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how to test a visco fan clutch

Fan Clutch test
First, lets discuss what the fan clutch does and why it is there. The fan clutch is just what the name says, it is a mechanism that will clutch the fan on and off depending on the need for more or less cooling air to flow thru the radiator. It is a thermostatically controlled device that when operating normally will vary the fan speed independently of the engine speed. When cruising down the road at freeway speeds, with outside temperature less then desert conditions, the fan should be merely be idling along, turning just fast enough to add a little air flow when needed, in this way the fan noise and drag on the engine is greatly reduced. When reducing speed, the fan clutch will sense higher temperatures thru the radiator and clutch up thereby increasing the fan speed to help maintain constant engine temperature. It may in fact, cycle as the temperature of the air thru the radiator changes depending on airflow. If the fan clutch operation is normal, when first starting the car, the fan clutch should clutch up and an increase in noise and airflow should be obvious. After about 60-90 seconds, the fan will un-clutch and the noise and airflow will drop. The fan will continue to turn but at a much reduced speed. As the engine warms and the thermostat opens to regulate the temperature, the air thru the radiator gets hotter and the clutch will sense this, thereby increasing the speed of the fan to maintain a normal operating temperature.
First signs of trouble:
A normal temperature indication at freeway speeds and an increasing temperature as the vehicle slows is one of the first indications of trouble. Many other things may give this indication but if the temperature seems to be stable at speeds but climbs in traffic or while stopped, this is a good indication that the fan clutch isnt working correctly. As the temperature continues to climb, the auxiliary electric fan should start but may not provide enough air to keep the engine from overheating.
Another sign of trouble is if the fan noise is high and never decreases after starting, and is there anytime the engine RPM is higher then idle, this means that the fan clutch is frozen and is not releasing. Although this will not result in immediately serious trouble, it will load the engine continually and gas MPG will be reduced. Load on the fan belt(s) will be higher and shorten the life of that component also.
Fan modifications:
It has been suggested that other models of BMW fans can be substituted to reduce the noise and load of the fan. This is NOT recommended! If the fan clutch is working properly, there should be no need to replace with a lesser fan. The noise and load of the fan should only be there when it is clutched up and the fan speed needed to keep that big V-12 cool. BMW designed it this way and it is never a good idea to alter the cooling system and in particular where alloy engines would be effected.
Testing the fan clutch:
If you have reason to suspect that the fan clutch is defective, here is the recommended procedure to verify the condition of the fan clutch.
1. Start the car (cold) with the hood open and note if the fan is turning, increase the engine RPM and note if the fan turns faster and the noise increases, if it does, first good indication, if it does not increase speed/noise, clutch is bad and needs to be replaced. (Remember, this must be tested after the car has been off for and extended period, over night etc.)
2. Leave engine running and note if the fan starts to slow down after 2-5 minutes, speed/noise should diminish and even raising the RPM, the fan should not make as much noise as when first starting, if it does slow, this is the second good indication. If speed/noise does not decrease, clutch may be frozen and should be replaced.
3. Leave the engine idle and watch the temperature indicator. When normal operating temperature has been reached, some increase in fan speed/noise should be noted, in particular when the RPM is increased. If temperature is fairly stable and the fan noise/speed increases or cycles, third good indication. If temperature indication continues to increase, with no increase in fan noise/speed, clutch is defective and should be replaced.
4. After the engine is at normal operating temperature or above, is the only time that the rolled up newspaper test that many people talk about should be performed! Take some newspaper and roll it up into a long narrow tube. Be carefull, keep hands and fingers away from the fan while performing this test! With the engine at full operating temperature and idling, take the rolled up paper and insert it on the back side of the fan and try to reach the hub of the fan avoiding the blades until close to the hub. Push the rolled paper at the fan increasing the friction to the hub area of the fan. If the fan can not be stopped easily this is the fourth good indication, if it can be stopped the clutch is defective and should be replaced. Again, this test can only be performed when the engine is at or above full operating temperature.
Testing can be performed in any order but just make sure the conditions during testing are those that are specified for that specific test.
Do not continue to operate the engine if the temperature continues to rise and certainly stop if the temperature approaches redline.

Author: Mwrench

in my opinion the best info how to test
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Old 11-23-2009, 11:10 PM
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The plastic fan blades become brittle as they age so make sure to wear eye protection and shield yourself when performing the rolled up paper test.
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Old 12-07-2009, 10:48 AM
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Possible further assistance...

Hi, I my viscous fan clutch acts normally, but it's fairly cold outside and I've just changed the thermostat and coolant so the cooling is working quite well, the temp doesn't go past the halfway mark...great! But is there anything I can do to do the last test on the Fan clutch (where it catches when it gets a little too hot...just over the halfway mark) until the weather warms up?...In June I'll be travelling in the south of france where it'll get pretty warm...just want to be prepared!

Thanks alot!
Old 01-11-2011, 07:30 AM
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Viscous Fan

On my '88 750il the temp needle always sat about one needle width to the right of center and if you go to Don Gale's website he has pictures of the temp gauge at various temperatures and mine was spot on at 195 F
Old 01-20-2011, 03:42 PM
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no problem at all with high temperatures for the car. Here in Japan we have in summer temperatures between =/- 40 degree C., that will be less in the siuth of France in summer, I have never had a problem here. But just make sure that the auxiliary fan runs well. The aux fan has 2 steps to run depending on the temperatures in the radiattor, here info on that
BMW E34 Aux Fan Resistor
and Don Gale website shows how to test the aux fan, link to Gale is on my website below
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Old 01-21-2011, 12:32 AM
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If it isn't broken but weak...There are methods to re-fill the viscous fan clutch...much less costly than replacing them, particularly in early models. The silicon fluid eventually needs to be re-filled into the centrifugal clutch hub...Toyota sells the fluid (others may as well)...search the site as well as e9coupe.com for the routine.

Jon
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Old 01-28-2011, 02:22 PM
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have done that, works even on my E32 Alpina B12 without any problem. As I am lazy I drilled a tiny hole into the oil chambers and filled the Toyota oil thru that inside and then sealed it with glue, already more than a year it runs without a problem.
Just wanted to test how it works, have a new visco clutch on stand by, but no need to install the new one
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Old 02-05-2011, 06:38 AM
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Ahh Brilliant guys!

Thanks for all the input!

I didn't get any alerts to the reply's on this thread, but I'll bookmark it for future updates!

I ran the can at idle for about 1/2 an hour while we were trying to put up tents in the dark (using the headlights for light), I don't make a habit of this as I know it's not reccomended, but the temp almost touched the red before I popped the bonet a bit to let more air in, then it was fine.

It sounds like I could do with trying the re-filling method!

Thanks alot for the tips!
Old 05-06-2011, 10:24 AM
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the refilling method
index

I tried that once,

t@JbvO̍\
Toyota silicone oil, part number 08816-03001

cut off visco fan clutch
Visco Fan Clutch (The real truth)
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Old 01-01-2012, 03:19 PM
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Still Not Sure Whether Fan is Working Properly

Have a 325i E46 sedan that we bought secondhand in 2007. Had about 50,000km when we bought it and has now done just over 200,000 km almost 10 years later. When I had it serviced about 3 months back at an independent shop, the guys said that the clutch fan was spinning too freely (when they rotated it by hand) for it to be working and it needed replacing and so I agreed to have it replaced.

However, ever since every time we start the car and first take off the clutch fan makes a loud whurring noise for maybe a minute or two and it sounds like I am driving a truck!! People in the street all turn their heads every time I take off from outside our house thinking that a big truck is coming down our (residential) street and all they see is me in my little old 3 series BMW!!

Is it really normal for the clutch fan to activate (substantially if not fully) for 1-2 minutes each time you start up the car and drive off? If this is true, then (1) the guys at the BMW dealership who sold us the car in 2007 (it was from their "Premium Selection"/2nd hand vehicles) must have known that the clutch fan was not working properly but they went ahead and sold it to us anyway, and (2) for the last approx 10 years/150,000 km the clutch fan has not been working properly but we have been driving the car totally oblivious to this without any apparent overheating problems.

Hoping that someone out there can help me out with this question.
Old 12-31-2016, 07:51 PM
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Is the noise only at Cold Start? If so, it is probably your secondary air pump which runs for about a minute to heat up the cats. It sounds like a hair drier and gets noisier with age. This air pump wont run on warm starts so it is only after the car has been sitting for hours.

The primary fan should not make that much noise at its loudest.
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Old 01-03-2017, 07:38 AM
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Quote:
Originally Posted by Jeron View Post
The plastic fan blades become brittle as they age....
Yes, that is true, here copied from an E32 problem, 1994 E32 740i:

Another odd ball issue...entire car vibrates
This issue just started to occur, when I first start my car it will vibrate the entire car, similar to a miss-fire yet it is not miss-firing and is firing on all 8, when I put it in drive and start driving it will vibrate like crazy then it is perfectly fine. It will do it on a cold start with 4 hours of sitting but subsequent starts after the issue has gone away does not bring it back.
-------------------
It could be a few things, but I will ask about the O2 sensors. When were they last changed? I had a sillier rough start issue, turned out it was my sensors. They were very new. I swapped to BOSCH and the problem was gone.
------------------
It has newer Bosch, they are a little less than a year old with about 7k miles on them.
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maybe either not enough fuel or too much. Try the following when the engine is cold and you have waited some hours> Switch ignition on, wait 2-3 seconds, switch off, switch on, this will start the pre-priming process for the fuel line/pump.
If that works, then your check valve on top of the fuel pump is defective and the fuel runs back into the tank till the pressure is gone in the lines between tank and fuel rail. BMW E34 Website: 535i hot start
Flooded: BMW E31 E38 E32 Starting A Flooded M60 840i 840ci 730i Or 740i
-----------------
Unfortunately that did not temporarily solve my issue If I very lightly rev the engine at idle the vibration is the worst, but not nearly as bad as when driving through it, at about 1K then is eliminated above that then reoccurs as it revs down. Just checked with Carsoft and the car has no faults. Stomp test didn't bring up any either. My buddy mentioned about it possibly being engine mounts, how would I know for sure?
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I doubt if it would be mounts, it would always be an issue.
--------------
Scratch that, I took a look again and I somehow lost a fan fin and did not damage anything thankfully. I don't know where or when that happened being I have not heard any noises of one breaking.
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Old 02-10-2018, 04:52 PM
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