I dont believe the sender is the fault. If you open that fuel gauge you will very likely find the bi-metal responder has a bow in it at room temperature. That came from being overheated and probably happened when the previous sneder died. A lot of speculation really but zero resistance for any length of time will cook the bi-metal. Due to how that strip is attached in a angled slot of the needle, the bow makes geometery wrong and the needle moves a very long distance rather than a short distance. To just go in and straighten it again doesn't fix it either. The temper of the metal is gone. Also if the insulation on that winding is black it will crumble when touched so it really just cant be fixed.
