A while back I purchased an Auto City gas tank. It seems like I can only put 16 gallons of gas in it. What's up with that???
I'm thinking maybe an airlock in the tank. Mine's auto city classic as well..........seems like I remember putting over 18 in mine once. running on fumes, lol. Possibly the rake, or lack of with the car's stance?? I have a rake, and also I have 1/2" spacer blocks between the tank and underside of the car at the front of the tank. I needed to make room for fuel lines. I'm just thinking out loud here, but if your tank is somehow positioned low in the back, it could create an airlock at the front of the tank? Are you using the auto shutoff on the gas pump? Maybe try bouncing the car a little after the shutoff to get rid of an airlock.