Sometimes I start the car for the first time of the day, and the radiator fan comes on. Why does it do that, if the engine is at room temperature, 65 degrees?

Most times it does not turn on, but other times it does.

1991 300d, 207k

Is your AC switched on?

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CENSORED due to not family friendly words

mine (electric)does this too, but @ every start-up over 65* F ambient temp.

new fan/clutch & belt, pbu set to econ

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1991 300D

No a/c or heat is on. Turned off.

Are you referring to the electric fan in front of the condenser or the belt driven fan on the water pump?

Electric fan operates off coolant high temperature or high a/c system pressure.

Mechanical fan has a viscous clutch that normally engages on high air temperature but on startup the fan will typically operate briefly (due to the oil pooling in the unit at rest?).

Does it roar like a garbage truck? If so that is normal and means you have a properly functioning fan clutch.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

I hadn't looked at which fan but will try to check tomorrow. I'm just guessing it is the one in front of the condenser because it's pretty loud. Even if it's working as a properly functioning fan clutch as you say, it's intermittent. Sometimes it will be on at a cold startup, sometimes it won't.

On 1987 124s the electric fan is directly controlled by the pressure and temperature switches via the relays.

Post 1987 they changed the fan control so that the climate control managed the fan. Maybe as part of the power on routine it spins up the fan...

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Come see us for help!

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check out Servicing Stop as they fix anything and everything to do with cars and have a brilliant service, they pick your car up, fix it and drop it back off! Plus 50% off your service!

I had this same issue in my 95, it was solved after changing the push button unit for the AC/heater system in the dashboard - some loose solders cause this.

The high speed function of the fans are controlled by the unit as a trigger to a relay in the fuse box. The push button unit refers the coolant sensor on the front part of the head for this function. To test a normal system one just disconnects the sensor and the fans start on high.

The older cars 86-87 etc had a switch in place of the sensor directly controlling the high speed relay.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Thanks.
jeff