M103 Temp Gauge Failure: Which Sensor?

[350SL4spd]

Hey All,

On the highway the other the day the engine temp gauge on my '91 300E started bouncing between engine temp (under 80*C) and the bottom peg (0*). It would intermittently read temp and then bounce around & fail.

My question: Which sensor feeds the gauge, where is it located, and how can I test it?

I see three sensors/sending units listed on Fastlane: eng. temp. sensor, water temp sensor, and water temp sender, but I'm not sure which feeds the dash gauge.

I'm sure it's easier to check the resistance of the sending unit under the hood before I try to rip the Instrument Cluster out & look for loose wires/bad gauge...

[Arthur Dalton]

Single wire sensor

Here are the specs for the sensor with the gauge reading at each value

OHM 110 = 60C
67 = 80C
38 = 100C

I suspect you have a poor connection at the sesnor.

[350SL4spd]

Where is the sensor located? Is it the one on the driver's side of the head towards the firewall?

[brandob9]

Originally Posted by 350SL4spd

Where is the sensor located? Is it the one on the driver's side of the head towards the firewall?

Yes, it is on top, single pole, between cyl. 4 and 5.

[350SL4spd]

Thanks brandob9. Love your signature .

I'll post results when I know them.

[brandob9]

Try this one:

[Xsbank]

You should have got a wagon if you wanted more seats.

[Hit Man X]

Probably a connection issue, my SEL had this. I just tightened up the metal clip and away I went.

[350SL4spd]

Just an Update:

I finally got under the hood yesterday. I wiggled the single pole connector in the head and the wire fell right out of it.

Now I just have to get a 50' extension cord to get my soldering gun under the hood...