E300 Fan Clutch Failure

[Rick Miley]

The fan clutch on this car apparently leaked out all its fluid, and was freewheeling all summer. But I didn't worry about it because the car's cooling system is so good, and in fact it never even got over 100*C.

But a couple weeks ago the clutch locked up and stayed engaged all the time. I already had the part, but needed to order the special tools to get the center bolt out. Thanks gsxr, for your pictures of the tools.

Well, the picture below is what I wanted to share. This is the fan clutch after removal. This is exactly as it came out, and the cap was already off the bearing. Yikes!

[JimmyL]

If I might slightly hijack the thread, what is the purpose for a fan clutch? My fan is direct drive/no clutch. Texas climate.

[pberku]

From your picture, it looks like the fan clutch that you took out was not an original MB fan clutch, but rather an after-market one. Its strange that you would go through 2 fan clutches already on a 99 E300D

BTW, to answer JimmyL's question, the purpose of the fan clutch is to provide additional cooling to the radiator, especially in stop and go traffic under high ambient temperature conditions.

Phil

[JimmyL]

Help me here. If mine turns all the time, ie: direct drive, how does a clutched fan offer additional cooling?

[JimSmith]

Rick, How did the failure manifest? I had a few moments this summer where my temperatures would randomly creep up to 95 degrees C in traffic and while at highway speeds. I figured it was the thermostat, and bought another. And then the problem never happened again. So I still have the thermostat.

The fan clutch is a device from hell. The point is to reduce the energy expended running a fan at higher engine speeds when the car is moving through the air fast enough to force enough air through the radiator the fan is no longer needed. The power needed to run the fan is roughly in a cubic relationship with engine speed, so at twice the speed you need 8 times the power. To have the fan shut off most of the time at highway speed actuallly saves measurable fuel. So, since the fan is used to pull heat out of the engine coolant and into the air, it is controlled by engine coolant temperature one way or another. My 240D has none and I have never had a fan related failure. The 190E 2.3-16 has an electromagnetic one that gets its signal from a sensor measuring coolant temperature in the thermostat housing. I have yet to see this fail, although the sensor has failed twice in 230,000 miles. The one Rick showed I believe is a viscous coupled unit. It has a fluid reservoir that is sealed by a bimetallic "valve" that opens when the air from the radiator is hot enough to make the bimetallic feature warp. When the fluid is out of the reservoir it acts like a clutch between blades on a hub turned by the engine via the serpentine belt, and blades on the fan side of the housing. When things cool off the fluid somehow magically goes back into the reservoir and the fan free wheels. The viscous units have a hisotry of failures. Hope that helps. Jim

[pberku]

Basically the way it works is that when the air temperature in the vicinity of the fan clutch reaches 105C, the clutch locks-up, and the fan stops freewheeling.

The rest of the time the fan just freewheels and provides no cooling function at all.

Phil

[JimmyL]

Thank you for that info. That answer jogged my memory and was exactly what leathermang had told me. Give me a chance, and I will forget something....
That's why I print out so much of this stuff. I also right click and copy threads, and open a word document and paste the paragraph. Different documents for different areas of our cars.

[Rick Miley]

Jim, I first noticed it when the temperature climbed a little during the summer. As I said above, never over 100, but not the absolute rock steady 80 that it has always been. I checked it by opening the hood and watching it as I shut the engine down while the water temp was 100*C and ambient was 90*F. It kept spinning like crazy after the engine stopped, so I knew it was out of fluid.

There was also a nasty black gunk all over the fan blades which I assume was the fluid combined with dirt.

I could also spin it freely when the engine was dead cold, which you should not be able to do. The fluid settles in the bottom, and locks the hub when it has been sitting a while. Then on engine startup the centrifugal force distributes the fluid and it unlocks after a few seconds.

pberku - it is the original clutch that came from the factory. I've owned this car since brand spanking new. 109,000 miles on it now.

[gsxr]

Wow. That's definitely an atypical failure mode. Usually they just leak fluid and never couple. It's rare to see a bearing seizure, although I have seen worn bearings where the blade wobbles all over the place. Glad you got it fixed!

[83mercedes]

How could you tell if the fan clutch used in an 83 benz had failed? Would it keep spinning after engine shutoff?

[WANT '71 280SEL]

If the engine is hot (like over 105) and you shut the engine off, the fan should not spin more than a couple times after being shut off. If it keeps spinning (like my dad's 300E does) than you need a fan clutch.

Thanks
David