VCCA Home Forums TECHNICAL - 1945 AND NEWER 1965-1970 1969 impala drains its gas tank

1969 Impala, 396, new gas supply from cap to top of manifold.
Car was sitting in car port and within one hour dumped over
15 gal gas on the drive.. had not been run for a week..
Hauled to garage who installed gas supply parts. The new vent
was extended about two inches up from where it was..
Set car in the sun and it did it again.. Appreciate your
response, the shop is having trouble with this.

Roy,
As you know, if there is a leak in a gas line below the level of gas in the tank then the liquid can be siphoned out of the tank. Otherwise it takes pressure.

Apparently something must be plugged up creating pressure in the tank and when the gas warms during the day forces it out. Is the gas cap vented or seals and the tank has a vent tube? Where does the gas exit from? Out the vent? If so does the vent line extend down into the gas tank or just to the top of the tank?

If not out the vent could a dirt dobber have plugged it and then pressure force gas out the fuel line to carb or past the gas cap?

The shop owner is now trying to consol me and answer how a
vent can hold enough pressure to push gasoline our the vent
tube at a rate of over 15 gals an hour but will not vent the
air that created the pressure.. At this time a replacement
for the new replaced vent assemble will be installed..
Thanks for your contribution Chip..