Hello, what is the function of the w124 fan clutch? I notice my radiator fan always run when the engine is on. Does it mean the fan clutch is faulty? thanks!

Somehow, the Fan Clutch senses the Ambient Air Heat Transfer Rate from the
Radiator and ENGAGES, causing MORE Air Flow across the Condenser/Radiator
interface.

(As the air flow from the Radiator HEATS UP, the Clutch engages Increasing the Heat transfer rate of the Radiator.)

[It's a Bi-Metallic Strip that functions as the "Engagement".]

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'84 300SD sold
124.128

Unless the motor is off, you'll never see the fan not turning.

What's important is whether the engine is driving it or whether it's turning simply from vibrations or friction or the minimal coupling remaining.

The "function" is fuel economy.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

I just discovered there is two types of fan clutch on W124 - my '88 230TE has an 'electro-mechanical' fan, which freewheels until heat sensor hits about 100C, then tries to take off (you can hold it with a carrot ticking over - not when its driving tho!!), but my '93 300TD has 'viscous' clutch which is push rather than spin at rest but spins up when the engine runs and seems to be blowing quite hard all the time. This type has a 'fluid coupling' some kind of 'silicon oil' - if this leaks the clutch won't drive the fan

- at least thats my current understanding!

Function? maybe to reduce shock loading on the fan? the electric one prevents overcooling by not driving til the temp is high enough I suppose

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cheers!!

We only got 5 and 6 cylinder W124s in the US so they were all viscous over here. The electric clutch was specific to the M102 engine. My 190e 2.3 used one. I better design in my opinion.

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CENSORED due to not family friendly words

Ah that explains some confusion! 2.3 is a sweet little engine - and yes I think the electric fanis much more sensible

cheers!

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cheers!!

So if the engine runs a little hot (temperature gage at 100celsius) during city driving, can one assume the fan clutch could be failing?

I notice the engine compartment is real hot one day when I tied to check the transmission fluids and the stick was so hot I can't even pick it up without wearing gloves.

Yes. You need to do testing.

My 300sel never gets that hot.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

This is not hot enough for the aux fan to run, is within spec. Stop and go driving in hot weather will often get the temperature high enough to run the aux fan.

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Gone to the dark side

- Jeff

Are you kidding??

"Sorry, I was going by memory. Every 400E I have ever seen has only had an electric fan, including my neighbors. However, I have yet to lay eyes on a E420 or E500, I have no interest in gasoline V8's. I do recall there being an incredible amount of space where the fan and shroud would be...
______"

THere is absolutely less room on a M119 than anything but a M120!!! All the cars have a electric fan on the front for a/c cooling... They all rely on the fan clutch.

My 86' doesn't have any cooling problems- I don't know why ppl call the problematic. It did have a radiator replaced about 5 years ago due to aging plastic and a new water pump at 70,000 miles. The new fan clutch it easily holds 85-90c in 100-105 weather. Only pops up a few degrees in stop and go, but never hits 100F. Before it would creep up and it wouldn't cool back down quickly. I'm hoping that replacing the fan clutch and improving cooling will only help delay headgasket failures.

86's would still have asbestos in the gaskets ... so maybe they are a bit stronger than the later re-designs.

Michael

the purpose of the fan clutch (aside from cooling) is to prevent the fan from coming apart at higher rpms.....

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1993 300E, 2.8 M104 .....

Start the engine, the clutch is engaged. It fairly quickly disengages when the fluid re-distributes, and unless the air across it is hot enough, stays disengaged and only transfers miinimal power to spin the fan through friction.

If the radiator air is hot enough, the clutch will re-engage to cool the radiator, but it will also limit the max. RPM of the fan so that it does not come apart and do a BMW through the hood thing.

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Gone to the dark side

- Jeff

I think everyone has great ideas of what it does...

But why a fan clutch is more simple: Saves fuel. Running ala old american iron a fan all the time drains fuel and slows the engine heating up contributing to wear.
It's not uncommon to see an electric fan on all the time or nearly so in the summer- your running the a/c.

A large electric fan at the time these were built wasn't a cost effective option. Puller fans are more efficent than pushers if I remember correctly. With a clutch you can have a 10 -15 hp fan only when you need it.


M

Electric fan is more efficient and more reliable. It either works or it doesn't. Most of the overheating problems on these cars are caused by the viscous clutch fan that still has some friction but not enough to keep the car cool. There is really no perfect way to gauge whether the clutch is good or not. The fan itself is way too small to have any chance of keeping the M103 under 100c in hot weather or stop and go traffic with AC on. Add a little bit of wear to the clutch and you'll slowly work your way to a new headgasket.

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CENSORED due to not family friendly words

124 cooling systems, as they age, become problematic. It could be any one of the components, if not a combination of two or more. When you first start your car cold, you should hear the fan roar as if pulling air, then it should subside as the engine warms up. Then, as the engine goes beyond the the prescribed temp, you should be able to hear it pulling air once again. Also, your aux. fan should engage at some point as well, and anytime the AC is used. I would also think about replacing the water pump if it hasn't been done at some point. Also bear in mind that a head gasket can cause overheating without any other noticeable symptoms, a hydrocarbon sniffer can rule this out.

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1987 300TD Turbo 5-spd
1991 350 SD Turbo (Frankenstein 603.970 crank, rods and head on a .50 bored 603.963 block )
1982 300D euro 617.951, 4-spd
2003 E500

2000 GMC C2500 6.5 TD (Double ott, ex DOT truck)
1980 Scout Traveller SD33T (Resting!)
1997 GMC K2500 Burban 6.5 TD (mid engine rebuild)