Way to deliberatley lock fan clutch - 1987 300SDL ?????

I have replaced the fan clutch assembly on my '87 300sdl a couple of times and I really don't think that this clutch is a good design. If your mercedes is overheating or running warm at idle, then probably the
oil filled clutch is not working right.
My question : Is there a way to 'lock' the clutch so that the fan is always engaged? I want to do this to my non-working clutch, not to a brand new one. I know of a fix for the bimetallic spring for a new clutch assembly, but I'm not interested in that one. I want to lock my old one.
Any ideas?
Thanks
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VERY VERY rare for the fan clutch on a Mercedes to go bad! 99 times out of 100, it is the radiator that is the problem. When you engine is running hot and the fan clutch is free wheeling, feel the radiator in the center directly away from the hub. It will probably be cold. Poor flow thru the radiator keeps the clutch from locking. It is a good system if every thing is working correctly.
I am a tech/shop foreman at a MB ONLY dealership and in the past 27 years, I have only seen ONE bad fan clutch. All the other so-called bad clutches were fine after we replaced the radiator.

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I agree... very rare for fan clutch to go bad. Other than radiator... the temperature gauge do go bad and thereby reading high temp when in fact is not.
You really need a touchless infrared temperature gauge... I just got one and it registered my car car in normal operating range of 80 when my instrument cluster reads 95 degree. I pointed that thing at the brass fitting of the temperature sensor.
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On various Mercedes forums there is quite a bit of discussion RE the fan clutch. There are instructions how to refill the assembly with a very thick oil (available from Toyota dealer). There are quite a few folks who seem to have problems with the fan clutch.
If the clutch is stored in a horizontal position the oil will leak out (had one of those- the oil will be all over the unit in the box).
A local repair shop who specializes in older MB seems to think that the viscous-fluid clutch fans are not reliable and think that the fan clutch failure often leads to overheating/cracked heads. They do like the electrically activated fans on some of the MB's.
My fan will 'free wheel' even when the engine is very warm. If the fan is working correctly then it only activates (locks) when the engines is really really hot.
I also agree that the temp gauges are not reliable.
Bear in mind that reliablility is relative. I have two MB's, one a commercial truck with over 1 million miles (never had the engine down, never replaced the clutch, never even replaced a u-joint). My 300sdl has 325,000 miles on it and has had only routine maintenance. Most cars would have been crushed long ago lol. I just want to preserve the engine and would gladly sacrifice a mpg on the car to have the security of KNOWING that my fan clutch is cooling the engine.
Thanks ...
I am sure that it is true that the radiator is not working at 100% of designed effeciency in most cases. I am sure that mine is not. A new radiator is approx. $400, a new fan clutch (with plastic fan) is approx. $250.
Karl wrote:

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If I may say a word on the topic: I own MB C200 Elegance 1996 and only after 145000 km I had to replace fan clutch,. The old one simply gave up and even very hot radiator wasn't able to make it work. Visco simply wore out. After the temperature rose a few times to 120"Celsius I replaced it to new one (not geniune orignal, but sitll very good - Hans Pries Topran). New one works good and engine never reaches more than 95"Celsius. I asked my mechanician about changing only oil and visco in old clutch, but he said, that it is very delicate matter, there are very few people, if any, who can make it right, and even so, regenerated clutches seem to fail much sooner, than new replaced. So if you have the clutch regenerated, maybe it failed so soon because people that vere doing it simply didnt do it good enough. Besides - new clutches make no problem with storing in vertical or horizontal position, as old ones were. So if you can, replace it, and make sure they'll fiot NEW one, not regenerated or "good" one pulled out from an old car. About locking the clutch - if you want to do it the hard, "hammer" way, three good, durable screws and drilling machine will do the job. Three years ago i was on the vacation in Croatia (I'm form Poland) and our visco broke there. One mechanician fixed it mentioned way..... Well, we made way home without any problems, but engine rumbling a litte more after exceeding 120 km/h. That way it will always cool with maximal power, and engine will sound more sporty, but you have to remember, that it also will take out a few horsepower. One more - you'll newer have to worry about changing clutch again :) Btw, idea of checking radiator is a good one, as it may be the cause of problem. Also check cooling liquid pump for correct working and thermostat, as if it is broken, it can also make problems. Well, that's it..... Andrzej

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