lol - my car does the same - went through the same, voltage reg, airflow, earthing, different gauge etc. etc. I still think airflow is the cause, as per the thread Dr Mini linked above...
phillb wrote:
Mick wrote:
I hadn't sealed up the adjustment holes on the back of my gauges, and found the breeze pushing through from the engine bay via the gauge was cooling the bimettallic heated strip down. This made both the temp gauge AND the fuel gauge drop as speed picked up. I hadn't considered this before, but noticed that air whistled through my gauge bezels as I drove along... (This only affects the very slow moving gauges as opposed to later magnetic gauges by the way)
I discovered that if I wound down my drivers window (esp in winter) the gauges dropped, wind it up and the gauges rose. This was even with the adj. holes covered. Same reason, ....more wind drew past the gauges with the window down.
They can be very sensitive but very accurate when supplied with a steady voltage and calibrated correctly.
I just ignore it. I usually know how much fuel the car has in it. If I stop and it's below the E mark, I find a servo and put some in.
Does your temp gauge do the same thing? It used to do it for my temp gauge too, but when I injected the car I needed a different type of sender so I made a servo driven gauge
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