That's strange you had any heating up issues. The 2005 X5 with 3.0 and a dead aux fan and new mechanical fan clutch on 95 to 99 degree days never did more than reach normal operating temps for me.

Same with my other bmws with the mechanical fan. The electric fan models swing pretty wide temp wise but the mechanicals are like tanks on the temp readings.

The only times that the temps have risen was when the mechanical fan clutches were warn or failing.

The mechanical fan clutch has a very short lifespan on bmw's for some reason. I think out of 50 or so other brands cars Ive owned only 2 had to have the fan clutch replaced. But all of my bmw's have failed on the mechanical fan clutch at one time or another. I wonder if they are undersized for the load or something.

Easy test on the bmw's is if the temp is 90 degrees or more outside and you sit at idle with the ac on for about 5 minutes and then take off it should sound like a jet plane engine if its working right :)

If the sound never gets loud on the fan after sitting in traffic or idling on a hot day for awhile and accelerating the fan clutch is toast even if it looks like its spinning normally. All of the ones I have replaced "looked" fine. But could be stopped fairly easily with a broom and would spin back to engine speed very slowly. A healthy fan clutch wont stop spinning when you touch it with the brooms bristles. A bad one stops easily.

I used some stiff foam to stop mine. It wasn't very difficult but it did spin right up to speed when I let it go. One could probably use a sliding scale to measure the force too set a baseline of what torque should be expected to know if the clutch failed weak. (Easy to tell if it failed locked when the blades shoot out through the hood the first time you doing a full throttle run)

So what you are saying is if I can stop the fan with my hands its possibly toast. It was about 45F outside, and the X5 was at operating temp.

Here is a article that I found on bimmerforums.com here is the link for that threat https://www.bimmerforums.com/forum/s...an-clutch-test


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 isn’t 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”.

written by MWrench
::: Welcome to MWRENCH

Nice details. I didn't know it was also temperature dependant I thought it was simply a viscous coupling like a clutch on automatic transmission. Very smart to have it lock up when getting warm since it's mechanically attached to the water pump the hub of course is basically the temp of the ECT once the thermostat opens.

The one mention I'll disagree with in the write up above is that the viscous clutch won't affect ability to get cabin heat as long as the thermostat closes.

Being able to get heat at -20°F without a problem is enough proof that no matter how fast the fan spins at say 20-30°F, you will have no problem getting cabin heat so cabin heat not a good "marker" to test the viscous clutch.. the temp sensitivity however makes perfect sense why it was so easy to stop when it was below freezing out.

The job of the bi-metal spring coil at the center of the fan clutch is to act as a thermostat and operate valving in the clutch as it sense the heat of air flowing from the radiator. If there is no bi-metal spring or it is not attached to valving(fake) then the fan clutch is likely only a viscous coupling. If enough viscous fluid leaks from either type of clutch it will effect performance. Trying to measure the stopped torque will not tell you anything as the clutch needs to be spinning for the valving to work.

Stopped torque meaning how much torque to hold the fan stopped when engine is running. At temp apparently matters.

The motor has to be fully warmed up to test the fan. Its supposed to slip more when not needed. The clutch can fail in two modes. If it locks up its mega noises like a jet engine all the time when the rpms rise. If its slipping (that's all I have ever had happen personally) it wont get noises on a very hot day when taking off and is easy to stop from spinning and doesn't spin back up very fast.

As short lived as the bmw clutches are it probably should be considered a maintenance item to be replaced on a regular interval but I have no idea what that interval should be.

All of the higher mileage bmw's I have bought needed that mechanical fan clutch replaced when I bought them.

The things are super cheap like $40 at autozone and not that hard to change. So if in doubt why not just replace it as a first step to cooling issues if you have never changed it before?

Great feedback I'll be testing out mine and wife's at earliest opportunity.


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Interesting read.