I got a lot of good suggestions from my last post (1-16-00), but I still have the high temp problem. Up until 3 weeks ago, the temp in my 85 300D (202,650) never rose above 95* (in Summer with A/C on). Now it is running 85*-90* with heat on and up to 100* with heat off.

This is what I've done in the past week>>>

1. Replaced thermostat with 80* MB OEM unit (installed with arrow up!)
2. Replaced Expansion tank cap.
3. Flushed system 3 times
4. Replaced Radiator today with brand new radiator (not a rebuild).

I also replaced the expansion tank and water pump about 9 months ago.

Even with the new radiator, the car is still running a good 10*C hotter than it did only three weeks ago. I feel I just wasted $ on a new radiator as I am seeing no temp improvement over the old radiator.

While flushing the system, I did so with the thermostat out. After 35 minutes, the temp never got above 50*C and the defrost was barely blowing warm.

Questions:

1. Could it be a bad thermostat (even though I just replaced it)
2. Could it be a bad waterpump that is not showing visible or audible signs of wear. (I never have felt a surge when squeezing the upper hose at operating temp)
3. Could it be a bad temp sensor? (how do I troubleshoot?)
4. Is it gremlins?

Thanks so much for replying with suggestions.

As you have found, this is a hard one. You could have a bad gauge and or sender. You easily could have a faulty new thermostat. New doesn't mean good. There is an arrow on the thermostat that has to be clocked a certain direction. The other thing is that more than one degree of thermostat is available for your engine. Are you sure that you have the correct one.?

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Does your car have a thermally activated cooling fan? It could be slipping or sleeping.

And yes, audit your temp gauge and sender.

Did you replace the cooling system components simultaneously, or one at a time?