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Radiator Fan Viscous Clutch Testing

13K views 29 replies 9 participants last post by  Kajtek1 
#1 ·
#2 · (Edited)
The test itself is easy. When you shut down engine with clutch engaged, you will not be able to push the blades with fingers.
Also when you observe the fan while shutting down the engine, the blades will stop immediately. When they make few turns with stopped engine, that easy to figure.
Some do "newspaper test" on running engine, but I would not recommend it.
Figuring out the point when the clutch should work is tricky part.
The thermo element is activated by heat coming from radiator, not the engine.
So just because your engine is hot after WOT for 20 seconds, doesn't mean clutch should engage, as radiator can be still cold at the "bottom"
Would you drive with engine > 105C for few minutes, that would be definite point.
Fact is that once the clutch engage you can really hear it too.
Infra red thermometer can become handy for this test.
 
#4 ·
Here is a good write up why the visco fan is there, and how to test it. This is for BMW but the same principles apply. As one does not drive the car with the hood open, thermal testing when the hood is open is not very meaningful. The engine compartment with the hood closed is how the thermal simulations were done in one of the videos I had seen from MB.

how to test a visco fan clutch - Pelican Parts Technical BBS
 
#5 ·
The Pelican test leaves lot to desire IMHO.
First it base the test on the fact that visco after long sitting locks the clutch and needs some turning before oil will flow and disengage.
Had only 1 BMW in my life and don't remember that, but I never heard the visco locking on cold Mercedes.
On my Ford Truck, the coming fan makes Jumbo-Jet style noise so I have no doubt when the clutch locks and when I start the truck after 2 weeks of sitting, the fan runs for about 30 seconds before it disengage.
Than sometimes it does not engage at all. Don't keep records, but have feeling the difference is between 60F cold morning and 80F noon engine starting.
Than they suggest following test while idling the engine.
Cold MB diesel will never reach 80C while idling, unless something is wrong with it, what is another story.
 
#10 ·
Both.. If the fan operates all the time at high speed you will hear it because it roars like a jet engine at high speeds. If it does not operate when it should, the fan will not turn as fast as it should, so the cooling, when needed, is ineffective.


With the replaced clutch, at stop and go traffic, the coolant temperature at the instrument panel stays in mid space between 80 and 100, and this is where I want to see. At highway speeds it is around 85 so the variation is minimal.
 
#11 ·
Different failures.
Clutch is free-wheeling on bearings and when I had bearing failure, it locked the clutch.
I was fortunate the bearing kept together as wobbling clutch would make a break in the trip.
More common failure is the seal leak and oil who powers the clutch leaking outside.
In this case usually you will see oily spot on the clutch.
Deplore didn't you report lately sudden drop in mpg?
That would explain higher engine temperatures. 300k is good time to check injectors.
 
#13 ·
Yeah, I had a look at it too prior, and the two types are speed and thermal plus speed activated. The one we have is only thermal activated. I looked at the version for the w210 but could not find anything yet. Please post if you find one. I looked at Sachs site but there is very little information. I guess you have to ask what you want to know then they may respond.
 
#14 ·
Well, I have not found any document that deals specifically with the W210 visco clutch. But the W126 document and other sites lead me to believe they are all pretty much the same.

Mine spins freely with the engine stopped. With the engine running you can easily stop the fan with a newspaper. So I think it is time for a new viscous clutch - no electric fans for me! Luckily the engine has not been overheating, probably because we don't have stop/go traffic and the car is mostly moving.

But... on my W126 380SEC I had the opposite problem - the clutch stuck. Got a new clutch for $30 and the whooshing is gone and torque is back.
 
#18 ·
I used what they call the universal tool and one of the wrenches (actually I was lucky, one of my friends had one in a red box for various wrenches and the fork tool).. The turn of the wrench is anticlockwise as you look at the from the front. 5 minute job, once you have the right tools.
 
#21 ·
Clutch is on order. I am leaving on trip tomorrow, so it will be a month before I get to it.

I should add that the electric fan in front of the radiator works correctly, but its belt-driven buddy did nothing. Opened it up to discover that at some point the drive belt fell off and was lying underneath. Popped it back on and now both work. So I was down to one fan out of three!
 
#22 ·
To close out this thread - I bought a cheap-ass clutch on Amazon (https://smile.amazon.com/gp/product/B00R3OMZ8Q/) and got a 36mm loaner wrench. Using a screwdriver to hold the mount, I was able to remove the old clutch and fan without too much trouble. Installed the new one and everything seems ok.

I went with the cheap replacement because my car is old, the part is not mission-critical and I want to experiment. If it craps out within a year I'll let you know.
 
#23 ·
This is the same one I got and installed two years ago, and it is still going strong. I check mine each time I raise the hood, and the last time was a month ago. The maximum coolant temp I had seen (climate control display) so far, is 92 degrees C, and it was on a Florida-hot day with stop/go traffic.

When this one eventually fails to operate properly, I still have the OEM clutch, and I will put some silicon oil in it to restore, and re-install it.
 
#24 ·
The dead easy test is the carrot test, get the engine to over 80c and it should chop up a carrot, if it stops this failed.

Do it on a nice summer day you can eat the carrot all ready chopped.
 
#25 ·
The 80C test will not do/
Viscous clutch is activated by radiator heat, what is not directly connected to engine heat and I think activation comes more at 85-90C.
You can have engine at 110C, at idle, but bottom of the radiator will be 60C.
Then when you let it idle on parking for few minutes and temperature will not drop below 110C, the clutch should engage.
Still best way is to check temperatures with infra-red thermometer as the same symptoms will come with bad water pump or closed thermostat.
 
#26 ·
Yes I should have said 90c and the thermostats operate at 87c and the visco cuts in at 3c over that.

In somewhere quiet you can hear the bi metal visco strip click as it cuts in, some say you can, mercedes say that you can.
 
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