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Uhm mine is euro spec, I forgot to mention that. EDIT: It's manual gearbox

The manual trans gets an electric fan, the automatic trans gets the belt driven fan with the viscous couple (fan clutch). The electric fan and the belt driven fan both do the same thing, although they do it differently. They pull air through the radiator at low speeds so that the radiator can shed the heat due to the airflow. When the car is going fast enough to physically force air through the radiator, the fan (electric or belt driven) have no effect -- the electric fan likely does not turn on, and the belt driven fan freewheels.

Someone talked about the Aux Fan, that comes with the AC system. There is an electric fan in front of the radiator (and heat exchanger) that is part of the air conditioner system. It provides additional airflow when the AC is turned on.
 

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'03 325iT Mystic Blau
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The manual trans gets an electric fan, the automatic trans gets the belt driven fan with the viscous couple (fan clutch). The electric fan and the belt driven fan both do the same thing, although they do it differently. They pull air through the radiator at low speeds so that the radiator can shed the heat due to the airflow. When the car is going fast enough to physically force air through the radiator, the fan (electric or belt driven) have no effect -- the electric fan likely does not turn on, and the belt driven fan freewheels.

Someone talked about the Aux Fan, that comes with the AC system. There is an electric fan in front of the radiator (and heat exchanger) that is part of the air conditioner system. It provides additional airflow when the AC is turned on.
That isn't strictly true. A/C state is one parameter that goes into determining auxiliary fan operation but that's not all that the DME uses to determine it. This is evident when you consider that when you do the electric fan conversion you're using the same feed to run the puller fan as was used to run the auxiliary fan and you're not doing any coding at all to change what triggers it.
It's an oversimplification to think of the aux fan as just an A/C fan.
 

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For Clarity and future search my 2000 323i Automatic with a M52TU engine and a production date of 11/99 has a fan clutch and a pusher electric fan.
 
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