TomB275

If the evaporative emission system is defective the tank can be partially collapsed from the vacuum and reduce the tank capacity. (I've seen it but it is rare.) More likely, you still have 4.5 gallons left in the tank. Even when the miles remaining is zero OEMs design for some fuel left in the tank. It's hard to get the tank sending units to be absolitely precise with complex molded plastic tanks. I knew a guy who regularly ran 10 miles below zero before filling up...just because he could.