Why the top fuel level bar lasts so long

[CTScott]

There have been quite a few threads in the past that discussed this, but here's a Mythbusters style analysis of it (fortunately, minus the large explosion at the end):

Today I am working on the range until empty and fuel level in gallons (or liters) features for my YarGauge project. I drained Crashy's fuel tank and then added 1 gallon (precisely measured with a one gallon laboratory flask) at a time while recording the data values from the analog to digital converter, which I have connected to the fuel level input to the instrument cluster.

I plotted a graph to see how linear (or not) the fuel sender value is in regards to the volume in the tank. From bone dry to the top of the filler pipe, I was able to put in 12.8 gallons. The ADC value stops changing at just over 11 gallons.

So, you can put just shy of two gallons more into the tank than the fuel gauge can measure.