Recently my 1954 Monterey coupe developed extreme rust in the gas tank. After searching all sources for a replacement tank to no avail I had to have a stainless steel tank made. The tank is fine but now I am having trouble with a new after market sending unit. The unit fits the tank fine as the stainless tank was made from the original pattern. With the car hot from running and the tank near full of gas it expands out the center nut on the sending unit. Could this just be a defective seal in the sending unit or has anyone else had this problem with a sending unit?
I think you have a defective seal in the sending unit. Assuming the tank is properly vented the expanded gasoline should simply go up the filler tube.