This past summer I had an incident where the gas leaked from the filler neck area and I only had 1/2 a tank of gas in the truck.
I replaced the cap and problem stopped.
You do have to be careful with gas expanding when you fill the tank, but it still can leak at any level from a faulty vented cap.
I fill my truck on the way out
Half full and gas comes up and out of the filler cap? There has to be more to this story. Was the truck parked on a hill?
I can see it building pressure and the pressure pushing gas out at or below the fuel level but there is no way the gas would expand enough to
double its volume based on the tank design being discussed.
Gasoline expansion rate is about 2% with a 30 degree F temp. increase. Gasoline vaporizes at 140 F. Therefore there is simply no way it can double in volume.
