OT: Radiator fan hydraulic clutches

Here's the situation. Have a BMW X5 where the electric auxiliary radiator fan is kaput. These are a real piece of work. BMW decided to put a variable speed fan with electronics that is controlled by the computer in one of the hottest, worst places. Like a regular one speed fan isn't good enough. So, they Cost $300+, fail quickly and are a bitch to replace. So, been driving the suv without it and it works fine, except there is no AC when you're not moving at all.
This got me thinking. Might the regular belt driven radiator fan clutch be bad? As I understand it, these have some kind of clutch based on a viscous liquid or something, so that when it's cold, the clutch loosens up and the fan doesn't spin at full speed. When it's hot the clutch tightens up and the fan runs at full speed.
Question is, how can you test that? With the engine hot after being driven awhile and with it 75F outside, with the engine off, I can spin the fan blade and there is a little resistance, but it moves pretty easily. I'm wondering if the clutch is kaput and that's why the AC won't work at all when not moving?
In other cars I've had, the aux radiator fan was only needed if it was extremely hot, like if I drove the car at highway speed, then parked it with the engine running and it was 90F outside. Then the aux fan would come on. But the aux fan wasn't needed for AC to work on say a 80F day with the car not moving.
Any thoughts? Like how do you know if the fan clutch is good or not?
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On Mon, 12 Aug 2013 22:41:22 +0000 (UTC), Red Green

restrain the blade when it is not running - start the engine and see how much force is exerted on the blade when cold - then repeat hot.
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On Mon, 12 Aug 2013 08:34:50 -0700 (PDT), " snipped-for-privacy@optonline.net"

You mean the air comes out the vent but it's hot, room temperature.

Don't know about BMW but on GM, it's easy to see if there's a clutch. It's something, as big as a desert plate, but when there were no clutches, there was just a litlle hub with screws holding it to the pully wheel.

I had a clutch on a GM car, 1973 or earlier, that failed and the fan wobbled noticeably. It wasn't just easy to turn but it moved front to back a half inch at the end of the blade. Of course I think it could fail without doing that.
Maybe you could stick a not-tightly rolled up newsppaper in the fan and see if it cut the paper to ribbons or if the the paper stopped the fan. I've never done this and it sounds stupid in a way, but you might learn something. Just be sure to let go if the fan is tugging the paper away from you. Mayb e you could attach a clip to a stick and put the paper in the clip.

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On Mon, 12 Aug 2013 08:34:50 -0700 (PDT), " snipped-for-privacy@optonline.net"

If you car is not overheating with the Aux fan broken I'd say the engine driven fan is fine. With that assumption it seems likely to me that the main, and possibly only reason there even is the aux fan is because the AC condenser simply doesn't get enough air thru it when the car isn't moving even if teh eng driven fan is working perfectly. If it did, why would they have bothered with the aux fan since, as you have discovered, the AC works fine when the car is moving, hence, the aux fan was put there to cover those times when it wasn't moving.
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wrote:

If that was my car, I'd probably put a stationary 12 volt fan in it, and run it right off the battery with a switch on the dash to shut it off when not needed. All this computerized garbage they put in newwer cars is nothing but trouble.
It's just like my pickup truck with ABS brakes. I had a brake line spring a leak. I replaced it, bled the brakes in the normal manner, and was 100% sure all the air was out. The brake pedal went right to the floor, but it did (sort of) stop the truck. I was told that these ABS brakes need a special computer and tools to "bleed the ABS unit", which costs over $2000. There is no way in hell that I'm gonna buy that, nor pay some shop a couple hundred to bleed my brakes. Particularly since I have never owned a vehicle with ABS and know how to use the brakes properly with my foot. I'm currently re-plumbing the brake lines to entirely remove the ABS. All I got to do is find a proportioning valve at the junk yard out of an older car, and it will be done, and I'll have normal brakes without all the hassle.
If I could find one with a good body and frame, I'd buy a vehicle made in the 1970's. No goddamn computers, no complicated and troublesome fuel injection, no ABS brakes, and plain old crank windows. I still have one 80's older car with a carburetor, and it still runs, is simple to work on, and always gets me where I want to go. It does have a computer for the ignition, but it's minimal. The surprising part is that it gets better gas mileage than one of the newer vehicles with comparible engine size, which has fuel injection and all that computerised shit. Unfortunately the body and frame are getting bad in that car, so it wont last much longer.
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On Tuesday, August 13, 2013 5:12:11 AM UTC-4, snipped-for-privacy@toolshed.com wrote:

I agree a basic one speed fan that's controlled by two temp sensors, one for the coolant, one for the AC would be my preference. But good luck trying to retrofit something into the form factor that you have to work with.
I also think this is probably due to the govt mileage mandates. Being able to run that fan at 1/4 speed at times will save a little bit of energy and if you do that in enough places it adds up. But the tradeoff is that not only is it more failure prone, it's much harder for a DIY fix. A regular fan, you give it 12V and if it doesn't spin, you know it's bad. With this BMW fan, it's not even clear what kind of signal exactly it gets. I would guess it's some kind of PWM signal, but who knows? Whatever it is, you're not going to have something available to make it run. The dealers computer can command it to run.

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On Tuesday, August 13, 2013 2:59:15 AM UTC-4, Ashton Crusher wrote:

In my experience with other cars, they bother with the aux fan for extreme conditions for either the AC or the car cooling. Like you've been driving 80 mph and then suddenly come to a dead stop in bumper to bumper traffic and it's 90F outside. They haven't been needed for the car cooling or the AC when it's 75F outside and the car is just idling. The engine fan is obviously moving enough air through the car radiator to keep the engine at normal temp. That air has to first move through the AC coils. So, I would think that it would be sufficient to provide AC. Again, I'm not expecting it to make the AC perform to it's fullest capacity. But it won't even blow any cool air without the car moving. With the car moving, it's OK.
And I checked the AC charge, it's fine.
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On Tue, 13 Aug 2013 04:14:44 -0700 (PDT), " snipped-for-privacy@optonline.net"

The problem you may eventually have, from what you are saying, is that when you are stopped and the ac stops cooling, the pressure in the AC system goes sky high and it's probably popping the high pressure safety switch and shutting down the compressor. Keep overloading the compressor like that and you will quite possibly have the seals blow out. I'd try to get some kind of $50 fan in there wired to run anytime the compressor is running.
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snipped-for-privacy@optonline.net wrote:

This may not help, and you probably already checked this, but here is what happened to me when I was having similar symptoms with my 2004 Hyundai Santa Fe overheating when idling and not moving in traffic.
I wasn't sure if the relays or whatever were working to send power to cause the fan to come on at the right temperature, or if the fan itself was defective. When I went to do the test, my plan was to unplug the connector that goes to the fan and then (when the radiator temperature started moving toward high) I was going to use a circuit test light to see if power was getting to the connector plug. But, when I unplugged the radiator connector plug, I saw that the pins inside the plug were damaged and that bad connection was causing the fan to not always come on when it was supposed to. All I had to do to fix the problem was adjust and fix the pins in the plug to make a better connection.
So, just to be sure, take apart the fan connector plug and make sure you don't have the same problem. Unlikely, I know, but I thought I'd mention it just in case.
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