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  #1  
Old 06-20-2007, 08:38 AM
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How to check fan clutch

I have been going through my cooling system on my 83 300sd to try and address some mild overheating (100C+ on hot days). So far I have replaced the thermostat and waterpump, flushed the entire system including the block and replced the sending unit. All the above have helped. Yesterday w/ ambient temps in the low 80sF the engine runs @ 80-85C on the highway w/AC on. I am concerned that on hotter days it still may run a bit hot. How do I check the fan clutch. With the engine off shouldn't the blade spin freely? Mine has a bit of a drag to it when I try to spin it by hand. I don't remember if the motor was warm when I checked it. Otherwise it seems OK. Not loose etc. Not evidence of leaking fluid or a bad bearing.

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Old 06-20-2007, 09:12 AM
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Check out the thread that says Best Fix Yet, I just listed a bunch of threads that will get you through this.

When you stop your engine the fan should only turn one or two revolutions, if not then you might need to add some fluid.
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Old 06-20-2007, 10:15 AM
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I think mine is not loose enough. It takes some effort to get it to spin- it won't spin freely. Does that mean it is pulling in too much air? Or maybe not locking up enough when it is hot?
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Old 06-20-2007, 01:05 PM
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There is viscous drag, it will not spin freely.

About 105C the fan should be engaged, rev the engine and you should hear the fan rev with it. It will not spin full-speed with the engine, is designed to self-limit.
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Old 06-20-2007, 05:57 PM
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Quote:
Originally Posted by Paulc66t View Post
I am concerned that on hotter days it still may run a bit hot.
I have found that the engine temperature is far more sensitive to load than ambient temperature.

If you take it up a decent hill on the highway, requiring close to maximum continuous power, and the engine remains below 105C., you've got nothing to worry about.

You might verify that the electric fan is working properly. It won't start unless the engine reaches 105C. (a/c functions excluded).

Although you may be concerned with higher ambient temperatures, you'll find that it's typically not an issue unless you're under a very heavy and extended load.
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Old 06-20-2007, 07:27 PM
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Well, as soon as you start the car, while it is still cool...Just stick your hand down there, grab and attempt to hold the fan still.

If you are successful, it is working, if not..., Collect up your fingers from the fan shroud, and head for the E.R...
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Old 06-20-2007, 08:17 PM
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Simple. When the car is hot, shove a carrot in the blades. Chopped carrot = good enough. Scuffed carrot = new fan.
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Old 06-20-2007, 09:15 PM
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Drag on fan sounds normal. Just checked my SD, cold. The temp in my CD runs higher than the SD, not 95c, though.
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Old 06-21-2007, 01:48 AM
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Originally Posted by toomany MBZ View Post
Drag on fan sounds normal. Just checked my SD, cold. The temp in my CD runs higher than the SD, not 95c, though.
Did you do the "Grab-test", I suggested..?

I'm assuming you didn't, because you are still typing...
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Old 06-21-2007, 02:10 AM
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Originally Posted by truckinik View Post
Did you do the "Grab-test", I suggested..?

I'm assuming you didn't, because you are still typing...
LOL No, checked while not running!
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Old 06-21-2007, 07:11 AM
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I'm thinking that my v clutch is bad too, it seems to spin the same (by hand) whether its cold or I just shut it off @ 95 C.

It gets very hot when idling and runs a bit cooler (but still too hot)

I'm gonna put 2 electric puller fans in there instead.
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  #12  
Old 06-21-2007, 11:00 AM
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The fan will normally spin freely, whether the car is hot or cold, if it is not actually running. If you start the car up, when the engine is already hot, the fan will engage immediately, if it's cold, it will engage when the car gets hot.

So even with the car being hot, the fan will spin freely, if it is not running.
You will not be able to tell if it's working or not, unless the car is actually running...

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