Little bit of BS trivia for everyone. Call it an Easter gift for you.
The fuel level is measured by a simple float on the end of a metal arm as in this pic.
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The arm runs down the outer passenger side of the tank and the float is the round thing at the end.
Now, if you try to remove the fuel pump with 1/2 a tank or more of fuel, fuel will come flooding out that hole. As you can see, a considerable part of the tank is above the level of the fuel pump. At least 1/3 of the capacity, probably close to 1/2.
So if any level of fuel greater than 1/2 a tank fills the lower chamber to the brim, which means the float is jammed against the roof of the tank, how does the gauge manage to display a lowering level of fuel when the tank is, say, completely full. The float is jammed hard against the top, so it wont move until the tank is 1/2 full or less.
My only conclusion is the cluster guesses how much fuel is in the tank for anything over 1/2. Calculates the decreasing level based on fuel injected.
But back on topic... I found these old pics I borrowed from someone on the net ages ago.
There was a failure in the join around this white plastic bit.
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Which resulted in fuel leaking out when the tank was full. But only when the tank was full.
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As I said, hopefully not your problem.