Yes, that's due to the floater. It floats so that part of it is above the level of the fuel, so as you're filling the tank, it will touch the top of the tank before the tank is actually 100% full. Then, as you use the gas, the gauge registers full until you get below that point again -- basically, F on your gauge means "the floater is touching the top," rather than actually "the tank is full". When you get into the lower "half" of the tank, it falls more quickly because the bottom of the tank isn't flat -- it slopes toward the outflow pipe, so that the gas flows from the tank into the pipe even if your car is headed uphill and the tank can drain completely, and therefore the same unit drop in volume causes a greater unit drop in floater height, which is what the gauge is actually measuring.
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Date: 2011-03-08 08:47 pm (UTC)