Gas Gauge Accuracy

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Chzman
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Location: Idaho

Gas Gauge Accuracy

Post by Chzman »

My fuel gauge seems to be inaccurate. I have about 150 miles on a full tank, reset the ODO when I filled up, but the gas gauge says 1/4 tank left. I know the big 6 gets questionable mileage, but this sounds extraordinarily low MPG.

Is the sending unit in the tank responsible for the reading on the gas gauge? If I take the cluster out, is there a way to show the calibration on the gauge, or do I need the sending unit out of the fuel tank to check it?

I bought the car from a friend and she did not tell me much about the operation of the fuel gauge, or any other questionable gauges. Discovering issues is expected for a sub $1000 car!
Thanks,

Chuck Jenkins
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1968 BMW 2002
1977 BMW 320i
1989 BMW 635CSI - Last 7 = 3268048
Got all 3 decades covered...
quadrajet
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Re: Gas Gauge Accuracy

Post by quadrajet »

I have the same problem with my gauge. Mine is a real guessing game, as my odometer is inoperative at this time.
I'm not brave enough to go until the low fuel light comes on. I'm assuming the E24 has that feature..
89 635CSI, 91 318is, 91 318ic, 99 525iT(84 325e, 85 325e, 87 325is,91 325i, 88 325, 86 325e, 3-91 318is, 88 535is, 84 633csi, 86 528i Euro, 97 528i, 98 528i, 98 318ti, 99 525i past vehicles)
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86_6series
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Re: Gas Gauge Accuracy

Post by 86_6series »

Yes, the float is in the tank #9.
https://www.realoem.com/bmw/enUS/showpa ... Id=16_0014

Yes, there is a light IIRC on the left of the fuel gauge.

I've owned my 86 for going on 34 years. Average MPG around 20. Long trip with cruise control 26 plus.
With the rebuilt 265 HP motor-long trip cruise control now 22 MPG.
86-635CSi
96-MB C220 SOLD
98-740i
71-Continental MK3
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RossDinan6
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Location: SW FL, USA

Re: Gas Gauge Accuracy

Post by RossDinan6 »

Not that I have ever trusted a fuel gauge. The fuel gauge is not linear. I see the level drop faster in the bottom half than the top. The tank is not a cube, so the gauge is relative. As stated above, there is a low fuel light. Don't run around on it for too long.

Clear the trip on every fill. That way you know exactly how long the tank will last (well if one pays attention). This, of course, requires a functioning odometer.
Ross
'84 633 Dinan turbo
Pod
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Re: Gas Gauge Accuracy

Post by Pod »

When I bought my first E24 back in 1993, I was amazed when it ran out of petrol the first week I owned it when showing 9 miles’ range on the OBC 😂
songzunhuang
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Re: Gas Gauge Accuracy

Post by songzunhuang »

Is the gauge "jumpy" or does it always register low? If jumpy, you should take the cluster out and clean all the contacts. I just lived with a jumpy gauge for over 5 years! Finally figured out it was the connections in the cluster. I replaced the sender unit earlier and it wasn't the problem.

You can take out the sender unit from the gas tank pretty easily and test the resistance. I've got pictures of that in my post on page 10. viewtopic.php?f=25&t=25858&start=225

In any case, if you do think it's your sender, I have a perfectly working spare if you are interested.

Also, the reserve tank light is on a different circuit than the fuel level. I've had the reserve light come on when my gauge was showing 1/2 full. I ignored it once at great peril. I had to call AAA and get gas brought to me. At $72, it was the most expensive 2 gallons of gas I ever bought. Pay attention to your reserve tank light. Also my OBC was reading 30+ miles when it died. Since it relies on the fuel level for calculations, I'm guessing it was messed up and linked to the gauge.

For almost 6 years now I just reset the trip meter and I know that when I am at 275 miles I should start looking for gas. Now that my gas gauge is working well, I'll be watching it's behavior closely. Jump to page 35 or so of my posts and you can see how I cleaned the contact posts for my gauge. Good luck.
-----
Song Huang
1984 633CSi
Last 7 of VIN: 6997383
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