Fan clutch engaging at too low a temp?

[benzfan]

I have searched and searched, but not found anything like this. The car is a 97 c36. it comes up to normal operating temperature, and using the gauge and climate control head unit, stabilizes around 82-84 deg. Normal. But then, the fan clutch engages, and as I drive, the engine temp. drops to 70deg or so and stays there until I am in stop and go traffic again whereupon it warms up again. The fan clutch engages and I get the associated air movement noise (loud). I wouldn't have thought with such an engine temp. and an ambient temp of only +2C, that the fan clutch would engage at all. Any experience/thoughts?

[400E]

I don't have any experience with that model, but to me sounds like either a thermostat problem or a problem somewhere in the temperature sensing circuit (e.g. a bad sending unit).

I have deliberately modified my mechanical fan clutch to stay engaged at all temperatures, and it doesn't affect warm-up -- the thermostat, if working properly, prevents cold coolant from going to the radiator so it shouldn't matter how much air movement you've got...

[jbaj007]

Doesn't sound like the fan clutch is right, but, for sure, there is a thermostat problem if it goes down to 70ºC after warm-up. The thermo on that car is an 87ºC; shouldn't go below that after warm-up.

I'd also shoot it with an IR temp gun at the head, therm housing and radiator to make sure the numbers are being reported correctly by the gauge.

[benzfan]

Thanks,
I'm planning to try the thermometer, but my thought is this: There is slight evidence that the rad has been replaced, along with the repaint of the support on top. There is no evidence of body work anywhere else on the car, nor any record of insurance claim. I think that someone slapped the rad backwards in a minor way, but bent the bimetal strip on the fan clutch in the process of the rad striking it, effectively accomplishing the same thaing as a longer pin, i.e. lower engagement temperature. The thermometer will tell me. Even if it is a bad sensor, the temperature shouldn't wander. It is winter, so the cooling effect of the clutch fan is quite dramatic. I have never seen it even engage on my c280, no matter what the weather and load, and I know it works fine, that's why this one surprises me.

[jbaj007]

I thought it was a SHORTER pin that gave engagement at a lower temperature.....at least that what I figured from the diagram of the reservoir system of the fan clutch. When I refilled mine with the 10,000 CST silicone, I shortened the pin to make the "tropical option" out of it. I could be wrong (heaven knows it happens often), but I was pretty careful when I did the mod.

Of course it does matter which side is "up" on the bi-metal strip, but I thought it only went in the slots one way. Maybe I put it in wrong, but again, I was careful (honest ).

I still think the thermostat is glitchy, also.

[benzfan]

Hmm,
I finally found a drawing that indicates this may be so...
So much for my theory. I wonder if someone has already modified my fan. I still need to check the temperatures accurately, but it should not be engaging at these low ambient temperatures.

[benzfan]

After checking with an infrared thermometer and obtaining indications of 62C on the head, I had the fan clutch and thermostat changed. The fan clutch was indeed engaging at too low a temperature (58C or so) although I can't imagine what type of internal failure would cause that. The thermostat was not doing its job either. The engine now runs rock steady at 83C.