OK, I'll weigh in on this thread. Since the temps have summered in Tennessee, I have seen my new to me 1987 300D get pretty warm.

Driving down the interstate with the ambient temp at 95F, when hot soaked, my indicated temp is about 95-98C. With a steep grade, it will range to about 105C and return to 95-98C on the flat pretty quickly.

If I get off of the interstate and shut the car off. When re-started it will indicate about 115C for a very short time and immediately begin to moderate as the car moves, even at low speeds.

I have replaced the thermostat with no change in behavior. I have determined (at least to my own satisfaction) that my Visco fan clutch is a non-performing asset. It does not change speed with the engine, regardless of indicated temp and has absolutely no drag on it at idle, again, regardless of the temp.

I have purchased a used Visco fan clutch from PGAuto and will install it sometime this week. I will report my experience here.

One thing that I do find interesting, is that the car does manage to keep itself below about 115C. I can only surmise that the auxillary fan is responsible for this. If I let the car idle from a cold state in the driveway, the aux fan will begin to come on well below 100C. I guess, as the demand for AC lessens due to the interior of the car getting near the required temp set by the climate control, the "coincidental" aux fan help goes away. This is how I explain the fact that the car will go to 115C when coming to a stop after a long hot soak. The aux fan must be coming on because of temp at some point, which is keeping the temp from running away.

Ambient temp seems to make a huge difference. At 80F ambient, the car rarely goes over 90C, and then for very short times.

If I see the temp going up (which I watch closer than the speedometer these days) I can bring it down quicky by punching the defrost button and spinning the wheel to max. This can be uncomfortable for a time.

As I said, the fan clutch is next and I'll let you know. Comments and suggestions are welcome...

BR,

Steve (8C>