I am a newbie, so please forgive me for asking what may appear to have been answered many times. I replaced the water pump, thermostat and belt on my 1988 300CE. I did this because the temperature gauge had begun to "creep" higher than what was normal for this car. When I restarted the engine, the temperature again began to climb above the normal range for this car. After replacing the above listed components did I notice that the auxilary fan was not turning on! It is possible that this was the original villian of the rising engine temp. I have replaced the relay, checked and replaced fuses (none had failed) and have replaced the resistor on the left frame rail. I can make the fan run at low speed with the key in the on/run position by ground the brown/blue wire at the Receiver Dryer and at high speed by disconnenting the 2 pole switch at the top of the head. What am I missing

The high fan will not come On until 105/107C. You have verifed fan circuits.

Does it only run hot w/ac on???

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A Dalton

Low speed on fan is for AC operation. High speed is for when engine gets pretty hot.

Your problem sounds like possible clogged radiator.
Remove it and have it serviced by a radiator repair shop.

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1990 300CE. Garage kept all its life. Looks & Runs Like New. Everything works. White w/Palomino int. Pioneer 12 CD player in the boot. 17" Enkei LX-F Chrome wheels w/Falken Azenis ST-115 225-45 tires. Tinted windows. Black sports grill w/Euro clear front lamps.