The long of it): For those of us that don’t know, (if any; I didn't) I think many do know there are 2 fan clutches, the ”regular” one and the “Tropical” clutch. I do have the tropical one on our brick.

Well, the last many weeks esp when the weather got real hot, the A/C just wasn’t up to par. I checked what I could, the belts mainly, but all seemed ok. I mentioned this to my mechanic, stating I would like to see if he could resolve this, even if it meant a new clutch, maybe a new thermostat, whatever it needs.

So I leave the brick with him. Several hours later I called and he said it's ready. He mentioned the fan and a/c are working fine now, that the main issue was that the clutch needed to have “grease” added to it. I say: “Grease??” what grease??”

Turns out the clutch has a grease in the assembly, sealed in, but seems those at the “factory” don’t take great care when building the clutch, leaving only a small amount of the grease in it causing the clutch to not work properly esp when its really needed a lot. I had no idea the clutch used any grease. There is some sort of "thing" on the clutch that is made just for putting grease into it if needed.

(I still have no idea how the grease functions to make the fan turn properly.) It’s a “special” type of grease designed for the clutch, some sort of synthetic stuff. So the bottom line now, things are “cool”. The temp gauge never shows hot, and the air actually gets colder than before!. (fingers crossed).

The short of it: If your brick is running hot with the a/c on, and the belts are OK and tightened properly, a good thermostat, check the grease in the fan clutch! The end. (finally)

Some people assumed that viscosity was engaging the fan clutch when warm. In fact it is the opposite, warm oil is less viscous at high temperature. It made no sense to me so I took one apart many years ago.

It was Aisin fan clutch and I wanted to see how it was made and operating.

What is engaging the clutch is the thermo-bimetal coil in front. It moves the center shaft just about 1/12th of a turn, say from 1 to 2 o'clock. That is enough to open the inside blade valve (that blocks two openings) and release the fluid that is acculated in the finned donut (you can see the shape if you look in front, it is around the thermo-coil). When fluid is released it floods the friction disk hense engaging the fan. Even when engaged the system slips a little. That motion pumps the fluid back in the donut. It will flow back in the friction disk area if the thermo-coil is hot, and that will keep the clutch engaged. If the rad sends cooler air at the front of the fan clutch, the thermo-coil will close the blade valve and retain the oil in the donut and that dis-engages the clutch. But there is still friction enough to turn the fan. But it can be stopped by hand. DO NOT DO THIS WITHOUT WEARING HEAVY LEATHER GLOVES.

If you live in area where road salt is used in winter I would suggest you use heavy grease and fill/cover the thermo-coil. That will prevent corrosion of the thermo-coil and also seisure of the shaft that is in the center of the thermo-coil.

I lived in Sacramento a ways back. My '81 242DL would over heat when stopped in traffic and the AC would stop cooling. I had done everything I could think of and so suspected the fan clutch. I tested it by strapping the fan to the pump bolts with tie wraps. It made no difference.

I installed an aux. fan in front of the radiator and that made a huge difference. Not satisfied as to why it needed the extra fan I tested the air flow pattern through the stock fan, at idle, with a strip of newspaper. The air appeared to be moving near the root of the fan blades only and then around the fan tips. Little or no air was being pulled through the radiator.

Since I could find nothing wrong with the fan or shroud I never understood why my car had this problem.

It is not grease but silicone oil.

I'm sure the so-called factory does a more than adequate job of manufacturing the part. Nothing lasts forever.

The "regular" clutch works the same way, Philip. It just doesn't kick in as quickly when it's hot. You really don't need a tropical clutch in the Bay Area.

The only renewed fan clutch I have ever dealt with was done by a previous owner's shop and it didn't last long.

I would keep my eye on the inside of the splash guard to see if any oil is escaping.

Better, I think, to just replace it.


--
'80 DL 2 door, '89 DL Wagon

Thanks for your input and correcting the word useage "grease"; Silicone oil is the right word; I stand corrected. We shall see just how long it lasts. I trust that Jon knows I would have just as well bought a new cluth if he felt that was the better way to go.

As far as Onkel Udo II's statement, I may have used the "wrong terminology" but I was not "blowing wind" as 'bulletproof' bears me out. The shop I go to is well known and has had the reputation of honesty for many years.

It's not just "silicone oil" but a special type that thickens with an increase in temperature. When cool, the oil is thin and not much torque is transmitted to the fan, so it isn't making a lot of noise and robbing engine power. (Of course, it's still spinning, so you can't tell by just looking and don't touch it!) When hot, the oil locks up and the fan turns full speed, moving lots of air. So why would the oil have leaked out of this "tropical fan"? I think because it was a different oil not intended for cold climates, when it would get really thin and tend to leak out.
--
1992 745, >500k km

I, um, ah, think he may have charged you to check the muffler bearings as well. Although what you describe is theoretically possible, I have never heard of this being done.

Here is a video that show what you clutch does:

https://www.youtube.com/watch?v=N_GkuTgJr3w

I would be more inclined to believe cleaned the radiator and coil. If you have a 1993 or retrofitted AC he might have gotten the secondary electric fan working again.

Now if you had told me the AC compressor clutch needed grease, I actually would had to look that one's operations up before getting so gosh darned skeptical, but adding grease to a viscous fan clutch really does sound like rotating the air in your tires.

All that said, I found a couple of you tube videos on how to change the fluid so I may be the one being to cynical.