Although the tank is 18 gallon capacity, the amount they hold must vary by vehicle.
I looked back at some of my old (1980's) gasoline credit card receipts and found several fill-ups in the 16's to the low-17's.
Don't forget that back in the day before the electronics came in, like the old Tokheim pumps, the calibration from pump to pump and station to station was questionable. We had 2 Union 76 stations and the dept of weights and measures was out about twice a year to check calibrations on the pumps...we never had issues but they routinely "tagged out" pumps at other stations(mostly Arcos)for being off. All stations, in Cali anyway, are equipped with tamperproof electronics nowadays.
