On a really hot day here in the south I can hear my viscous fan clutch locked up and turning the engine fan but only for a minute or two. That fan moves a lot of air and given the temps you saw, your engine fan should have been noticeable by ear. If you don't remember hearing the "roar" from the mechanical fan when she was hot I think a simple test would be to roll up a newspaper and try to stop the mechanical fan. It should be locked in at temps above your center point on your gauge (115C) and you should not be able to stop the fan.

From the Bimmerforums:

1. Start the car (cold) with the hood open and note if the fan is turning, increase the engine RPM and note if the fan turns faster and the noise increases, if it does, first good indication, if it does not increase speed/noise, clutch is bad and needs to be replaced. (Remember, this must be tested after the car has been off for and extended period, over night etc.)
2. Leave engine running and note if the fan starts to slow down after 2-5 minutes, speed/noise should diminish and even raising the RPM, the fan should not make as much noise as when first starting, if it does slow, this is the second good indication. If speed/noise does not decrease, clutch may be “frozen” and should be replaced.
3. Leave the engine idle and watch the temperature indicator. When normal operating temperature has been reached, some increase in fan speed/noise should be noted, in particular when the RPM is increased. If temperature is fairly stable and the fan noise/speed increases or cycles, third good indication. If temperature indication continues to increase, with no increase in fan noise/speed, clutch is defective and should be replaced.
4. After the engine is at normal operating temperature or above, is the only time that the “rolled up newspaper” test that many people talk about should be performed! Take some newspaper and roll it up into a long narrow tube. Be carefull, keep hands and fingers away from the fan while performing this test! With the engine at full operating temperature and idling, take the rolled up paper and insert it on the back side of the fan and try to reach the hub of the fan avoiding the blades until close to the hub. Push the rolled paper at the fan increasing the friction to the hub area of the fan. If the fan can not be stopped easily this is the fourth good indication, if it can be stopped the clutch is defective and should be replaced. Again, this test can only be performed when the engine is at or above full operating temperature.
Testing can be performed in any order but just make sure the conditions during testing are those that are specified for that specific test.
Do not continue to operate the engine if the temperature continues to rise and certainly stop if the temperature approaches “redline”.

Yes, my sons z-3 would heat up in traffic, viscous fan clutch had very little “bite.”


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I am getting confused, viscous fan, engine fan and electric fan? I am talking about the giant fan directly in front of the radiator, the one I have to take the blades off and remove the housing to work on things. I think this is the viscous fan/clutch.

My current guess, is that this is going. Rationale is its blowing weak, so if it blows weak cool air, things are stable, if its blowing weak hot air, then the coolant starts to overheat. Or the t-stat is restricting flow and again the warm air is just not sufficient with the weaker.

I'' get to work and report back with the solution.

The viscous fan clutch is the center part of the spinning fan with blades. As the temp increases the fan spins at a higher rate as the viscous materials tightens the hub. When you first start the car cold the fan sort of lopes along, once the temp rises the clutch “ bites” more and the fan spins higher pulling more air over the radiator and increasing the cooling effect.

These thing fail so that if it doesn’t tighten enough the fan doesn’t spin fast enough. Usually in bumper to bumper traffic. But, never seen one fail to the extent you would get a quick over heat.

To test carefully stick a bit of rolled up newspaper in the fan after its at op temp. Ease it in. If the newspaper causes the fan to stop or even slow significantly the clutch is bad.

Safer way is with the engine hot but off try to spin the fan by hand. If the fan spins then the clutch is bad. If it resists, not your problem.


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Yes, confusion for sure. On the 3.0L M54 engine the fan in front of the radiator is the electric fan used mostly for A/C operation. Behind the radiator attached to the engine is the viscous fan. If you didn't hear a jet engine when your X was overheating, your viscous fan clutch is bad. Believe me, you can hear it when it is functioning. That fan moves A LOT of air when the clutch is engaged.

Indeed loud and windy if you open the hood.


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Loud and windy sitting in the driver's seat with the windows up and A/C on full song. But then I listen to every little sound my ole girl makes... ;)

I'm about to replace my viscous fan clutch - it works correctly but the bearings have shat the bed... :-(

https://youtu.be/kdhRraCZorA

Got a Hella Behr (OEM) unit for a decent price in the UK.

done, ordered a new fan clutch... if that doesn't eliminate my issue as we head into summer, I will change out the thermostat again, not a big deal. I like that I can work on this car, makes it kind of fun for someone who is inclined. I really need to get in ad do my valve cover gasket and the intake boot. thank all. I will report back.

Intake boot is way harder than it looks. Mainly due to the Metal clamps being hard to get a tool on.


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