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  #1  
Old 08-05-2006, 03:33 AM
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Proper behavior of fan clutch

I just replaced the fan clutch on my '96 E300D because the old one was just free-wheeling all the time and it kept spinning for quite a while after shutting off the engine. I noticed the new one is a lot stiffer and now I can definitely hear the fan roar when accelerating. And when turning off the engine the fan stops spinning immediately as I believe it should. What I'm puzzled about is the stiffness of the fan that doesn't seem to change with temperature. With the engine cold (and off of course) the fan exhibits the same moderate resistance to rotation as it does with the engine hot (90-100C). Is this proper or did I get a defective clutch? I was expecting the fan to be a lot looser when cold and a lot stiffer when hot.
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  #2  
Old 08-05-2006, 04:39 AM
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I read about MB fan clutches sometime ago but I can't find the source. Something like when you start a dead cold engine the fan kicks in for a few seconds until the fluid distributes then it freewheels. Eventually the engine gets hot enough for the fan to engage again. There's a minimum looseness to the fan. Even in freewheeling mode it will spin only so much when you shut off the engine. If you shut off the engine with the gauge showing 115*C then the fan will pretty much stop with the engine.

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  #3  
Old 08-05-2006, 06:01 AM
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Quote:
Originally Posted by DieselAddict
I noticed the new one is a lot stiffer and now I can definitely hear the fan roar when accelerating. And when turning off the engine the fan stops spinning immediately as I believe it should.
DA, this all sounds correct. I changed mine a few weeks ago. Mine was locked up nearly all the time creating a ton of noise (drag). If the fan freewheels, it's shot.
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Old 08-05-2006, 01:58 PM
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Quote:
Originally Posted by uberwgn
DA, this all sounds correct. I changed mine a few weeks ago. Mine was locked up nearly all the time creating a ton of noise (drag). If the fan freewheels, it's shot.
You mean the new fan clutch was nearly locked up all the time or are you talking about the old one? I found this post (the one at the top of the page) where the author states that MB designed the fan clutch to spin at half the engine speed up to about 90C at which temperature I suppose the clutch begins to go into a full couple.
http://www.peachparts.com/shopforum/showthread.php?t=121282&page=2

So I suppose even in "free-wheeling" mode, the fan isn't really supposed to free-wheel. Instead there should still be some drag to make it spin to some extent if I'm reading this correctly.

If anyone else has a new or fairly new fan clutch, I'd appreciate if you could do the same test that I did (spin the fan by hand with the engine hot and cold) and report your results here.
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  #5  
Old 08-05-2006, 03:12 PM
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Mine seems to freewheel most of the time, but with my new cooling system the temps never get above 86-87C even under full load (uphill...100+mph...95deg's out....) so who knows. I never hear any "fan roar" Our '83 has a plastic fan and it does roar on acceleration sometimes when its hot outside, but it also never gets above 82C on the gauge. Who knows.... I know mine's never gotten hot even with a "looser" fan clutch. When I spin it by hand hot or cold it has "moderate" resistance but not real strong. It goes maybe 2-3 rotations when I turn the engine off when its at operating temp.
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  #6  
Old 08-05-2006, 03:24 PM
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I've been curious about the same phenomenon. I checked the SD on the way back from CT at 100°F. ambient. Engine temperature climbed to 97°C. with no airflow (vehicle idling). Opened hood and shut engine down with stop lever. Fan stops instantly with engine.

I'll need to repeat this test at colder ambients to see if there is a noticeable difference.
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  #7  
Old 08-07-2006, 02:39 AM
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bump
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  #8  
Old 08-07-2006, 02:59 AM
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Similar to what others say, stops almost instantly when motor turns off.
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  #9  
Old 08-07-2006, 05:01 PM
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Quote:
If anyone else has a new or fairly new fan clutch, I'd appreciate if you could do the same test that I did (spin the fan by hand with the engine hot and cold) and report your results here.
I just replaced the fan clutch in my '98 a few weeks ago. I only hear the "roar" after about 10-15 minutes of full temperature operation (~80C). Once the car cools off, the roar will be back until the RPMs get up to ~2000 and then it goes away. I think this is normal operation for a properly functioning fan clutch.

I'll try some hand spins of the fan clutch tonight (both hot and cold) and let you know how it goes for me.
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  #10  
Old 08-07-2006, 11:33 PM
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Quote:
Originally Posted by DieselAddict
If anyone else has a new or fairly new fan clutch, I'd appreciate if you could do the same test that I did (spin the fan by hand with the engine hot and cold) and report your results here.
I replaced my fan clutch yesterday afternoon. Looked to be original, there was end play in the bearing and the fan spun at least five revolutions after the warm engine shut off. It was definitely contributing to why the engine ran hotter than normal. It also failed the "masking tape test" where with a warm engine, tape one piece of masking tape to a fan blade and to the shroud. Start the engine, if the tape doesn't break at idle, the clutch is bad.

The new clutch seems to spin about 3/4 revolution with a cold engine and stops immediately with a hot engine using the Brian Carlton test.
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Last edited by Brian Carlton; 08-07-2006 at 11:41 PM.
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  #11  
Old 08-08-2006, 12:08 AM
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Haven't tried it with a cold engine but when the engine is warm, the fan stops right with the engine. It runs at about 83 degrees C down the road, a needle-width more with the a/c on. More than five minutes idling at 95 degrees F + with the a/c on and it'll get to about 95 degrees C.
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  #12  
Old 08-08-2006, 08:58 AM
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Quote:
I'll try some hand spins of the fan clutch tonight (both hot and cold) and let you know how it goes for me.
I did the hot and cold fan spin tests and they feel exactly the same. I know my fan clutch is working properly as my coolant temperature never gets above 90C (sitting in grid lock traffic and 100F ambient temperature).
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  #13  
Old 08-08-2006, 09:11 AM
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The clutch resistance has nothing to do with ambient temperature. And it will never actually "lock up", there will always be a certain amount of play.

Engine temp will be well over 100deg before you notice any firm resistance.

Also the manual says to NEVER lay them down on their side. Don't know why but that's what it says.

Danny
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  #14  
Old 08-08-2006, 01:13 PM
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Thanks for all the responses. It does seem like my new fan clutch is fine, and it definitely makes a difference when it comes to keeping the engine cooler. Initially I wasn't used to hearing the fan spin when accelerating because I never heard that with the old worn-out clutch, but now I'm getting used to it.

dannym, I've heard that before about not laying the clutch on its side, but it doesn't make a lot of sense, especially when you consider that all the new clutches are shipped in mostly horizontal positions.
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