For months, my temperature gauge was jumping up and down like crazy once the car heated up, and now the darn thing finally just died. I've checked the wires, replaced the Temperature sensor replaced the thermostat and since it died, changed it with a used one and it still doesn't register. Now I'm lost.

Is there a specific relay that controls the temp. gauge only? Any help would be appreciated.

AARON ROCHARD

1976 230 W115

I have been having similar problems with an 83 240D. I replaced the sensor and installed different, but used gauges. I am willing to go with new ones, but I am not confident that it will work any better, so I am still plugging away. My daughters have the car now while I am fixing the 80 300SD. When I get it back, I thought that I would track the circuit board to make sure nothing was a-miss. The ground does go through the glow plug relay, but that is true for all of the instrument cluster and everything else seems to be working. I am getting power to the sensor.

I am stumped on this one.

Let's see if we get any better advice on this one.

I think you are mistaken in the ground through the glow relay idea! According to my wiring diagram, the temperature sensor is screwed into the engine block, the ground for the engine is the heavy wire cable from the engine to the frame near the steering gear. The ground for the gauge (and most of the other instruments) is the main ground, located behind the instrument cluster. +12V is supplied through fuse 12 to the temperature sensor when the ignition switch is in the start or run position. Possible problems would be: 1. a broken wire from the temperature sensor to the instrument cluster - you can check that with an ohmmeter. 2. a broken or cracked trace on the instrument cluster board. (Most likely!) If you don't see anything, try resoldering all connections in the circuit path. This should be a fairly simple fix, I think.

Richard Wooldridge

That was my line of thinking too. I understand to trace the circuit board and look for breaks or cracks, but I am not understanding the connections. What are the connections on the circuit board, is it everywhere the something connects into the circuit and isn't that just about everywhere? I hope that this is not sounding obtuse, I really am not understanding.

I'm also afraid to remove the cluster, the oil pressure line is tough to get off as well as the speedo cable. How much would you say a mechanic would take to do this job ?

AARON ROCHARD

1976 230.4 W115

I had a similar problem on mine. The terminal inside the plastic cap on the temp sensor had corroded and eventually the wire just broke off. I found the temp sensor to be not screwed in very tightly. I believe it had been leaking a tiny amount of water around the threads for a long time, which eventually corroded the wire. I repaired the wire and terminal by careful soldering and replaced the sensor just for good measure using a small amount of liquid teflon type thread sealant. (I forget what it's called, PTF or PTL or something like that.) I tightened it as tightly as one dares tighten a brass threaded part (which isn't too tight.) No problem since repair about a year ago.

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Palangi

2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg



TRUMP .......... WHITEHOUSE
HILLARY .........JAILHOUSE
BERNIE .......... NUTHOUSE
0BAMA .......... OUTHOUSE

The wire to my sensor has power and looks good. Is there anything else it could be?

Hi Richard,

could you post the wiring diagram, thanks!

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1996 E320 since 1/16/08, 171K miles as of Feb 2011

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1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE

I am having basically the same problem, my gauge at times starts jumping all over the place from 100 to 60 and back then starts to climb over 120 which is when I get concerned and turn off the AC and put on the ehat to drop the temp. However when the gauge shows 120C I used my infrared heat gun and the hottest part on the cooling system I could find only registered 97C. I dont want to have a false sense of security with this car. I just got ot and its in awesome shape with absolutely no rust. Its a 1995 E300D.

Where is the temperature sensor? Is it where the wire goes to the coolant plastic tank? Has anyone installed another gauge instead? I was thinking of that because my oil pressure gauge also registers at the highest mark constantly.

Can these two gauge issues have the same problem?