Fuel gauge sender

The fuel gauge and fuel light are controlled by a sender mechanism in the tank. This sender does three things:

1. Gives a reading of the amount of fuel in the tank (obviously).
2. Closes a contact to operate the fuel light when the tank is nearly empty.
3. Provides ‘mechanical damping’ to stop the readings fluctuating wildly as the fuel sloshes around.

So if you have trouble with any or all of the above, the sender may be suspect.

On my car, the fuel gauge was waving around all the time, and (even more annoying) the fuel light would come on under hard acceleration.
You can get at the sender from inside the boot. Just remove the cover, detach the wires and turn the sender assembly 1/4 turn anticlockwise to release it. If the tank is full, be prepeared for a lot of fuel spillage.

The gauge float is inside a housing which has a small hole in it. This means fuel can only flow in (or out) slowly, and keeps the reading steady. There are also a couple of large ‘plug’ holes at the bottom which are plugged during manufacture. I found that one of these plugs had fallen out, allowing fuel to flow in and out rapidly, giving an erratic reading.

I plugged the hole with a suitable piece of plastic. I originally held it in place with epoxy resin, but the glue went soft and the plug fell out again. It is now held in place with a small bolt and nut, and the fuel gauge and light work correctly.

Things to note:

• It is possible to dismantle the sender to see how it works, but it is incredibly difficult to get back together again. If you do dismantle it, check that the float moves up and down smoothly, and that it works properly before refitting it.
• Be extra careful not to weaken the plastic clips holding it all together. I found that the gauge popped apart a couple of times, before I fixed it properly with some tiny screws to hold it together.
• There is a small screw at the bottom which allows you to adjust the calibration of the gauge and also set the point when the fuel light comes on.
• Be very careful to refit the tank seal correctly, otherwise you will get petrol fumes inside the car. Examine the seal carefully: the inside ‘lip’ should be uppermost. This lip engages in a recess on the sender. If in doubt about the condition of the seal, replace it.

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