When filling up gas in a car why does the first notch at full take the longest to go down, then all subsequent notches go faster?
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You are overfilling your tank (as far as the sensor is concerned) so you have to burn down to the sensor before it can start accurately measuring how much is left.
It varies by car, but it’s often due to the shape of your gas tank. It sounds like yours is narrower at the bottom. A simple float gauge only measures the level of the fluid and not necessarily the actual volume.
On top of the other answers I’ll add that small changes at the bottom of the range are much more important than changes at the top. That means that a non-linear scale is actually quite helpful.
Because it’s too expensive to make a full-range linear volume gauge, especially considering the irregular shape of most gas tanks. This is so difficult that even expensive airplanes don’t do it. They rely on flow meters instead. In fact, I recall the old rule on gas gauges in light aircraft basically gives up entirely on this issue – it only required that the gauge read empty if the tank is empty. I.e. It would have been acceptable to cover The gauge with a card reading “empty”.
There’s a linear sensor in a tank that isn’t rectangular. Ultimately it’s not worth the time to engineer a sensor that accurately accounts for the curvature of the tank. Much easier to make one sensor for the whole $Brand fleet and use it no matter what shape and size the tank is.
The sensor is probably (I’m guessing) designed to produce very accurate readings for the brand’s flagship car. Every other model gets “good enough.”
The fuel gauge is connected to a float in the gas tank. As the level of gas goes down, the height of the float changes, which causes the gauge to change.
But they’re not always calibrated perfectly, so the top gallon or so of the gas tank may be above the gauge’s range, so to speak.
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