Help with low coolant temp please
 

1985 300D.
I am having an issue with either coolant temp or coolant temp readings and hope someone can help. Our temp gauge started reading low around 40c to 60c. It had always read around 80c before then. I assumed the thermostat.

I replaced it, and am still having the same issue. I tested the old thermostat, and it opens in some hot water no problem, so I have to assume there is another issue. (unless both thermostats are weak?) As I'm fairly certain there is no air bubble, and the aux pump seems to work (heat and defrost work at idle). The coolant temp sensor is my next suspect, unless there are some other options you all may advise. After some research that seems the likeliest culprit though. What say you guys? Anything else that can cause this condition? Thanks!

i'd check sending unit

Sinner,

Do you mean the temp sensor mounted in the head? That is the part I'm referring to. How does one check that? Resistance? What should the readings be? At what temps?

Thanks

well they do wear out,it would be a cheap fix,or borrow a infared thermometer

Coolant temp sensor installed. Issue resolved. Thanks.

For future reference, Diesel Discussion is the more correct forum to post this in -- it's right below Tech Help on the list. ;)