuel out as long as it's submerged. Roll over vents have a check valve that prevent fuel escaping when turned over, other wise they are open to allow air in and out. A hose will be needed to vent to the outside of the vehicle.
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