I just started to drive my 72 cutlass again and drives without a problem.. but when i went to fill the gas tank i noticed it only took 10 dollars and it overfilled and spilled.i know there was less than 5 gallons in the gas tank.any ideas? thanks.(i cant tell how much gas i have cause the sending unit is disconected from the gauge..) i tried filling it with a gas can and it was filling up without a problem.im thinking it may be the vent hoses.

 

I cannot think of what could cause that issue unless there is gas that crystallized on the bottom of your tank. That would take up space in your tank and not allow you to fill it to capacity. Your probably going to need to drain whatever gas you can get out if it and drop the tank to investigate it further.