Fuel gauge mapping

[ettlz]

Has anyone figured out the mapping between the markings on the fuel gauge, and what's actually in the tank? (Otherwise I'll have to try borrowing my parents' Up! PID...)

[Tom_I]

By all accounts the fuel gauges in these cars are very non-linear in their readings. I don't know why. With the sort of technology available these days, you'd think that they could devise something which could tell you how much petrol you had with reasonable accuracy, but apparently not.

 

Personally I can't be bothered to worry about it too much. I tend to fill up when the needle goes below a half on the gauge. At that point the tank should take 18 or 19 litres, but usually takes between 23 and 25. I certainly wouldn't let it get too low!

[ettlz]

I've had an idea. I'm going to start making a record at partial refills of needle movement versus what's delivered by the pump. If I get enough these samples across the gauge's range, I should be able to piece together the gradients into [an approximation of] the calibration curve.

[MikeW]

All i can say is i try to brim mine, It'll go for up to 100 miles without the needle even moving, then it moves down quickly.

[Markyg]

All I know is that I drive 400miles then fill up.

[MickA]

If I had a car like my old 2.5lt Omega I would be worried by petrol consumption. The reason I have no such worries now is the Citigo, once you get the general mpg and the knowledge of how the gauge drops quicker on the last half of tank than the first half, just fill and drive, and repeat.

Life's too short to worry over at what point do I have a set amount of fuel left etc. And to add the PID isn't that accurate, it just tells you that you are running out of fuel quicker on the second half of the tank. A PID borrowed from another car will only work correctly in the car it was registered for.

[EikokuSanzoku]

It's like reverse expotential....... nothing ..... nothing..... then all gone.

[learnwithmike]

having seen this thread, i have noticed about 80 miles without movement and then about 20 miles per marker down to 3/4 tank. i would guess that a physical 1/2 tank of fuel is displayed at the first or second marker below 3/4 on the fuel gauge. i usually fill up when the fuel light comes on and fill to the pump shut off.

[ettlz]

I have my first solid data. From 0.25 to 0.6 on the gauge is 10 litres. (I would've gathered more, but I suspect visiting four petrol stations over 30 minutes and putting 5 litres in at each would trigger a block on my credit card.)

 

(Based on what I've seen so far, the gauge shows roughly the first 30 litres.)

Edited 16 March, 2014 by ettlz

[ettlz]

Here's the first best-fit curve for my CitiGo so far:

 

 

It's currently a quadratic curve derived from a least-squares fit, based upon 3 visits to a petrol station. I'll up the degree to cubic once I've more data.