Fan clutch test

[bimmer1527]

I am wondering how to tell if the fan clutch is working properly or not. Should the fan be spinning only when the engine/radiator is hot? I recently replaced most of the cooling system components except the clutch due to an overheating problem. I didn't think of the fan clutch at that time. After reading some related threads I got the impressoin that fan should only spin when the radiator is hot. But my fan always spins as soon as the engine starts running when the radiator is still cold. Does that mean my clutch is stuck in the engaged position all the time?

[strad]

Yes, it's normal for the fan to freewheel all the time. This does not mean there's anything wrong with the fan clutch. If you're able to stop the fan from spinning (with a rolled-up newspaper) under conditions when it should be fully engaged (like when the temperature gauge goes above the middle for example), then you've got a bad fan clutch.

If you know what you're listening for, you can tell when it's engaged by sound. I diagnosed a failed fan clutch on my 94 without even getting out of the car -- it failed fully engaged.

[94Bimm3r]

the manual clutch fan will always spin a bit at idle it has nothing to do with how hot your radiator is that is called your aux fan which is controlled on a t-stat my 94 has no clutch fan and i have never once had a problem and i auto x it here in iowa where we see a 100 degrees plus humidity soooo do you need it i dont know thats up to you. you will get mixed feelings

[shogun]

Fan Clutch test
First, lets discuss what the fan clutch does and why it is there. The fan clutch is just what the name says, it is a mechanism that will clutch the fan on and off depending on the need for more or less cooling air to flow thru the radiator. It is a thermostatically controlled device that when operating normally will vary the fan speed independently of the engine speed. When cruising down the road at freeway speeds, with outside temperature less then desert conditions, the fan should be merely be idling along, turning just fast enough to add a little air flow when needed, in this way the fan noise and drag on the engine is greatly reduced. When reducing speed, the fan clutch will sense higher temperatures thru the radiator and “clutch up” thereby increasing the fan speed to help maintain constant engine temperature. It may in fact, cycle as the temperature of the air thru the radiator changes depending on airflow. If the fan clutch operation is normal, when first starting the car, the fan clutch should “clutch up” and an increase in noise and airflow should be obvious. After about 60-90 seconds, the fan will un-clutch and the noise and airflow will drop. The fan will continue to turn but at a much reduced speed. As the engine warms and the thermostat opens to regulate the temperature, the air thru the radiator gets hotter and the clutch will sense this, thereby increasing the speed of the fan to maintain a normal operating temperature.
First signs of trouble:
A normal temperature indication at freeway speeds and an increasing temperature as the vehicle slows is one of the first indications of trouble. Many other things may give this indication but if the temperature seems to be stable at speeds but climbs in traffic or while stopped, this is a good indication that the fan clutch isn’t working correctly. As the temperature continues to climb, the auxiliary electric fan should start but may not provide enough air to keep the engine from overheating.
Another sign of trouble is if the fan noise is high and never decreases after starting, and is there anytime the engine RPM is higher then idle, this means that the fan clutch is “frozen” and is not releasing. Although this will not result in immediately serious trouble, it will load the engine continually and gas MPG will be reduced. Load on the fan belt(s) will be higher and shorten the life of that component also.
Fan modifications:
It has been suggested that other models of BMW fans can be substituted to reduce the noise and load of the fan. This is NOT recommended! If the fan clutch is working properly, there should be no need to replace with a lesser fan. The noise and load of the fan should only be there when it is “clutched up” and the fan speed needed to keep that big V-12 cool. BMW designed it this way and it is never a good idea to alter the cooling system and in particular where alloy engines would be effected.
Testing the fan clutch:
If you have reason to suspect that the fan clutch is defective, here is the recommended procedure to verify the condition of the fan clutch.
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”.

written by MWrench
http://www.mwrench.com/

[bimmer1527]

Thanks for the detailed writeup exactly what I was looking for.

[mrf]

Fan Clutch test
First, lets discuss what the fan clutch does and why it is there. The fan clutch is just what the name says, it is a mechanism that will clutch the fan on and off depending on the need for more or less cooling air to flow thru the radiator. It is a thermostatically controlled device that when operating normally will vary the fan speed independently of the engine speed.

There doesn't seem to be an electrical connection between the radiator temp switch and my mechanical fan's clutch in my E36. Am I just not looking hard enough? It seems there is no active logic that governs when the fan's clutch tightens up when additional cooling is required etc.

Reason I'm bumping this thread is because I need some guidance on my clutch fan that seems to be stuck/frozen/seized etc. Before I could freespin the fan with the engine off, but now the clutch is locked in a 'direct drive' state and its RPM matches that of my water pump pulley at a ratio of 1:1. This causes LOT of noise as air is pulled through the rad at elevated engine speeds and frankly, sounds abnormal. I'm also afraid of the fan exploding due excessive RPM. The clutch doesn't seem to 'unclutch'. What controls this 'unclutch' mechanism?

[JDStrickland]

There doesn't seem to be an electrical connection between the radiator temp switch and my mechanical fan's clutch in my E36. Am I just not looking hard enough? It seems there is no active logic that governs when the fan's clutch tightens up when additional cooling is required etc.

Reason I'm bumping this thread is because I need some guidance on my clutch fan that seems to be stuck/frozen/seized etc. Before I could freespin the fan with the engine off, but now the clutch is locked in a 'direct drive' state and its RPM matches that of my water pump pulley at a ratio of 1:1. This causes LOT of noise as air is pulled through the rad at elevated engine speeds and frankly, sounds abnormal. I'm also afraid of the fan exploding due excessive RPM. The clutch doesn't seem to 'unclutch'. What controls this 'unclutch' mechanism?

There is no electrical connection, none, not any, between the Fan Clutch and any other sensor. Or any thing else for that matter.

The Fan Clutch has two plates and some jelly inside. This is also called a Viscous Couple. The jelly gets hot and expands, locking the plates so that the fan is positively driven. When the jelly cools, the plates separate and the fan is only driven by the viscous nature of the jelly itself.

If one uses a rag folded to several layers and CAREFULLY introduces it to the outboard edge of the spinning fan, one could stop the fan from turning when the engine is cold. One would be an idiot to do this, but the theory holds true without regard to the intelligence of the person doing this test.

When the vehicle is not moving or is moving slowly, as in stop-n-go traffic, the heat in the radiator builds, this increases the heat exposed to the viscous couple, which expands the jelly and locks the plates and drives the fan to physically pull air through the radiator to keep it cool. When the vehicle speed increases, the couple cools because of the air being forced through the radiator, keeping the radiator cool so the fan is no longer needed. The fan is no longer being driven by the belt system, it is merely spinning due to the viscous material having drag by the very nature of the jelly.

Back to the folded rag...

If one was silly enough to stop the fan from spinning, then one would then spin the fan backwards -- against the direction of travel -- and if the fan spun freely then this would indicate that couple was toast. If the fan reversed for the travel of a few blades then went in the normal direction, then the couple is good. If the fan is very difficult to stop, then the couple is good. If the fan is impossible to stop, then the couple is locked all of the time. As the engine warms, stopping the fan should become an increasingly difficult, and stupid, task.

The fan, engine off, should be able to be turned, but not spin freely. It should be tight and smooth. If you cannot turn the fan because it is locked to the pully, then the couple is shot.

Normally, the couple fails in the free mode, not the locked mode. The typical symptom is that the car heats in stop-n-go traffic, but cools again when the traffic starts moving. This is because the airflow through the radiator is lost when the couple fails to lock, then as the car speeds up the airflow increases with the speed.

The downside to a constant locked fan clutch is that it is being driven when it is not needed, and this takes energy, which is gasoline. It is not very much gas on a single car, but when there are millions upon millions of cars with the same kind of fan, the fuel savings over the entire fleet is considerable. This is why they put them in our cars. Some will say that the fan is noisy, I'm not sure I believe this. There are so many other noises that I cannot separate the fan from the others, so it is not an issue, if you ask me.

[mrf]

Thanks JDStrickland. My VC is stuck in the locked mode. This causes the fan to pull an absolutely absurd amount of air which generates a lot of noise. While the noise above 4000RPM sounds abnormal, I'm not as worried about the noise as I am about the fan blades spinning faster than they were designed to do and come apart at high RPM. Don't care so much about the increased fuel consumption but I don't want to stuck on the side of the road because there's a gaping hole in my radiator and/or hoses because the fan blades disintegrated at 7000RPM.

For the short term, I am going to remove the mechanical fan/clutch and will reevaluate when spring rolls around. The little pusher fan in front of the A/C condenser seems capable of pushing a decent amount of air as well.

EDIT - Didn't want to bump this thread, so I'll just edit this post. I removed just the fan blades as it was much easier and cheaper (free) than getting the right 32mm wrench and bracket to remove the clutch. Just had to try a few different hex keys till one fit and slowly/painstakingly removed the fan while leaving the clutch on there.

[JDStrickland]

Well, Pittsburgh is a good place to not have a fan, I suppose. I would not go without a fan where I live because even though it rained yesterday, and is cold today (low 60s), it can be 85 next week, and a missing fan would be problematic.

PS
Temps below 70 cause me to dust off my sweatshirt collection and layer my leather jacket. Cold is relative...

[Luckys]

First off, Hello and I apologize for my first thread being a resurrection, but my question pertains directly to this information. I am a new and first time BMW owner and so far I'm very happy. Car is a 2008 328i Sedan with 69k. On the test drive I noticed the loud fan, which the dealer told me was normal. I've since read a ton on it and can see a divide where some people say its normal and some say its not. Here's my specific question; I've read this thread and tried the clutch newspaper test. However, I didn't see a diagnosis for this specific question....when the engine is cold and first started I am not able to stop the fan with a newspaper. I assume that means the clutch is engaged even when cold. Does that mean the clutch is bad? And if it is bad would that be what's making it so loud?? Thanks in advance adn happy memorial day to you all!! Shaun

[sjpgoalie]

First off, Hello and I apologize for my first thread being a resurrection, but my question pertains directly to this information. I am a new and first time BMW owner and so far I'm very happy. Car is a 2008 328i Sedan with 69k. On the test drive I noticed the loud fan, which the dealer told me was normal. I've since read a ton on it and can see a divide where some people say its normal and some say its not. Here's my specific question; I've read this thread and tried the clutch newspaper test. However, I didn't see a diagnosis for this specific question....when the engine is cold and first started I am not able to stop the fan with a newspaper. I assume that means the clutch is engaged even when cold. Does that mean the clutch is bad? And if it is bad would that be what's making it so loud?? Thanks in advance adn happy memorial day to you all!! Shaun

You have an e90. This is the E36 section. I would start a new thread in that subforum. I thought yours was electric, not mechanical.

[Luckys]

You have an e90. This is the E36 section. I would start a new thread in that subforum. I thought yours was electric, not mechanical.

Will do. Thanks for the reply.

[scoobiedoo2029]

the test is to see how long it takes you to install an electric fan before your plastic one on the car now explodes.

[anarekist]

There are so many other noises that I cannot separate the fan from the others, so it is not an issue, if you ask me.

thanks for the explanation, i feel smarter. is there a way to manually lock the fan? i have the fan with the outer ring from a diesel motor so not worried about blades flying off.

[JDStrickland]

thanks for the explanation, i feel smarter. is there a way to manually lock the fan? i have the fan with the outer ring from a diesel motor so not worried about blades flying off.

Manually lock the fan? Short of driving a bolt through it, I don't believe you can lock the fan. (On an offroad trip in the desert once, one of the Jeeps had the clutch fail and the fan was free-wheeling all of the time resulting in an engine overheat condition. We removed one of the bolts that holds the fan to the clutch and installed a longer bolt to the fan would be fixed to the pulley. This made the fan move air again, but the guy that onwed the Jeep had to buy a new fan clutch when he got home.)

I suppose if you were out on the highway and the clutch failed so that the fan never pushed air, you could do the same thing that we did on the Jeep, but if you are on the highway I'm not sure how you would even know that the clutch had failed, and you would not bother to pull over and put a longer bolt in. The whole point of the fan is to move air when the vehicle is standing still or moving slowly -- like when a Jeep is hill-climbing in the sand in the desert on a 100-degree day, conditions that your BMW might experience in stop-n-go traffic that is mostly stopped -- but when the vehicle speed increases to 30-ish MPH or more, the air flow caused by vehicle motion should be sufficient to cool the engine. There are people in the BMW family that remove the fan, you are asking how to make it work all of the time that the engine is running.

I'm not sure why one would want to defeat the fan clutch for most normal vehicle operations.

[anarekist]

if the fan is always engaged then i wouldnt have to worry, ever. i dont own a fleet of cars so the gasoline wasted in my lifetime is no a concern. anways just wondering.

[Turbohugh]

if the fan is always engaged then i wouldnt have to worry, ever. i dont own a fleet of cars so the gasoline wasted in my lifetime is no a concern. anways just wondering.

A locked fan that doesnt disengage will likely explode if not replaced/repaired.

From my observations, when working correctly it disengages or freewheels above 3-4k rpms.

My fan is noisy below 3k (I can hear it) however it 'goes away' over 3k .>

[dvspider]

I'm a brand new user of this site and I posted my overheating problem somewhere else on here I guess. But after somebody replied and said it sounded like a bad fan clutch I was directed here. My 2000 BMW 328i, never overheated in the winter time (when i bought it) where it was always 40 degrees-65degrees. Now that summer is here, today (88 degrees), the gauge went all the way to the red in slow or stopped traffic. I noticed the loud fan when I bought it and I have no idea how well it was maintained before I bought it but here are the symptoms: loud fan at idle (sounds like an aircraft turbine), smoke came through the vents today when the AC was on and then went away when it was turned off. After that the A/C cold air came and went, weird spinning noise could be heard near the dash (engine area nearest steering wheel) and then when I got it onto the highway the gauge returned to normal spot. I think with the higher temps now that this will become a constant and problematic. Does all this sound like a bad fan clutch or signs of bigger problems? Sorry for my ignorance with all this but I'm doing my best to understand (admittedly I'm a noob, novice, FNG, BMW owner and mechanic) Also I have limited money because my wife has maximum spending habits =)

[shogun]

2000 328i? E36? Or E46? I assume your car is probably a E46.
Anyway, I assume the loud fan you noticed is the auxiliary fan at stage 2, = high speed. That is an electric fan and always runs in stage 1 = low speed when AC is on, and switches to high speed when a certain temperature at the temperature feeler at the radiator is reached. Simply explained.
That is this fan, here an example from the E34
http://www.bmw4life.com/auxFanR.htm
http://www.nmia.com/~dgnrg/page_20.htm
But in addition your E46 has also a visco fan clutch as we discussed before, and that is apparently not good anymore, see how to test in my post above.
The part number is shown here
http://bmwfans.info/parts/catalog/E4..._fan_coupling/

item # 2 Fan coupling 11527505302 For vehicles with: Automatic transmission (S205A) = Yes

also fits:bmw fan clutch part# 11527505302 fits m3, m5, x5, 3.0i, 2.3, 320i sedan 1989-2006

Dealer is asking >>$100, on the internet you get a lesser premium brand one for around 40-70, a good brand Behr will be around $100.

Or a Meyle, SKU #:11527505302MY Part:Fan ClutchOE Numbers:11527505302, 11521709499, 11521719046, 11521719269, 11521740963 for around $80

To find out what model and built year/month your car is, check here with your VIN

http://www.bmwarchiv.de/vin/bmw-vin-decoder.html
Then add that to your profile, model, engine, month/year helps us to help you.

[Type1Kicks]

Great write up

Fan Clutch test
First, lets discuss what the fan clutch does and why it is there. The fan clutch is just what the name says, it is a mechanism that will clutch the fan on and off depending on the need for more or less cooling air to flow thru the radiator. It is a thermostatically controlled device that when operating normally will vary the fan speed independently of the engine speed. When cruising down the road at freeway speeds, with outside temperature less then desert conditions, the fan should be merely be idling along, turning just fast enough to add a little air flow when needed, in this way the fan noise and drag on the engine is greatly reduced. When reducing speed, the fan clutch will sense higher temperatures thru the radiator and “clutch up” thereby increasing the fan speed to help maintain constant engine temperature. It may in fact, cycle as the temperature of the air thru the radiator changes depending on airflow. If the fan clutch operation is normal, when first starting the car, the fan clutch should “clutch up” and an increase in noise and airflow should be obvious. After about 60-90 seconds, the fan will un-clutch and the noise and airflow will drop. The fan will continue to turn but at a much reduced speed. As the engine warms and the thermostat opens to regulate the temperature, the air thru the radiator gets hotter and the clutch will sense this, thereby increasing the speed of the fan to maintain a normal operating temperature.
First signs of trouble:
A normal temperature indication at freeway speeds and an increasing temperature as the vehicle slows is one of the first indications of trouble. Many other things may give this indication but if the temperature seems to be stable at speeds but climbs in traffic or while stopped, this is a good indication that the fan clutch isn’t working correctly. As the temperature continues to climb, the auxiliary electric fan should start but may not provide enough air to keep the engine from overheating.
Another sign of trouble is if the fan noise is high and never decreases after starting, and is there anytime the engine RPM is higher then idle, this means that the fan clutch is “frozen” and is not releasing. Although this will not result in immediately serious trouble, it will load the engine continually and gas MPG will be reduced. Load on the fan belt(s) will be higher and shorten the life of that component also.
Fan modifications:
It has been suggested that other models of BMW fans can be substituted to reduce the noise and load of the fan. This is NOT recommended! If the fan clutch is working properly, there should be no need to replace with a lesser fan. The noise and load of the fan should only be there when it is “clutched up” and the fan speed needed to keep that big V-12 cool. BMW designed it this way and it is never a good idea to alter the cooling system and in particular where alloy engines would be effected.
Testing the fan clutch:
If you have reason to suspect that the fan clutch is defective, here is the recommended procedure to verify the condition of the fan clutch.
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”.

written by MWrench
http://www.mwrench.com/

[Nanniepoo]

I'm a brand new user of this site and I posted my overheating problem somewhere else on here I guess. But after somebody replied and said it sounded like a bad fan clutch I was directed here. My 2000 BMW 328i, never overheated in the winter time (when i bought it) where it was always 40 degrees-65degrees. Now that summer is here, today (88 degrees), the gauge went all the way to the red in slow or stopped traffic. I noticed the loud fan when I bought it and I have no idea how well it was maintained before I bought it but here are the symptoms: loud fan at idle (sounds like an aircraft turbine), smoke came through the vents today when the AC was on and then went away when it was turned off. After that the A/C cold air came and went, weird spinning noise could be heard near the dash (engine area nearest steering wheel) and then when I got it onto the highway the gauge returned to normal spot. I think with the higher temps now that this will become a constant and problematic. Does all this sound like a bad fan clutch or signs of bigger problems? Sorry for my ignorance with all this but I'm doing my best to understand (admittedly I'm a noob, novice, FNG, BMW owner and mechanic) Also I have limited money because my wife has maximum spending habits =)

It sounds like you kept driving with your coolant temp in the red...please please tell me this isn't true....

While the loud fan does sound like a bad clutch, it sounds like it should have been locked, and considering it was locked, the fan shouldn't have been the cause of you overheating. So your problems are bigger than just the fan clutch. I don't know if E46's are as sensitive to overheating as E36's, but you may very well have blown your head gasket by continuing to drive it....you might want to utilitize the E46 subforum, because those users would be better able to help. Honestly I don't even know if E46's have a fan clutch or they moved to an electric fan...

[JoeBimmmer]

Just as an aside, I had a 2000 323Ci (E46) CPO car bought from dealer. It did not have an engine driven (belt drive) fan, just the electric fan in front of the radiator. It had ~17,000 when I got it and somewhere north of 100,000 when I let it go. It never overheated in heavy slow traffic, never overheated on trips across the southwest in summer. I don't know if the fan had been removed by the PO or even if it had one to begin with. Would BMW CPO a car without a needed piece of cooling? Who knows? Anyway I drove it seven or eight year sans fan. The next owner did replace the electric fan about three years after he had it . . . . the electric fan wanted to run all the time. Fan trivia FWIW.

[M3C]

Is it of any importance how the fan clutch is stored, direction up or down or on a side before it is mounted?
What is an average life expectancy of a fan clutch?

[shogun]

On my E32 750iL the original fan clutch lasted from 1988-2011.

Here copied from ZF about storage:

Fan clutches: Function and handling

Important Service Bulletin Fan clutches: Function and handling
Hints for experts
Overview
The SACHS fan clutch assists the engine to maintain its correct operating temperature. When the engine temperature exceeds a certain level, the fan clutch is activated causing additional air flow through the radiator. The fan clutch is activated when hot air passes over a bi-metal strip 1 on the fan clutch, causing deformation of the bi-metal strip which activates the control pin 2. The control pin opens the valve 3 allowing silicone oil 4 to enter the drive chamber of the fan clutch. The temperature controls the speed of the fan clutch i. e. higher temperature causes higher speed. As temperature decreases, so does the speed of the fan clutch.

Transport and Storage
To ensure proper function of the fan clutch we recommend that these instructions be followed. It is most important that the fan clutch be positioned correctly during transportation and storage. Please note the arrow on the fan clutch package. The fan clutch should be stored either vertically but preferably flat with the arrow pointing up. This is to ensure that silicone oil does not leak past the control pin seal. Should a small amount of oil leak past the control pin seal due to incorrect storage, the fan clutch will still perform correctly.

Attention:
Fan clutches must be stored flat in the box with the arrow pointing up.

Warning: Please note that the bi-metal strip on the front of the clutch has been calibrated to perform at a particular temperature range. Changing the position of this strip will change the
performance of the fan clutch.

avoid injury – keep clear of fan and pulleys when engine is running.

Service information
Fan clutches are often replaced even though they are performing correctly. In order to diagnose a cooling system problem, it is recommended that the following be checked:

Check the coolant level.

Check the temperature gauge.

Check that radiator fins are free from dirt and insects.

Check the proper operation of the thermostat.

Check the fan belt.

Check the operation of the water pump.

Check if sufficient hot air can flow through the radiator to activate the fan clutch.

Check for blockages inside the radiator preventing flow of coolant.

Check that the fan is the correct type and undamaged.

Noise generated by the AC clutch or by the engine should be investigated.

Fitting Instructions:
Adjust water pump drive belt to specification (do not overtighten).

Unscrew fan clutch from spindle 6.
Caution Mercedes Benz applications. Check the direction of rotation of the fan. The direction of rotation is also shown on the mounting flange. The engine side of the fan clutch required to be mounted to the spindle is marked accordingly. Radiator fins are of solid material 7.
1) An anti clockwise (left hand) rotating clutch has a right hand threaded nut.
2) A clockwise (right hand) rotating clutch has a left hand threaded nut.
Note:
To ensure that the correct part number is fitted for the vehicle application see application list.

All bolts should be tightened to recommended torque (MB 10 Nm / BMW 12 Nm).
(Mercedes Benz mark „Vorne Front“ in the direction of travel).

Tighten the fan clutch onto spindle with the specified torque
(DB 45 Nm / BMW 40+10 Nm).

[shogun]

And here a vintage Mercedes Benz info from 1968 with instructions and info how to install the OPTIONAL extra visco fan clutch http://www.roststopp.de/strichacht/d...plung-1968.pdf

Einbauanleitung fuer Sonderausstattung

The most important is this:

Pruefen der Viskokupplung:

Beim Kaltstart des Motors laeuft die Viskokupplung zunaechst mit erhoehter Drehzahl bis das Oel in der Viskokupplung aus dem Arbeitsraum in den Vorratsraum zurueckgeflossen ist. Circa 1-3 Minuten.
Danach schaltet die Luefterkupplung ab und die Luefterdrehzahl sinkt auf etwa 25-30% der Antriebsdrehzahl. Die Kuehlleistung des Motors ist hierdurch absichtlich herabgesetzt, sodass der Motor seine Betriebstemperatur moeglichst schnell erreicht.Durch das Ansteigen der Kuehlertemperatur wird ueber den Bimetallstreifen , der vorne an der Visko-Luefterkupplung angebracht ist, die Luefterkupplung zugeschaltet, d h. mit steigender Kuehlertemperatur nimmt auch die Luefterleistung zu, die aber nie die gleiche Drehzahl wie der Motor erreicht im Endeffekt. Laesst man den Motor nur kurz laufen und stellt ihn noch mit kaltem Motor wieder ab, so muss sich der Luefter mit relativ geringem Kraftaufwand von Hand durchdrehen lassen. Die Kupplung ist dann voll abgeschaltet. Die volle Zuschaltung der Kupplung wird erreicht, wenn die aus dem Kuehler austretende Kuehlluft mindestens eine Temperatur von ca. 62 Grad erreicht hat.

translated:



Checking the viscous coupling :

During a cold start of the engine the viscous coupling will initially run at increased speed until the oil in the viscous coupling flowed back from the working space in the storage space. Approximately 1-3 minutes.
Thereafter, the fan clutch switches off and the fan clutch speed decreases to about 25-30% of the engine speed/RPM. The cooling capacity for the engine is thereby deliberately reduced so that the engine operating temperature is reached as fast as possible . By the increase of the coolant temperature the bimetallic strip which is attached to the front of the viscous fan clutch changes the speed of the fan clutch , that means, with increasing coolant temperature also the fan clutch speed increases , but never the same speed as the engine reaches in the end .
When the engine is started cold and only run for a short period while still cold, then it must be possible to turn the fan clutch with relatively little effort by hand when engine is switched off.
The fan clutch coupling is then switched off completely . The full engagement of the clutch is obtained when the air passing thru the radiator has reached a minimum temperature of about 62 degrees Celsius.