How many miles you have on the clock shouldn’t matter, if all cooling system components are in good working condition. Easy way to test the fan clutch is to see how much force it takes to stop it, with engine idling at normal operating temperature. Fold the newspaper and try to stop the fan with it, if you can with minimal force, then the clutch is toast. If you need to replace it, I would stick with top quality OE or OEM parts.

So called “heavy” or “severe” won’t be needed, (especially if you’re planning to install new radiator). All they will do is increase the noise level and likely lower engine operating temperature below desired level. Neither would be good, for your ears comfort but, also fuel economy, increased carbon deposit build-up etc.

I would also stay away from cheap aftermarket parts (Uro… or similar), they will likely be out of specs (either too slow or too fast) and probably not last very long. I once put one of those in my W124 turbo diesel and the noise was unbearable (even for diesel standards).

 

...I understand that when engine is hot, the fan should not move with your fingers as when trying to rotate it...

Hmmm... Not quite. When the engine is HOT and OFF and the fan clutch is ENGAGED it is difficult to turn the fan with your fingers. This is one way to confirm you have a working fan clutch. But this test has limitations. It can only confirm normal function of a working clutch. It cannot diagnose a faulty clutch because you wont be able to get a faulty clutch to engage properly.

[Edit: What I mean is it is not a 100% reliable method because some folks don’t get the engine hot enough or don’t wait long enough to allow the clutch to engage. Therefore potentially condemning a good clutch. Don’t forget also that with the hood open it takes a lot longer. So drop the hood, get the engine hot. Listen for the roar.]

The newspaper test with the engine running has similar limitations. There is no point in sticking a rolled up newspaper in the fan blades if the fan is not engaged and roaring. Consequently if your ears and eyes already tell you that the fan is not roaring at all even if you get the engine temperature up to 95 deg C, you have the answer. Bad clutch.

Probably the best test is to get the engine hot. When the fan starts to roar switch the engine off and spin the fan by hand. A good fan shouldn’t spin more than 3/4 of a turn. Just over one turn is acceptable. If it freewheels more than two turns the clutch is probably toast.

 

Appreciate the info. The only thing I notice roaring is when the auxiliary fans kicked in. Actually, I never heard the viscous fan roar.

 

Actually, I never heard the viscous fan roar.

It is a good sign, at least you know the fan does not follow the engine RPM fluctuation 1 to 1 but rather have a momentary lag... when not engaged.

However, even engaged a fan clutch holds only a certain amount and never fully. As far I am concerned, no fan clutch yields 1 to 1 against the pulley, or else they would use a flex fan or simply a fan, which is 1 to 1 with the pulley. By the way, many classic cars have flex fans and fans and if you noticed, they are not that noisy.

However, as robm.UK mentioned, it does not mean your clutch fan is up to spec just because the noise is not present. If you are doing work around there, better get a new one. By the way, if you are often in heavy traffic under hot temps, get one that engages at higher percentage (heavy duty). With a heavy-duty clutch fan, it will make more noise, but so little, it will not bother and or notice much difference against the old one. BTW, the SL's have small fans, so it is not that noisy no matter the RPM… unless that fan would be in a freaking S2000 engine like my son, ripping at 9000 RPM any fan would make noise…thank goodness he has electric fans and not a pulley fan. LOL

 

I added an edit in post #3. For clarification.

 

So I bought a Behr Hella OEM fan clutch and received it today. Ran the car all over town with AC on and temperature remain the same 90 degrees, however it's only 74 degrees here in CT. today. Soon the heat will rise and I'll see soon if the fan clutch replacement makes a difference. It does appear that the fan blade rotates faster.

 

Just to report as someone else here might have the same problems. A new fan clutch installed solved my high temperature problem and also with a new Aulixary Fan Resister, I believe helped as now I can see and hear the auxiliary fans working. Drove a couple hours around town in traffic today in 91 degree weather with AC on and No high temperatures, just around 92 degree at its highest point on the Cluster Temperature Indicator. Although when I stopped the car, as yet I haven't heard that Clutch Fan roar, perhaps the outdoor temps need to be higher.....

 

I have never heard viscous fan “roar” …someone may be confusing auxiliary fans kicking in at certain trigger points… with viscous fan clutch work.

Viscous fan clutch (in my experience with R129 and quite a few other MB models) has been smooth and gradual increase/decrease in RPM, based on temperature.

 

Hello, I’m ‘someone’. Can I help you? 😁

 

Can I buy you a pint? 🍺

 

I’ll have two quarts of ale please 😄

 

The viscous fan clutch on my ‘92 500SL is operated by a bimetallic strip, which as it warms up it expands. At a temperature of around 90 deg C the strip expands sufficiently to open an internal valve in the fan clutch. You can hear this valve open if you listen carefully. The valve is either fully open or fully closed. When open it releases silicone viscous fluid into the drive plates, which drives the fan. Before the valve opens the fan turns with little resistance at roughly 20% of the engine speed. When the valve opens, the fan very quickly picks up speed to roughly 80% of the engine rotational speed. If you’re stood in front of the engine looking over the fan with the hood open at this point you will hear the fan roar. You will feel warm air hit your face as the fan pulls a considerable volume of air through the radiator. This warm air hits the engine and is forced up and around the block, and its this strong waft (roaaarrrrr) of air 💨 that will blow the froth off your pint of beer, which might be wonderfully entertaining if you’ve already had a few.

 

Rob,
I believe my new viscous fan clutch has that "bimetallic strip" you mention as it's different than the Mercedes fan clutch that I removed and replaced. The new fan clutch does not rotate like on the backside of the old original fan did. Its just a different mechanism. I must say what a night and day difference in the engine temperature after I installed the new viscous van clutch.

 

Mercedes OEM viscous coupling part no. A 119 200 00 22 has a bimetallic strip. You can see it in the shot below -

The video in post #13 has a coil metallic strip. Not Mercedes.

 

In the pic above is exactly like my old fan clutch. When I removed my old fan clutch off the engine and onto the bench, I can rotate that strip 360 degrees. The new fan clutch, I cannot rotate the strip because the fins are in the way if you look closely. Just saying...

 

Yes, same with my spare Meyle viscous coupling. You can’t rotate the bimetallic strip. Incidentally my ‘new’ Meyle decided to leak silicone fluid while it was sat on my parts shelf for a couple of years. Won’t be fitting that now.
Did your new Behr Hella coupling come with a shorter bolt?

 

If there was a good way to add silicone in to the clutch.
It would last almost forever.
Also when the fan & clutch is out of the car, make sure that you park it vertical.
Regards,
aam.

 

Yes Rob, it came with the shorter bolt.

 

Yep, stored vertically like it said on box. Still leaked. Not a lot though. A few ml. But that’s enough to tell me it’s gonna leak if I fit it to the pulley hub. It shouldn’t leak.

AFAICT it’s leaking from the small diameter plunger underneath the bimetallic strip (flat rounded portion). So it’s the seal around the plunger. More it’s used, worse it will get. How long will it last? 12 months?

Judging by the commonality of this aftermarket design, I suspect Meyle is just re-boxing another make. The stick-on Meyle part no. maybe gives this away.

As a comparison between MB OEM clutch and Meyle? There is really no comparison. In my left hand the OEM is heavier, deeper and arguably [read: obviously] better built. The fin design on the OEM allows better air distribution round the clutch and also facilitates the attachment of the MB ventilated plastic protective cover on the front. I can’t see how it is possible to reattach this cover on the Meyle. In my right hand is the Meyle which looks and feels, well, lighter and cheaper, and notice the shrinkage cracks in the Meyle alloy casting just below the bimetallic strip in the above shot. As a consequence of all of the above it will stay in its box and will only come out when I am either desperate or in need of another chuckle

I noticed that the Meyle is not as deep as the MB OEM clutch. I am not sure if this also means that the fan will sit closer to the engine? If this is the case it would result in less shrouding around side of fan and a decrease in fan efficiency. Here is a shot of the Meyle. It’s 30mm from the mating face of the fan to the end of the shaft, and roughly 25 mm from mating face to rear edge of the fins. I don’t have the MB OEM to measure, its bolted up to the engine. Can someone check the measurements on an OEM clutch?

Here is the reverse side of the Meyle

Guess I don’t like the Meyle then.

I might cut this sucker open with a hacksaw...