There are two options for fuel quantity senders. The first is to use a float that reads the fuel level with a hollow plastic float on the end of a wire that sits on the top of the fuel in the tank. The position is read through a resistive mechanism. This is a well-proven design but has a few drawbacks. The other option is a capacitive fuel sender. This has no moving parts and can measure from the first few ounces in the tank to the last few. The only disadvantage that I’m aware of is that it must be re-calibrated when you change fuel types. Since I don’t plan on doing that much (if ever), this is a non-issue for me.
The capacitive senders require mounting two electrically isolated plates in the fuel tanks. The capacitance between these plates and the tank is measured by a small AC signal. The fuel acts as the dielectric and changes the capacitance. Once calibrated, this system is easily accurate to a tenth of a gallon.
The first thing is to cut some plastic tubing to length.
These slip over the screws (after putting on a large countersunk washer)…
…and through a UHMW washer…
…and three more UHMW washers on the other side. As you can see, the screw can’t possibly come in contact with the rib. This is what keeps the plates isolated from the tank.
The screws thread into nutplates that are mounted to the capacitive plates.
Here is one of the plates after mounting it to the rib. The two outboard plates have to be modified at the bottom to clear the stiffeners.
