purpose of w124 fan clutch?
 

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!

Magically
 

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".]

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.

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

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

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.

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.

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.
http://img.photobucket.com/albums/v2...g?t=1279818818

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

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.

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.

BTW, when MB stuffed the 119 V8 in the 124 they went full electric, I wonder why?

Check your data. No they didn't.