# Why does it seem like the second half of the gas tank goes faster?

Why does it seem gasoline goes faster in the bottom half of the gas tank

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The scienc-ey answer is because the level sensorâs output is not linear.

The less scientific answer is the sensor is a float that rides on top of the gas. The float is attached to a swinging arm that is about level with the ground when full and droops more from 1/2 tank to zero than full to 1/2. Plus the manufacturer wants you anxious to fill up the tank so it doesnât run dry and suck up trash from the cheapo gas station many use or burn out the pump running dry.

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Thatâs the way they design them to work. Every car Iâve ever had has been that way.

If someone made one that worked in a linear fashion, youâd see more than the usual number of those cars at random places on the side of the road.

What prompted this question ?

Curiosity?

It does not just seem like that, it actually is like that. Every single car I have owned with a working gas gauge has done that. On every car I have owned if you fill up the car and drive until the needle is at half, if you stop and refill then, you will need a lot more than half of the stated capacity.

Why do they do that? I think it is psychological, how many times have you heard someone brag about their gas mileage by telling you how many miles they went on 1/2 a tank of gas.

On my â95 Suburban, there was about 1/5 of the tank above the full mark, so about 2/5 below the âhalfâ mark.

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Yeah the same reason it takes so long for the gauge to move off of full. In other words, its a gauge, not a precision instrument and only provides a reasonable approximation of the contents of the tank for a reasonable person. I never know how fast the bottom half goes though since I fill up again when I get to half a tank.

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It would cost a lot more to make a linear gauge. Aside from the physical gauge operating over an arc, one of the problems is that most gas tanks are not symmetrical these days. They are designed to fit the space thatâs left over, similar to the windshield washer or radiator overflow tanks. The design used today does provide the most resolution on the lower half of the volume- something everyone should be able to appreciate. I really donât care how much more gas I have over 1/2 tank but I REALLY care exactly how much gas I have left below 1/4 tankâŠ

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There is no cost difference to make gauges accurate The sending unit is a printed series of resistors on ceramic (on most cars). The resistor values are specified by the manufacturer for the output they desire. They want the car to appear to be getting outstanding gas mileage on the first half of the tank.

Youâre confusing accuracy with linearity. Regardless, there is definitely more cost in a custom array of film deposition values than a simple linear resistor value.