Re: E34 525i HIgh Speed Aux Fan not running

[alex.fadeev@xxxxxxxxxxx]

"Eugene Hoe" <eugene@domain.elided> wrote:
> My E34 525i M20 has the problem of getting very hot when the car is
> stuck in a traffic jam or stationary on a hot day.

Eugene,
How hot is 'very hot'?

> Found out that
> the aux fan is running only on Low Speed, the High Speed isn't running
> when the temperature goes up. I checked the fan itself and did a bypass
> to make sure the high speed is working and its working fine. So next
> I checked the sensor attached to the radiator which basically triggers
> the High Speed fan when the temperature reaches a certain level, that's
> fine too. But yet the high speed fan doesn't activate when the
> temperature goes up.

Eugene,
In most normal (street) situations the auxiliary fan will never run at high
speed.
On M20 engines the aux. fan runs at low speed whenever AC is on or when the
coolant temperatures exceed 80C. 95% of the time it's the former. The aux.
fan will run at high speed if and when coolant temps exceed 100C, but now
we are talking about a major overheating situation.
Pretty much the only chance to see aux. fan run at max speed is during
testing or if your viscous clutch fan is toast and your are stuck in
traffic revving the engine to red line. Just idling in traffic is unlikely
to require aux. fan speeds above slow.

> Anyone got any idea what could be causing this?.
> I know I can bypass and enable the high speed fan to run permanently
> but that would only shorten the life of the fan. Any ideas would be
> appreciated. Tks.

I think your aux. fan works as designed.
If your car is overheating, look into the viscous clutch fan. Test it by
trying to stop the fan from spinning on a fully warmed up engine with a
rolled up newspaper. If the fan stops, your $60 clutch is toast and need to
be replaced.
If the fan clutch is OK, than suspect internal cooling system issues
(blocked radiator, sticking thermostat, dying water pump, etc).
Do not force the aux. fan to run at full speed all the time. It may sound
like a brilliant idea until you look up the aux. fan $300+ replacement cost
for parts alone.

alex f

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