Ask An Expert: Faulty Fuel Gauges

In this instalment of Ask An Expert, we've been asked to help Adrian Fitch with a Bentley fuel gauge issue which has been causing him countless trouble and where the cause seems to be a bit of a mystery.

Adrian asks:

“I have a 1980 Bentley T2 which I have owned since January. Ever since I have owned it the fuel gauge has always read full when the ignition is on, irrespective of how much fuel is on board. I checked all the wiring to the sender unit, and that seemed ok. I then thought it at was just a faulty sender unit, so bought a second-hand one off eBay. This didn't fix the problem, so then I bought a new one. Again, this didn't fix the problem. To cut a long story short I tried 6 sender units and 2 new gauges, Still the same problem, the gauge just read full with the sender unit showing no resistance in the circuit. I then thought it must be a fault on the car. I checked the wiring from the gauge all the way back to the tank, and there appeared to be no faults. So just to make sure I ran some new wiring from the gauge back to the tank. Guess what? Still the same result. I have also bench tested the units and get the same result. I have consulted an auto electrician, and bench tested the units with him. The only way we could get any reading less than full on the gauge was by adding extra resistance in the circuit. This then seems to point at the fuel sender units not being manufactured properly. My supplier, a well-known Rolls and Bentley supplier, then supplied me with 2 OE parts from Bentley. A fuel sender and gauge. Before fitting to the car, I thought I would check them on the work bench. Again, the same result. Can anyone tell me what I am doing wrong?”

We spoke to Nigel from Shadow Vehicle Services to see if they could shed any light on Adrian’s problem.

“Bentleys have ‘4 in 1’ gauges which display fuel, oil, water and amps. Usually, my first port of call with a faulty gauge would be to check the sender unit but since Adrian’s used six different units I think we can safely rule this out as the cause. From the above, it seems as if Adrian has followed the logical steps to diagnose this issue by trialling new parts and even new wiring too.

It may be that the wiring could be going to the supplier rather than to earth though, which would explain the resistance issues he’s been experiencing. However, Adrian has taken all the steps I would take so all I can suggest is for him to take the car to a local Bentley specialist, such as ourselves, to check over the work he’s done as I think it will need some investigation in person to get to the bottom of it“.

Do you have any experiences with faulty fuel gauges? Do you have any advice or tips for Adrian? Let us know in the comments below and don't forget, you can still submit your classic conundrums by visiting our Ask An Expert page!

The information contained in this blog post is based on sources that we believe are reliable and should be understood as general information only. It is not intended to be taken as advice with respect to any specific or individual situation and cannot be relied upon as such.