Are gas gauges linear?

Nonlinear and ...
Scaled to tank shape?
Biased toward the top?

Or is it all about psychology?

It is mt perception that every vehicle I have owned burned fuel very slowly until between 1/4 and 1/2 tank, then the fuel seems to run out faster.

What do y'all think?

Most fuel gauges are not linear.

Agreed.

On my Jeep CRD, there's at least a good 4 gallons of capacity above the full mark - more than that if I fill it up to the cap - and times I've went as much as 150 miles before it even came down to the full mark - picks up the pace some between full and 3/4 - rather slow from 3/4 down to 1/4 - then drops like a rock once below 1/4.

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Just say "NO" to Ethanol - Drive Diesel

Mitchell Oates
Mooresville, NC
'87 300D 212K miles
'87 300D 151K miles - R.I.P. 12/08
'05 Jeep Liberty CRD 67K miles
Grumpy Old Diesel Owners Club

A fair number are vertical, not linear.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Vertical is a direction, linear is an alignment.

ver·ti·cal/ˈvərtikəl/
Adjective:
At right angles to a horizontal plane; in a direction, or having an alignment, such that the top is directly above the bottom.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Yes? The second definition indicates it's an alignment with respect to the horizontal, in other words, a direction. "Linear" can be in any direction or in no direction.

I don't understand what you're trying to say.

Neither does he!

Seems like the linearity vs. non-linearity is a consequence of parameters attributable to the physical and mechanical dimensioning of any particular engineering exercise more than any say electrical characteristic, I wouls suspect that MB fuel level transducers are more linear in their output as most are gesigned and implimented in a vertical sliding configuration rather than a pivoted cantilevered configuration of many other transducers. Many MB's particularly the 80's vintage have their fuel tanks positioned in the vertical plane behind the rear seat as a saftey precaution as the core area of the space frame is less likely to be impacted than other areas. It's hard not to appreciate that attention to saftey engineering compared to say the Corvair, the Pinto, or the GM pick side rail fuel tank fiascos.

I should shave been more precise in my original question.

The imprecision is likely due to lack of knowledge -- I don't know exactly how a fuel level gauge works or if there are multiple designs.

What I meant was that my experience indicates that the needle passing across the face of the gauge seems to move at different rates across different portions of the gauge face. I wonder whether this is a psychological perception or a fact.

I never figured out why the increments in our MB fuel gauges are not evenly spaced.




Maybe they knew about this non-linear property and compensated for it by making the gauges this way.

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It could be either dependent on the transducer design and implimentation particulars, some are by design more linear acting than others.

But of course no implimentaion would be immune to any independent psychological aberration attributable to its observer!

I was just joking with Bot. I thought the uneven increments on the gauge was correlated with the fact that the markings are not sweeping a circle around the indicator.
The MB gauges I've looked at were just a float set in a tube measuring the height of the fluid in the tank. If the shape of the tank is not symmetrical, the float isn't measuring uniform usage as the level drops. The other factor is the orientation of the tank in the car. In the wagons the tanks are under the back section, flat and not very deep. That gauge is more vulnerable to fluctuations as the fluid sloshes around the large flat tank.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I had a Suzuki once that went down very fast for the first half tank and then slowed way down the the second half. Most other vehicles I've had behaved the opposite way. I have heard that this is done intentionally, but don't have any proof. I rely more on the trip odometer to know how much further I can go before I need fuel. My car is very consistent about being able to go about 470 miles between fill ups and my bike (which doesn't even have a fuel gauge) reliably hits the reserve between 180 and 190 miles.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

Bingo! Teutonic OCD all but guarantees it could not have occured accidently! 50,000 years of human evolution driven by spending five months a year sitting in a cave trying to survive the mean and lean season has consequences!

Thanks for noticing and bringing this to everyone's attention, it is so easy to overlook some of these most subtle examples of engineering genius!

My W124 had a rectangular parallelepiped tank (with curves an crimped on the narrow faces) that was set off-nadir if I remember correctly. With a float system I could imagine that the rate of change would be variable at the top and bottom while constant through most of the midsection. Maybe that's why the M-B gauge does not have regularly spaced intervals yet the intervals are symmetrical over the center? Does that make sense?