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Discussion Starter #1
As we all know, the fan clutches on these cars often fail, sometimes catastrophically.

On Friday I noticed a ton of play in my fan assembly (water pump shaft ok) and realized mine was gone. It was not locked up but very wobbly and stiff to rotate.

I ordered a replacement online (not OEM as I am dumping a ton of cash into my other project and $200 wasn't in the cards) from Amazon for Sunday delivery. It is a URO PARTS clutch, and it was specified for all M62 and S62 vehicles.

Installed the clutch and it seems to be ok. It tests fine with the newspaper test when the engine is cool. When the engine is hot, the fan seems to be fully coupled.

My concern is that the fan speed seems to really increase with revs once the engine is hot. I was under the impression that the clutch also prevented the fan from spinning too quickly and grenading....

Does anyone know if the clutch is supposed to limit fan RMP from rising with the water pump output shaft, or is it normal for the fan to spin at engine RPM once it is thermally coupled?

I have ordered a new fan assembly for safety's sake, but it is not here yet. I'm suddenly cautious to rev the car as i am not sure if this new clutch is working correctly.
 

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IIRC, the fan spools up with the engine rpm to about 3k RPM only in first and second gear. Not sure if this is what you're looking for. I'm sure someone more knowledgeable will chime in.
 

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Discussion Starter #3
IIRC, the fan spools up with the engine rpm to about 3k RPM only in first and second gear. Not sure if this is what you're looking for. I'm sure someone more knowledgeable will chime in.
See, that was my understanding for some reason. I *think* mine is hooked up beyond 3K.... Not liking that idea.

Thanks!
 

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IIRC, the fan spools up with the engine rpm to about 3k RPM only in first and second gear. Not sure if this is what you're looking for. I'm sure someone more knowledgeable will chime in.
I believe this is correct (although I hadn't heard about the first and second gear only part - In fact, you can test it in the garage without any gear engaged from my experience) As the engine gets hot the fan will be more and more tightly "coupled" with the engine speed but only up to the 3k rpm if it is functioning correctly. If you are convinced that the fan continues to stay coupled above 3k then that will not end well for you. Should be pretty easy to test since the fan is so loud at that rpm.
 

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I believe the fan clutch is designed to operate for the first two minutes of operation and temps above 79C.

It uses a viscous (oil filled) clutch that locks it above these temps. I think the exploding clutches are probably really just exploding plastic fans, though I haven't had direct experience with this. If the viscous clutch fails, the fan will simply not lock and therefore you will get no flow.
 
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Discussion Starter #7
I believe the fan clutch is designed to operate for the first two minutes of operation and temps above 79C.

It uses a viscous (oil filled) clutch that locks it above these temps. I think the exploding clutches are probably really just exploding plastic fans, though I haven't had direct experience with this. If the viscous clutch fails, the fan will simply not lock and therefore you will get no flow.
Agreed, the clutches are not exploding, but when they fail, the fan is spun at RpMs beyond its tolerance and it grenades.

I guess what I am asking at the end of the day is whether or not the fan is locked to RPM once the temp threshold has been met? If not, at what point is the fan clutch slipping so as not to exceed X RPM?

I feel like mine might be spinning too much...
 

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I don't think it's possible for it to go too fast. When the clutch fails, it's due to the fluid leaking out. No fluid means no clutch operation. I have not heard of one just locking up (not that it hasn't happened), but even if it did, the clutch would simply always be active and locked to engine rpm? In any event you can test your clutch pretty easily if you haven't.

Testing for a bad Fan Clutch (Sachs and Behr))
 
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I don't think it's possible for it to go too fast. When the clutch fails, it's due to the fluid leaking out. No fluid means no clutch operation. I have not heard of one just locking up (not that it hasn't happened), but even if it did, the clutch would simply always be active and locked to engine rpm? In any event you can test your clutch pretty easily if you haven't.

Testing for a bad Fan Clutch (Sachs and Behr))
We are talking about two different types of failure. Yes, the clutch can fail in such a way as to be too loose and not "clutch up" which results in inadequate airflow pulled through the radiator and high operating temperatures. This type of failure is not immediately catastrophic but can be damaging if the coolant or engine overheat as a result. But this is not what the OP is asking about.

The other type of failure that the OP is referring to is when the clutch basically seizes to the engine and does not regulate it's rotational speed. It simply turns as fast as the engine. The plastic fans are not designed to turn upwards of 7000 rpm and numerous posts on this board have recounted the very sudden damaging effect of a fan "grenading" due to excessive speed causing damage to hoses, radiators and even hoods.

A simple test would be to 1) bring the vehicle up to operating temperature 2) Raise the hood (makes it a little easier to hear) and somewhat slowly raise the rpm to about 3k. Most likely you will be able to easily hear the fan roaring at this point. Also take note as to whether the increase in fan noise is directly proportional to the increase in engine rpm. 3) Now give her some more juice to get the engine up to 4500 or so. If the fan increases to 4500 also, it will be very loud indeed and this would be a strong indication of the clutch not performing properly.

When I do this, the fan will increase to 3000 but will actually drop off even as I hold the rpm at 3000. I.e. the clutch starts to loosen to avoid overspeed. Raising the rpm further results in no additional fan noise, just more engine music.

By the way, I'm no mechanic, but I am familiar with both types of failure. Seems to me if your really concerned you could get a professional to give her a listen if you don't trust your own diagnosis.
Good Luck.
 

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Discussion Starter #10
We are talking about two different types of failure. Yes, the clutch can fail in such a way as to be too loose and not "clutch up" which results in inadequate airflow pulled through the radiator and high operating temperatures. This type of failure is not immediately catastrophic but can be damaging if the coolant or engine overheat as a result. But this is not what the OP is asking about.

The other type of failure that the OP is referring to is when the clutch basically seizes to the engine and does not regulate it's rotational speed. It simply turns as fast as the engine. The plastic fans are not designed to turn upwards of 7000 rpm and numerous posts on this board have recounted the very sudden damaging effect of a fan "grenading" due to excessive speed causing damage to hoses, radiators and even hoods.

A simple test would be to 1) bring the vehicle up to operating temperature 2) Raise the hood (makes it a little easier to hear) and somewhat slowly raise the rpm to about 3k. Most likely you will be able to easily hear the fan roaring at this point. Also take note as to whether the increase in fan noise is directly proportional to the increase in engine rpm. 3) Now give her some more juice to get the engine up to 4500 or so. If the fan increases to 4500 also, it will be very loud indeed and this would be a strong indication of the clutch not performing properly.

When I do this, the fan will increase to 3000 but will actually drop off even as I hold the rpm at 3000. I.e. the clutch starts to loosen to avoid overspeed. Raising the rpm further results in no additional fan noise, just more engine music.

By the way, I'm no mechanic, but I am familiar with both types of failure. Seems to me if your really concerned you could get a professional to give her a listen if you don't trust your own diagnosis.
Good Luck.
This sounds more like the line of thought I am having. I need someone to bring the revs up to determine if we are spinning beyond that 3k point. As of right now, I am not certain if I am just being overly cautious as it sounds like a bloody cessna under there (not out of the ordinary, though).

And to speak to my OEM fan clutch, it actually failed and did not lock. The fan would spin and you could spin it freely by hand, but the clutch assembly was wobbling on the clutch shaft (forward of locking buy

Either way, I will take a real good listen to see if this thing is making more noise beyond 3-4k or if it levels off. Thank you for the suggestions
 

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Discussion Starter #11
I don't think it's possible for it to go too fast. When the clutch fails, it's due to the fluid leaking out. No fluid means no clutch operation. I have not heard of one just locking up (not that it hasn't happened), but even if it did, the clutch would simply always be active and locked to engine rpm? In any event you can test your clutch pretty easily if you haven't.

Testing for a bad Fan Clutch (Sachs and Behr))
I have tested the fan and it passes this test....

What I am uncertain about is whether or not the clutch is preventing the fan from spinning TOO fast. As I understand it, part of the function is to 'slip' (for lack of a better word) so the fan does not spin as fast as the engine at all times.

The incidence of failure of these plastic fans probably increases significantly with sustained high RPM operation. Keeping the fan around 3K even if the engine is spinning faster is one of the jobs of the clutch, no?
 

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The overspeed failures were because the clutch internal bearings ran out of lube and locked up, preventing slippage, and spun the fan at water pump speed. The plastic blades, no doubt a bit embrittled by heat and age, then broke up.

So if you can stop the fan with a rolled-up newspaper when KTMP's (obtained from the secret menu) are 79C or less, the clutch bearings are OK and you don't have to worry.

The fan clutch doesn't engage until the air coming through the rad is about 95C. The aux electric fan is the primary cooling fan and the clutch fan is the back-up fan that kicks in if the heating loads get too high for the aux fan.
 

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This thread now makes me wonder about my fan/clutch.... My car is a '01, and think it's the original fan/clutch assembly with 127K miles on it. I will do the test this week end as recommended in the tread but then what?? (assume it's bad).

The choices seem:
1. Replace with new
2. Rebuild clutch install new fan
3. Just rebuild clutch
4. remove both and convert to electric fan.

RealOEM says around $250 for parts (though RealOEM usually seems a little low) for a new fan/clutch
RK Automotive ($525) or Zionville conversion kits (includes a radiator... $1200) or even Tim May's dual Chevy Malibu Trimline on a RK shroud ($???) (http://www.m5board.com/vbulletin/e39-m5-e52-z8-discussion/237065-radiator-fan-shroud-revamp-dual-fan-setup.html ) are the examples of the conversion approach.

So, on balance for NA engines, is the dumping the 10 to 15 year old fan for a new replacement good enough?? Does the grenadeing of the fan risk go down so dramatically, it's acceptable?? Or is the clutch design just that bad that it's not the years or the mileage, but just ones luck to have it go at any given moment??

Or is the conversion just better, period?? and thus the recommended solution??

Also, based on 68FB info that the engine fans is the secondary air movement source, would that still be true with a conversion or do the two front fans go away with a electric conversion??

This has been a very timely and interesting thread... thanks one and all
 

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Discussion Starter #15 (Edited)
This thread now makes me wonder about my fan/clutch.... My car is a '01, and think it's the original fan/clutch assembly with 127K miles on it. I will do the test this week end as recommended in the tread but then what?? (assume it's bad).

The choices seem:
1. Replace with new
2. Rebuild clutch install new fan
3. Just rebuild clutch
4. remove both and convert to electric fan.

RealOEM says around $250 for parts (though RealOEM usually seems a little low) for a new fan/clutch
RK Automotive ($525) or Zionville conversion kits (includes a radiator... $1200) or even Tim May's dual Chevy Malibu Trimline on a RK shroud ($???) (http://www.m5board.com/vbulletin/e39-m5-e52-z8-discussion/237065-radiator-fan-shroud-revamp-dual-fan-setup.html ) are the examples of the conversion approach.

So, on balance for NA engines, is the dumping the 10 to 15 year old fan for a new replacement good enough?? Does the grenadeing of the fan risk go down so dramatically, it's acceptable?? Or is the clutch design just that bad that it's not the years or the mileage, but just ones luck to have it go at any given moment??

Or is the conversion just better, period?? and thus the recommended solution??

Also, based on 68FB info that the engine fans is the secondary air movement source, would that still be true with a conversion or do the two front fans go away with a electric conversion??

This has been a very timely and interesting thread... thanks one and all

Just as an FYI, i joined the 200K mile club a couple weeks back and this appeared to be the OEM fan clutch and fan. I have a new fan coming to complete the repair and to be safe. I have thought about an electric fan and aluminum rad setup, but that would probably be part of an SC project in the next year or so.

Right now I am swapping an LS motor into my Grand Wagoneer and the full custom aluminum rad was only $450. Another $250 for dual electric fans and shroud. Tough to swallow $1200 for the same setup on the M, but in the end, probably worth it. I have had 2 cooling system failures on this car and two more on my old 540i/6 before it. Pretty sure this wont be the last cash I throw down the cooling system sinkhole!
 

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Don't worry man! If your pusher fan and clutch fan are working properly, you shouldn't have any overheating issues on an NA S62. Even our FI cars do fine for the most part. It's the summertime Cali days that are a bummer.
 

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Don't worry man! If your pusher fan and clutch fan are working properly, you shouldn't have any overheating issues on an NA S62. Even our FI cars do fine for the most part. It's the summertime Cali days that are a bummer.
LOL!! Yep, that's 99.999% of time not a worry here in MN... :1: Thanks...
 

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The aux electric fan is the primary cooling fan and the clutch fan is the back-up fan that kicks in if the heating loads get too high for the aux fan.
I don't want to argue with someone way more experienced than I am, but this statement doesn't make sense to me. Auxiliary is defined as "supplementary, Reserve, used as a substitute" per dictionary.com. Therefore, it stands to reason that the auxiliary electric fan is the reserve fan. By contrast, the mechanical fan is always turning and always pulling air (sometimes more, sometimes less depending on the level of clutch engagement) whether or not the electric fan is on. Therefore, the mechanical fan is the "primary" or first line of cooling defense. My car is blessed with a very efficient cooling system and the auxiliary fan never even comes on unless I have the air conditioning on (it does work).

The only reason I bring it up is so that people don't become confused as to which one is the workhorse and come to the erroneous conclusion that as long as the electric fan is working, there is nothing to worry about.
 

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I don't want to argue with someone way more experienced than I am, but this statement doesn't make sense to me. Auxiliary is defined as "supplementary, Reserve, used as a substitute" per dictionary.com. Therefore, it stands to reason that the auxiliary electric fan is the reserve fan. By contrast, the mechanical fan is always turning and always pulling air (sometimes more, sometimes less depending on the level of clutch engagement) whether or not the electric fan is on. Therefore, the mechanical fan is the "primary" or first line of cooling defense. My car is blessed with a very efficient cooling system and the auxiliary fan never even comes on unless I have the air conditioning on (it does work).

The only reason I bring it up is so that people don't become confused as to which one is the workhorse and come to the erroneous conclusion that as long as the electric fan is working, there is nothing to worry about.
Yes, the term "auxiliary" confused me too. But I am confident the clutch fan is actually the backup fan. The aux fan starts up when the rad outlet temp (lower hose) gets up to around 74C (leaving a/c out of it). I base that on a cracked DME table posted on here a while back that showed that as the aux fan startup temp. Also I have done some testing and got the same result. And TIS says the fan clutch doesn't engage until the air passing over it gets to 95C. I have also seen that in practise. I only run the clutch fan now as the new OEM aux fan was horribly noisy and kept coming on and off.

Try an experiment. Get the car up to temp (79C) in the driveway. At around 79C the aux fan will come on to get some air flow across the rad. Try the rolled up newspaper test on the clutch fan. It will stop easily. It's not doing anything.
 
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