Fixing the Fuel Gauge - "Getting the Right Reading"

My E32 was terrible when I first got it for trying to judge how much gas was left.

Often, after about 2 minutes of highway driving, I would see the gauge drop from 1/4 full to empty (without the warning light) and the on-board computer range would get screwed-up along with it. I'd heard the sender unit could often "lose" a "sensor wire", and as the gauge seemed OK otherwise I was willing to poke around in the sensor to see what I could find.

I found cleaning my sensor fixed my gauge so it read correctly - and linearly - across the whole scale.

It turns out the E32 sender is based on

The float carries 2 contacts, creating a moving bridge between the sensor wires - the other ends go to the gauge. My problem seemed to be from the (very slight) varnish residue on the sensor wires - they're "wiped" by a pair of very lightly sprung contacts (BMW must have guessed that this light contact would cause problems, since the contacts are gold-plated). I cleaned mine with alcohol and the problem cleared up.

Also, be aware that battery condition & load will affect the gauge. Mine would vary by about two needle widths with all lights on to all lights off when the car hasn't been used for a week or so.... dirty plugs/contacts will also give a premature empty reading.

Here's how I cleaned it...