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Pelican Technical Article:

Fan Clutch Testing

Nick Czerula


1 hour1 hr






Infrared thermometer

Applicable Models:

BMW 323Ci Coupe/Conv (1999-00)
BMW 323i Sedan/Wagon (1999-00)
BMW 325Ci Coupe/Conv (2001-06)
BMW 325i/xi Sedan/Wagon (2001-06)
BMW 328Ci Coupe (1999-00)
BMW 328i Sedan (1999-00)
BMW 330Ci Coupe/Conv (2001-06)
BMW 330i/xi Sedan (2001-06)

Parts Required:

Fan clutch

Hot Tip:

Be careful when testing; keep clear of the fan when engine is running

Performance Gain:

Restore cooling system operation

Complementary Modification:

Replace older hoses

BMW E46 cooling system components include:

  • Radiator and coolant overflow tank.
  • Belt driven coolant pump bolted to the front of the engine block.
  • Electric cooling fan attached to rear of radiator. The cooling fan is controlled by the engine control module (ECM) via an output final stage.
  • Automatic transmission models: Belt driven fan attached to front of coolant pump. Viscous clutch controls fan speed based on engine temperature and rpms.
  • Electrically heated thermostat.
  • Automatic transmission cooler (heat exchanger).
  • Heater valve and heater core (for climate control).
  • Coolant level sensor inside expansion tank.
  • Coolant temperature sensor at cylinder head.
  • Radiator outlet temperature sensor
  • Coolant hose and lines.

A viscous fan clutch is as reliable as any other part of your cooling system, but it can still fail. The viscous fan clutch is mounted between the radiator and engine. The clutch controls radiator cooling fan speed and is dependent on engine temperature. The fan draws air through the radiator cooling fins, thus cooling the engine coolant. Depending on cooling needs, the fan clutch partially disengages the fan, located at the front of the water pump and driven by the engine drive belt. Disengaging the fan when not required saves power, since the engine does not have to fully drive the fan. However, if engine temperature rises above 90° C (194°F), the fan becomes fully engaged, drawing a higher volume of air through the radiator cooling fins. 

A common symptom of viscous fan clutch failure is engine overheating at idle or in traffic because the viscous fluid in the clutch has dried up or failed in some way. On the other hand, if a viscous fan clutch is stuck ON, it will rob your engine's power and decrease fuel economy. Another potential symptom of your fan clutch being stuck ON in a cold weather climate is that the heating system doesn't deliver sufficient hot air. The bearings in the fan clutch can also fail, causing a noise or fan blades to come in contact with the fan shroud.

In this tech article, I will go over how to test the fan clutch a few different ways.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches. 

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability. 

Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

This photo shows the fan clutch, installed on the cooling fan (green arrow).
Figure 1

This photo shows the fan clutch, installed on the cooling fan (green arrow). 

Clutch bearing free-play
Check bearing free-play by wiggling fan back and forth. Tilt play of bearing with diameter 120 mm is ± 0.65 mm If free-play is more than specified amount, replace with new. Spin test With engine cool and OFF, spin fan blades by hand. If the fan free-wheels without drag (the fan blades will revolve more than five turns when spun), replace the fan clutch.

Function test
Use extreme caution when the engine is running. Do not stand in line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Block the air flow through the radiator. Secure a sheet of plastic in front of the radiator (or air conditioner condenser). Use tape at the top to secure the plastic and be sure that the air flow is blocked. Be sure that A/C is turned OFF.

Start the engine and raise idle to 2400 RPM.
Figure 2

Start the engine and raise idle to 2400 RPM. Within ten minutes the air temperature should be up to 88°C (190°F). Fan clutch engagement should have started to occur between 88°to 90°C (190°to 194°F). Engagement is distinguishable by a definite increase in fan flow noise (roaring). Fan speed will increase. Use an infrared temperature gun to measure fan clutch temperature.

When the air temperature reaches 88°C (190°F), remove the plastic sheet. Fan clutch disengagement should start to occur at 60°to 79°C (140°). A definite decrease of fan flow noise (roaring) should be noticed. If not, replace the defective viscous fan clutch.

Comments and Suggestions:
JOHN Comments: Wow, you people still reply to these thread. Great customer service.

As for my problem, I don't have any real cooling issues right now, except for a very small leak at the thermostat to upper radiator hose fitting. It's either a bad coupling on the t-stat or a badly produced radiator hose. Replaced both, still leaking. It's a very small leak so I'm just watching it.

This is what brought me here, in watching my small leak, I haven't noticed my fan clutch turning on. The, "roaring" occurs at cold start, then goes away, testing with hood open and Rev to 2500 periodically. But, when it get hot, it fluctuates between 198 and 204°F and I can not hear any fan difference.

My question is, if the fan is not engaging, why is my temperature not continually rising. And, could the fan clutch still be bad even though my temp doesn't rise?
November 22, 2017
  Followup from the Pelican Staff: The fan will spin as needed when engine temp demands it. That is the point of the fluid in the clutch. What you are hearing is likely normal. - Nick at Pelican Parts  
lil tito Comments: i found a belt or ring under my hood that was tucked in by the sensors it almost looks like a house hold vacuum cleaner belt is there a belt or ring on my 1999 328i that is big in size like that ? also when i took the cap off where u enter the engine oil it looks a rusty briwn color what does that mean?
October 28, 2017
  Followup from the Pelican Staff: The brown color on the oil cap is normal.

The belt doe snot look familiar to me. Looks more like a large O-ring. - Nick at Pelican Parts
Liltito Comments: Hi i have a 99 bmw 328i an noticed a sensor was off im having overheating prob could that be why
October 24, 2017
  Followup from the Pelican Staff: What sensor is disconnected? if for the cooling fan, it is possible. - Nick at Pelican Parts  
Manny Comments: Hi, can anyone pls help with the size of the bolt for 325i reservoir mounting bracket fastener, both the top and bottom. I misplaced mine and need them replaced. Thanks
January 14, 2017
  Followup from the Pelican Staff:
I think they 6mm x1.0 Torx bolts.

Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
Todd Comments: I am baffled. I own a 2000 328i, I am experiencing cooling issues. I have replaced the thermostat, upper and lower radiator hoses, radiator cap, waterpump, coolant tank and bracket. System has been bled. Topping off the system cold and then running the vehicle I do not get heat. Running at in the garage the temp gauge does not go over the mid range. I drive it down the street a mile or 2 and the temp gauge starts climbing, leading to coolant overflowing out of the top of the coolant tank. Fan seems to be loud compared to my 2002 325ci. I have attached a photo of the block when the thermostat housing was removed. The corrosion presents a concern and leads me to believe a potential issue with the flow of coolant. Any input would be greatly appreciated.
September 1, 2016
  Followup from the Pelican Staff: I would pressure test the cooling system. If the system will not hold pressure and there are no external leaks the head gasket may be faulty. - Nick at Pelican Parts  
Opa Comments: Just did free-wheel test on my E 46 fan, it does not spin freely at all. Fan and clutch move together 5-10 degrees max. Does this mean the clutch is stuck in ON? Any solution beside replacing clutch? Have not experienced overheating
Thanks for your support.
March 18, 2016
  Followup from the Pelican Staff: Fan clutches should spin with resistance. Follow the steps in this article to test it. If it doesn't act the way described, replace it. - Nick at Pelican Parts  
Regan Comments: Hi there, as a frequent reader of your articles, I have taken a detailed description with photos of refilling the viscous fan hub on both E36 and E46 models. If there's an email address that I can send these to, I will happily supply. Regan.
February 14, 2016
  Followup from the Pelican Staff: You can send the info through the Pelican parts contact us page: - Nick at Pelican Parts
seanny Comments: Hi I replaced my water pump coz t was leaking and I drove 4lfor like 4hours and after that it kept complaining about low water and id add water and 10min later it needed more water... this went on for 3 hours .. what could be the problem. .. E46 325
December 2, 2014
  Followup from the Pelican Staff: You either had air trapped in the system and it wasn't full, or there is a leak. - Nick at Pelican Parts  

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Page last updated: Mon 1/22/2018 02:25:29 AM