Reply from VDO - MB fuel gauges
 

I'm convinced that there is a defect in some MB fuel gauges. In all three MBs I've owned - 1971 250, 1977 280E, 1989 300E - the fuel gauge has had the exact same problem. It shows full to half fine but from half to empty, the gauge dances around. The low fuel indicator light is constant and works well (that, combined with my trip meter is how I measure my fuel consumption). I find it odd that all three cars from over 3 decades have the identical problem!

I've checked the sending units in the tank, with advice from this forum, and they've all been squeaky-clean. The floats slide perfectly. In one case (the 280E) I replaced the sending unit and still had the problem.

I recently contacted VDO with a description of the problem and here's the reply -

Hello Chris ,
we here are not aware of any problem with the MB fuel gauge . However if you need service to be done , please check with our service centers here :

http://www.vdona.com/Tech%20Support/repairpage.htm

these companies may find something in you cluster .

Mit freundlichem Gruß/Kind regards

Klaus P. Bornhaeuser
Manager Technical Support
Siemens VDO Automotive AG
188 Brooke Road
Winchester,VA.22603
Tel. 540 678-XXXX

I'm still not convinced. A thread in this forum mentions that re-soldering the cold solder joints in the back of the gauge in the instrument cluster can fix the problem. That will be my next step.

Still, I remain convinced that these gauges have an inherent fault. I've never had a problem yet with the oil, tach, clock, speedo, etc. Even the "economy" gauge works well. ;) Too many people seem to have this same problem..there must be something to it. Anyway, I'll see how the soldering goes...

Zeus, I wholeheartedly agree with you!!

The fuel gauge sender in my mom's 97 E320 had to be replaced under warranty.

The fuel gauge in my 97 C280 occasionally gives the wrong indication, but works most of the time, I strongly believe that the problem is with the senders (two of them in the tank). I'm not too worried, though. When it does act up, usually once per tank of gas when the tank is around half full, it dances around and gives wrong indications for no more than 30 seconds. Although it has not done so in about a month.

I agree with you that there must be some type of common problem with them. When I called the dealer to get a price quote, they said they have plenty of them in stock, as if it such a common repair that they know to keep a stock of them.

I had the same problem on my 87 420sel and it was the fuel sender unit. It is easly repaierd, thank god cuz a new one was over $100. Remove the sender from the tank. Open it, and you will find a float that mover a shorting bar between two small wires. These wires act as resistance elements. The shorting bar slides up and down along the length. The resistance changes and the guage moves as a result. The problem is that the wires get coated with varnish or something. Using steel wool (very fine 000) gently polish the wires to remove any deposits on them. They are delicate so be careful. The shorting bars which are gold plated now make good contact and the problem should be solved.

Hope it works for you.

Hi Dave,

I've cleaned the fuel sending units several times and in one case replaced the entire unit with a new one. Problem still persists. That's why I contacted VDO. I sincerely think the gauges have an inherent fault. Especially since the upper range of the fuel gauge reads fine, it's only the lower half that starts dancing...weird.

Many times on early cars the wiring at the tank sensor crack & you can get that dancing.
Just remember that this is only a variable resistor & over time they ALL will wear out.
The newer cars ie; 1995 & later DID have a design problem and they say it is due to the LOW EMISSION gasoline that is used here in the US.

The problems I have had occur on Diesels, not gas cars, and makes the last half of the gauge meaningless. The reserve warning light works ok, but the jumping guage is a pain in an otherwise very sound machine. Jim

According to another poster, please don't use even fine steel-wool or emergy cloth to clean connectors.

Microscopic bits of steel-wool get embedded and corrode. Confirmed by a microscopic visual inspection. Erasers are also a no-no for an electrical cleaner as well.

He suggsted using a 3M "red" Scotch-brite which leaves no particulates, followed by a dose of the proper DeOxit for either "tin" or "gold" plated connectors.

Good luck,
:-) neil
1988 360TE AMG
1993 500E

My '87 300TD is starting to do the same thing. The gauge works well until about a 1/2 full. Then the needle on the gauge flips back and forth from empty to the "actual" level. Will check sending unit first.

The gauge on my 'gas' car does the same. Only when below half a tank, it sometimes dances. No other indicator does the same.

You'd think that if it was deposits on the wires of the sending unit, it would affect the entire gauge and not just the lower half? Granted, there is usually more gas in the lower half for longer periods that the upper half, but still?

So, is it the gauge that is faulty or the sending units?

This is definitely a common problem that doesn't seem to have a simple solution...

The W202 has two fuel tanks (hence two senders). It sounds like your problem occurs at the point when feed switches from one to the other (I am told this is how it works, rather than drawing from both simultaneously). Unfortunately the tanks have to be dropped on the W202 to replace the senders. I've just had mine done today under warranty (guage showed empty when tank was very full, probably a sticky float).