I know everyone is probably tired of my ?s about my car but please bear with me. I hope this is the last ?s I have about this subject. My 82 240d's temp gauge has been showing it running hot so I've done everything I know of except changed the waterpump. After posting a ? about changing the pump I felt it might not hurt to take some temp readings. I used a IR temp gauge which I know isn't probably the best method but it's what I have. So at idle my cars gauge will go all the way to 120c. This is after the car has sat running for about 10 to 15 min and stays there. I shot the top radiator tank by where the inlet hose attaches and got readings between high 70 to mid 80c. Then shot the bottom tank and by the supply hose and got readings between mid to upper 40c. I also took a reading where the temp sending unit is on the block (in between the glow plugs, I hope that was it). I got a reading of between 80 to low 90c there. I also took readings where the top hose hooks up to the engine block and got pretty much the same reading at the top of the radiator. My ? Is does it sound like my temp gauge is off and do you think it's safe to drive somewhere close to home (1/4 mile or less) to have someone verify my readings?

Thanks,
Mark

There is probably a poor connection due to corrosion at the temperature sensor on the engine.

Unplug the wire from the sensor, clean the female pin of the wire and the male pin of the sensor with some electrical contact cleaner.

That should clean up your temperature signal.

I had a loose female pin on my 78 W116 300SD sensor wire which gave me erratic temperature readings.
Crimping the pin slightly re-established a good electrical connection.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Where does your temp gauge needle rest? Mine always read low, when I pulled the cluster I realized that the needle was not really centered. It could sweep much lower on the gauge than it could max out. I am not sure how to calibrate the gauges properly, but i set mine so it could sweep about the same amount in both directions. Had a similar issue with the fuel gauge.
The FSM may have resistance readings for the temp sender too. I am not sure

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'85 300D - federal spec, built in late 84. 85 300D Complete AC System Rebuild

When it is cold before start up the needle sits where it should, at the bottom of the gauge. I will check the connection at the temp sender tomorrow after work. Keeping my fingers crossed thats it. Ran it today with the radiator cap off and after the t stat opened it looked as though antifreeze ws flowing across the radiator. Makes me thing the pump is working..