BMW E28 cooling and viscous fan
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Why does the E28 overheat at idle or at motorway speed?
The most common cause is a faulty viscous fan (a fan that engages according to temperature) that does not engage. Cooling then relies entirely on the radiator. Also check the thermostat: if it does not open, replacing the viscous fan will not help.
How do I check the condition of the viscous fan?
When cold, the fan spins freely. When hot, you should not be able to stop it by hand. If it does not engage, replace it. Store the viscous fan upright, because if left lying flat it can lose its function.
What should I note when replacing the viscous fan?
The viscous fan has left-hand threads, so the nut is loosened and tightened in the opposite direction to normal. Check the thermostat's operation at the same time.
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