I have had the instrument cluster out and have fixed the clock and the speedometer (tedious!) and now I want to tackle the temp gauge. The temp doesn't hardly move (if at all) and I know to check the thermostat (but since I have some heat I suspect the car is heating up some).

I have read thru most of the posts on this topic but I'm still confused. The fuel gauge works as does the oil pressure gauge so I'm thinking that it's probably not an electrical problem in the cluster. Would that be right?

I checked the resistance of the sensor (on the left side between 2 and 3 GP) and it read over 1000 ohms. I'm not sure I checked it right though - I grounded one lead and touched the other to the temp sensor post (it only has one). I did this with engine cold (ambient temp probably in the 50's) and I'm pretty sure 1000 ohms is way too high, but I'm not sure - should the engine be warm/hot?

Any troubleshooting suggestions? I was wanting to check this out since I have the instrument cluster out.

Thansk, ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

With the key in the on position, ground the wire going to the temp sensor. Have someone in the car when doing this to tell you what they see on the gauge. Do this quickly because I don't know if there's a resistor in the circuit & 12 volts may be too much for the gauge for too long. The gauge should peg out. If it does, the problem probably lies in the sensor or a bad connection to it. 1000 ohms seems high when cold. The ohms should drop as coolant temperature goes up. Paul.

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'84 300CD 290,000

FWIW, I just checked mine (82 300D) with the engine up to temperature (80C) and measured about 70 ohms across the sensor. I haven't measure mine cold.

I just checked the gauge per Paul's instruction and the needle pegged when I grounded the wire that connects to the sensor. I'm thinking it's the sensor that is bad, so I am going to replace that and see what happens.

Thanks for the help.

ryan

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE