Once in a while, my temp gauge, when car is warm, hops around around and drops from 100 to around 80 then stabilizes and goes back to the 95-100 degree range. Anyone else ever have this happen? I've only noticed it recently. Electrical? Sensor?

Sounds like either a faulty temperature sensor or a bad ground/wiring on the instrument cluster for the temperature gauge.

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1989 300CE

My guess is a bad ground. Are other gauges/clock affected?

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1989 300E

2005 Acura TL

2011 Hyundai Elantra Limited

Swing hard! Take chances!

Everything else is fine. I was thinking maybe a bad temp sensor. Wiggled all of the wires and still had same problem but just very temporary. I'll keep an eye on it. Is this the temp sensor near the firewall or the in the middle of the valve cover under the air housing? Thank you!

Bad ground up to the cluster panel, very common problem.

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600SEL '91
300E 4Matic '88
240D '83
280SE '77
350SE '73
The most complex systems can fail in the simplest way.
Contra verbosus noli contendere verbis, sermo datur cunctis, animi sapientia paucis.

i don't believe in the lord! He's never bought me a Mercedes Benz.

We had the same issue with the fuel level gauge on a 1992 300E a few years ago. It would - only below half a tank - flicker between empty and half full intermittently and the dash illumination on the left didn't work either. The common reason was a faulty rheostat, although the car moved on before we had it checked.

I wonder if a dying voltage regulator could cause those same symptoms?

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

Yes. It could be something like the voltage regulator although mine is new. I can reach in there an reseat it. Hasn't happened again since my last reply. Where is , what is, the rheostat?

What is the fix for the bad ground?

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1984 300 SD 384,000 Miles

Happened again coming home. I noticed it happens when it is around 55 degrees outside. Warm outside, doesn't do it. Hmmm...