Help! I'm losing Gas!

[Gary (CLC 18197)]

When the tank is full on my '66 DeVille Conv I tend to lose gas from the vent tube.  I would think there is some sort of valve to prevent this from happening.  Any thoughts on what might be going on or what replacement part I may need?

Gas is way too expensive to be dumping it on the ground every time I come to a stop!

[Big Fins]

Not being a wiseguy, but the laws of inertia are at play here. There is no way to stop the fuel from being released, unless you don't fill the tank to the top.

Now if you can find a one way check valve that has very little resistance to it, you could use that. Or...plug the vent entirely and use a 'vented' gas cap.

Fins

[Gary (CLC 18197)]

So are you telling me that it was normal for these cars to have this condition when the tank was filled?

["Cadillac Kid" Greg Surfas 15364]

What is normal?  My 66, and just about every other one I have seen has this same characteristic.  It is a function of the "S" tube that serves as the tank vent.  Perhaps they tried something new that year.  My suggestion is that you don't fill the tank completely. Afterall, rules for fuel tank emissions, and vapor recapture were only something in the minds of the Engineers 42 years ago.
Actually, the main symptom of this system is gas leaking when parked on an incline, so if you are leaking gas after a stop perhaps you might look underneath and check your tank and all the connections for that leak.
Greg

[jaxops]

Not to butt in, but just a thought....I went through a lot of headaches replacing all of the rotted hoses on my car.  Your vent tube may also be deteriorated.  Just another thing to check, you know?