Series 3 Fuel gauge rollercoaster

Hi All,

I've got a 1981 Series 3 Diesel which has, until very recently, had a non-functioning fuel gauge. I finally got around to having a rummage the other day, pulled out the sender - and found it had seized up. Gave it a good clean and put it back, and now it's showing an (almost) full tank. Great.

Except that the reading fluctuates like mad on hills and around corners. I can go from reading 3/4 full to stone dead empty in the space of 60 seconds up a hill, before it will gradually climbing back up on the flat. It's all over the place, and fluctuates very rapidly, which can make for some thrilling drives when I'm not sure how much is left in the tank.

Does anyone know if this is a voltage stabilisation issue? A problem with the sender? Or a problem with the gauge or instrument cluster? I've already run a separate earth from the sender to a good earth on the car, so I don't believe that the problem is earthing of the tank/sender.

Any recommendations for things I can try (or indeed, just things I should replace) would be much appreciated.

Mine can do this, I think the wire is loose behind the binnacle because when I push around the washer pump it comes back down to where I filled it.

Thanks for your reply - that's really interesting. If this one is being caused by a loose connection I can't quite find it, so I'll keep digging. I know that the gauge reads the variation in resistance from the sender, but it seems to be varying much too fast. I'll keep looking.

I've double checked the wiring behind the instrument cluster and everything seems to be fine - current is passing as expected and the connections look solid. If anyone else has any ideas about what might be causing it to be so wayward I'd value the insight before I just start replacing random bits. Thanks!

Try a new sender and if that doesn't work a new gauge?