I have always felt that the fan clutch has minimial effect at highway speeds. It would just propeller itself with the blast of highway speed air being rammed through the radiator. I once had the unfortunate experience to have the crank shaft pulley shear off my old 63 190D. No place to hook the fan belt. I ran the car and it actually ran cooler at freeway speeds without the belt on. ALways thought that was interesting. Of course it would overheat at low speeds. The fan clutch is affected by radiator temp via latent heat from the radiator. Exit temperatures from the engine are indicated on your temp gauge, so I assume the fan clutch should be engaged at high temp but low speed and not at high speed. For the clutch to engage at high speed, the air temp would have to be in excess of 105 deg C. Unlikely when you have air approach speeds in excess of 100mph. To test this theory, attach a basic thermometer between the fan and radiator, run the car at speed, come to a rapid stop, run out of the car and check the temp. Might work. I am almost to the point to do a detailed engineering evalaution of the cooling system on the 603 engines. If it was not for the variable speed aspect of the pump, it would be easy. One day in my free time. One thing I will check on my car is exhaust back pressure. This has not been mentioned as a source of an engine running hot, but it deffinantly is a source of additonal; heat being be added to the cooling system. Also engine timing. Anyway, watch out fopr those speeding tickets. Also, does your temp run constant or does it move around in normal driving.

henry


Henry

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63 190d (sold)
69 220D (sold)
69 280SL (sold)
76 BMW 2002 (sold)
86 190E-16v (Demised at Laguna Seca Turn 9)
87 300SDL (sold)
87 300SDL 135k
87 300TD 280k (sold)
95 E320W 311k
95 E320w 180k
05 C320 4matic
06 E320 CDI 90k (Totaled by a texting 19 year old girl in a nissan)
2013 GLK 250 Bluetek 4MATIC 295k