"Why do you believe there is air space at the top of the tank? IF the filler neck on say a 68-70 Charger is full of fuel, how could there be an air space ?"



i have screwed up filling up my charger till the fuel ran all over the quarter, and out the vent line [which dumps into the frame rail] making a real mess.
i don't think there was any air that time. [sure stayed on full for long time.]
however, that was tons of years ago, and i'm super careful these days filling it up.
also, the mess was during the time i had the original tank and sender in it.