Calibrating the Fuel Tank Sensor

Fuel Sensor Unit

On our trip, we had occasion to remove the fuel tank sensor to inspect the tank for muck or foreign objects that may be obstructing the fuel pickup. While we were doing this, we decided to calibrate the tank sending unit. It is based on a float that adjusts a small rheostat (variable resistor) that drives the gauge at the helm.

We checked that the gauge registered properly at both extremes and at the middle of the range by laying the sender on its side, as shown in the photo to the right, then moving the float all the way up (gauge reads full), the middle (gauge reads 1/2), and all the way down (shown here and the gauge reads empty).

We then loosened the keeper screw that holds the wire to the float. Slide the wire in the holder, holding the sender unit next to the tank until the float is near the bottom of the tank while the sender is held next to the tank. This sets the Empty position.

Adjust Float Wire for Empty

Verify that the gauge reads Full when the float is near the top of the tank.

Verify Gauge with Float at Full

It may be necessary to bend the wire a little so that you get full range from Empty with the float near the bottom of the tank, to Full near the top of the tank. When you're happy with the travel range and the reading on the helm gauge, tighten the keeper screw on the wire.

We had several inches of the float wire above the adjusting screw, so we bent the wire so that it would fit into the tank through the mounting hole. Cutting it off will work too, just put a bend in the end so that if the keeper screw ever loosens, the float won't fall off in the tank.

When working on the sensors, we found that the sensor unit screws are not drilled in a symmetric pattern. It is a good idea to scribe a mark on the sensor top and on the tank to indicate its orientation prior to removing it. Otherwise, you get to play an alignment game to determine the position in which all screws will fit into their holes.

Our fuel gauges now read accurately and we can use them to tell when the tanks are full when refilling. More importantly, we know when the tank is near empty!