When you drive, the fuel sloshes around, making accurate measurement
difficult. To counteract this, the fuel gauge will react to change very
slowly. As you drive, a higher peak level is seen. After car is off, a new
lower level will be displayed and the fuel is not sloshing around. I have
seen this same thing in several cars.
Now when I turn the key off on the Granada/Sovereign/PTCruiser the fuel
guages all read zero after a few minutes.
Are you actually expecting a reading all the time? if so then maybe the
alternator is overcharging or the battery is getting tired.
As long as it ain't leaking and you're not losing fuel then it's not costing
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