Somehow my 84's glowlight knew how hot the engine was. Unfortunately all I got now is an 83 so I can't examine the glow relay or anything. Wonder how many pins the connector had...

the second sensor might be EGR related. I def. have two on my block.

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg

Ok so i parked the car on my driveway (already inclined) and on ramps (even more inclined) to fill the coolant system from the front of the motor. I used the top radiator hose, filled it up, put it back on, then ran it and burped any remaining air out of the system (squeezing top radiator hose till all the air finished coming out of the expansion tank). Unfortunately it made no difference in the running temperature, so at this point i'm thinking that the sensor or gauge is the culprit. Only way to find out is to use an IR thermometer i guess, so that is my next step.

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1985 300SD "Battleship"

Ok, i was checking some things on the car yesterday and found something that was indirectly related i think. Two or three years ago i had the alternator bench tested and rebuilt at a local automotive electrical shop, and sometime around then is when i started noticing higher running temperatures. Well yesterday i checked the voltage across a new battery i bought recently, both with the engine off and running. With the engine off i got 12.9V, which is very reasonable. Then i checked with the engine running and got a reading of 14.1V. Most of the german cars i've had, along with what i've read on some of the old threads here, lead me to believe that it should run right around 13.5V. Now being that the temperature gauge is nothing more than a voltage meter (or so i've read here), is it possible that the higher running voltage is the cause of my higher temperature readings on my gauge?

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1985 300SD "Battleship"

Man, things are kind of quite around here.......

Well this morning i tried to see if my theory would hold any water, where if the car while running was at 14+V but not running and only powered by the battery would be at 12.9-13V. Therefore if i run the car and it's reading it's normal (high) temperature but then shut it off and read the temperature with only the battery power, the gauge reading should drop. So after driving the car to work, i turned it off and waited about 5 sec then turned the ignition back to on but without starting the engine to see a before and after difference in the temperature gauge reading. The gauge was reading about 98C right before i shut the car off, then when i turned the ignition back on it was reading 88-90C. I'm thinking i may have discovered the problem, so i'm going to order a voltage regulator and see if that doesn't fix it.

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1985 300SD "Battleship"

I dunno... wouldn't that mean that the temp will move when you turn on the headlights or whatever?

My engine ran hot all the time. I found that the ground strap from engine to frame was loose. The temp sensor needs ground to work properly. Tightening and cleaning the ground strap worked for me.

Where is the ground strap?

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1985 300SD "Battleship"

Underneath, from one of the bellhousing bolts to the chassis. I think it's on the driver's side.