Fuel gauge reading odd

[Grrrmachine]

This is an interesting one. I fitted a new 63 litre tank, and stuck plenty of fuel in it - around 30-40 litres, and the gauge read 30+ litres. Now I've driven, the gauge dropped alarmingly, and is now well below the warning light area despite the light not coming on, and the car still driving. I've driven about 150 miles.

Thinking this is dodgy, I unplugged the connector by the tank vent hoses, and bridged brown-green to earth, and the needle only went up to the 20litre mark. Bridging brown-grey to earth made the warning light come on, so that works.

Clocks are the same as the car always had, and I'm getting a total resistance on the wire of 50 ohms, although I've not tested each gauge individually. Even the brass nut is tightened up properly.

Is there a chance the gauge itself is broken?

[TPS]

I had the same problem after changing clocks, turns out I had a 55 L gauge & a 63 litre tank, swapped the old gauge from the faulty clocks, solved it.

The gauge would be showing half full, after it was filled up, wasted money keeping on filling up!

[Grrrmachine]

As I said, these are the original gauges. 18 months ago all was working fine, but since then the car's been "restored" which included a new fuel tank (same size) and new SI batteries. I can't believe either would affect the gauge, but you never know.

Plus, bridging the wire makes it read significantly less than half.

[Speedtouch]

If the gauge only goes half way up when you earth the sender connection, then yes, there is probably a fault with either the gauge, or the cable leading to it.

[Grrrmachine]

Hmmm. I'm wondering if I damaged the needle during disassembly to repair the SI board, but that wouldn't explain why it read over half two weeks ago, and now won't.

[Grrrmachine]

So before I buy a replacement gauge to test, is there anything else I can check?

[jmc330i]

the gauge dropped alarmingly, and is now well below the warning light area despite the light not coming on, and the car still driving. I've driven about 150 miles.

The gauge in my Sport reads like this. At full, the needle is only just over the 3/4 mark and there's no more fuel getting in there! Only once did the light flicker on, even when the needle has dropped well below the light itself, so much so the needle hardly moved.