My 1983 240D, when warmed up only gets to the bar above the 40C. I'm assuming that is 60C. I have read in other postings here that the thermostat doesn't open until 160F. I still get heat even at just above the 40C mark. The only time I can get this car above that second mark is when driving on the highway, then it settles in around the 80C mark which is roughly 175F. Does this mean my thermostat is stuck open.

Help, Paul

Stuck open or no thermostat at all.

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Never a dull moment at Berry Hill Farm.

First off, the temp sender/guage (as a working system) can be off kilter and you really don't know what the accurate temp is until you put a digital laser thermometer on the sending unit. If you have a relationship with a mechanic most will have one of these and it takes all of 1 minute to diagnois the accuracy of the readings.

Once you determine the accuracy of the system, then proceed. You probably have a bad or "tinkered with" thermostat. My experience is that the Whaler brand from Autozone has a larger opening at "full open" than the dealer or Behr brand. The frame construction is different. I have checked them on the stove.

Check your thermostat in the kitchen on a pot of boiling water with a meat thermo before installing.

I currently a thermo that opens too soon, the engine takes too long to heat up and I need to replace. Only had the car 2 months. Yes I checked the temp system and its reading accurately.

My previous 300D temp reading system was off by 17 degrees C. As long as you know where you start, then you can properly diagnois.

BTW there is an approx. 10 to 15 degree C temp difference between the 80 degree thermostat and the temp at the sending unit (after the coolant has circulated through the head).

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

I have to assume that the thermostat is bad or non existent only because the car will deliver heat as soon as the gauge reaches the 40C mark. Keep in mind the heat is only barely warm. Another bit of info is that under city driving the heat really never gets hot.
I only have a 6 minute commute to work at 5:30 am and with the recent weather around these parts(0-20F) its a cold ride at that, even when I let the car warm up for 20 minutes.

Thanks, Paul

I am a guage freak...I love to watch my gauges as these are the eye into the engine, brakes, battery etc...

I just purchased an 83 (my previous posts say '82, my mistake) 240D. I noticed the temp guage ony got to 80C what I was on the freeway.

Because I am a guage freak, I went to the Merceded Stealership and paid $25.60 for an OEM thermostat. I installed, and flushed the coolant, 2 days ago. Now it is perfect! The guage heats up a tick ovver 80C and stays there during normal city driving. When under load or on the freeway, I get to ~90 tops!

The ambiant air temp is ~60F.

The extra money spent was well worth it!!!!

Anthony

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'83 240D (W123) 321K miles
250KM Mileage Award
500KM Mileage Award

'84 300TD (W123) 215k miles
250K mileage award pending