my water temp reads low for the first half hour or more, then gradually makes it to 40 c, what the... is my sensor bad? I am running sinthetic oil in it and it is supposed to run a bit cooler than normal but sheesh 40 c... it eventually gets up to 60 c if I am going 60 mph climbing a hill but then back down to 40 c when I am going 35. Any ideas?

Thanks

Tahoelobo...

To test if your sensor is bad, get yourself a $10 infrared thermometer. When you've driven that 30 minutes, pull over, pop the hood and shoot the thermometer at the side of the cylinder head by the glow plugs and such. See if it's really reading 40C. If not, and you're seeing more like 80-90C, everything else is fine and the reading is bad - perhaps due to the sensor, gauge, cluster grounding, etc.

If you find the reading is correct and your engine is really that cool then your thermostat is stuck wide open and needs to be replaced.

__________________
1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

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Do you have heat? If it's only getting up to 40-60C, your heater will be pathetically lukewarm. If this is the case, replace the engine thermostat -- it's a half-hour job.

Of course there are other potentially unrelated things that could cause poor heating. Testing with an infrared thermometer is the most sure fire way to know. It's cheap and easy and the thermometer will come in handy now and again.

__________________
1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!

thanks folks, I did the thermostat a year ago or so, and I do have heat so I will try to measure the engine temp when it is warm and see if the sensor is bad. Is there a way to test with ohm-volt meter?