There is a very common problem where you are driving with say, 1/3rd of a tank (or any other amount of fuel), the gauge just drops to empty. If you drive long enough, sometimes the gauge comes back, sometimes not. I also have other issues where I will fill the tank and when I start it up, the gauge reads zero or half a tank but then will slowly creep up and reaches full after 5 minutes of driving. As Manny will inform you, the problem is a buildup of sulphur (???) on the rheostat so the resistance reading is either wrong or missing. Sea Foam helped me with both these issues for a while.