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Guest Anonymous

electric fan quandry

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Guest Anonymous

Yes I have had an electric fan for a long time it is controlled by a thermal switch on the coolant return manifold and is set to turn on the fan at 190f. System works just the way it is intended to work except: when I am in stop and go traffic and the fan goes on at 190f. The traffic clears and my speed picks up and I expect the temperature to return to 175f my thermostat temperature set point. It does not cool down until I am pounding along at 60-70mph when it finally drops and the temperature switch turn off the fan.

What is going on? Well when the fan turns on it rotates at a certain RPM that is good enough to cool things to about 195 on a hot day. When I finally start to move and expect to get 30 to 40mph air through the radiator the fan will not rotate faster than the set operating speed and dramatically reduces the flow that normally just free rotates the fan blades when it is off. That fan will only rote at a set speed and will resist going any faster. To get enough flow to finally cool the engine properly I have to go fast enough 60-70mph to overcome the operating electric fan that is restricting the flow.

I just put a manual fan shut-off switch in series with the thermal switch so I can kill the fan whenever I want to and return it to a free rotation state to allow air to flow normally.

Still having fun

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is the fan blowing air INTO the engine bay and not pulling air from the engine bay outwards?

This might be a wild guess, but this sounds to me like at low speeds the radiator is still being sufficiently cooled, but when you start moving the fan blowing against the direction of the wind entering the engine bay is creating a stagnant air zone that is only overcome once high speeds are reached.

I can't think of a reason otherwise. Check that first, and if it is blowing in the right direction than the next thing I would try is hooking up a manual over-ride for the fan and giving temperature readings when cruising.

Is the radiator core clean? is there anything blocking the free travel of air?

EDIT: realized you already have a manual over-ride. What fan do you have in there? Most vehicle electric fans don't resist being spun faster than their "powered" state.

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is the fan blowing air INTO the engine bay and not pulling air from the engine bay outwards?

Agreed had problems with a Ford and a fan running backwards. Will cool perfect on traffic jams and overheat when running.

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Any progress in this? I'm curious about what the issue is...

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my thoughts are to

remove the electric fan, the bundle of wires, switches,

relays, brackets and toss all of it over the back yard fence

install a recored Original BMW 2002 radiator,

a new BMW water pump, a NEW BMW thermostat,

a NEW BMW "Tropic" red fan blade, adjust the ignition

timing with a TIMING LIGHT and you'll be golden.

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