I had a problem with a new cap that the inside vent got stuck. It created a vacuum in the tank and wouldn't allow air to enter to replace the fuel used by the engine.

In your case it seems to be going the opposite direction.

Did you fill the tank up all the way full up the filler neck? If so, the fuel probably expanded in the heat of the day and forced its way out the vent hole.

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)