a Fan Clutch
A fan clutch is supposed to be a fluid coupling device that allows the fan to rotate less than the engine speed. The fan clutch should engage before the engine gets up to 220°F. A standard cooling system fan clutch should spin at 33% of water pump speed (RPM) when not engaged and 75% of water pump RPM when engaged. A heavy duty cooling system fan clutch should spin at 33% of water pump speed (RPM) when not engaged and 90% of water pump RPM when engaged.
Unfortunately, a fan clutch can slowly empty its coupling oil overtime and often seizes. (the oil also can gel/thicken and grab). This means that it turns as fast as the engine! It results in:
false temp sensor readings (they are in the high velocity wind stream)
delayed thermostat opening (it is cooled too much as it is in the high velocity wind stream)
lots of noise
possible damage to water pump due to unbalanced fan and torque on the water pump shaft
Check for a seized fan clutch it by opening the hood with engine running in neutral.
Rev the engine and listen/watch fan. If you get a wind storm and windy sound from fan area then your fan is seized.
Click here for: Description of basic testing procedure
[B]There are three solutions: [/B]
1. Replace Fan Clutch with new one (~$70)
2. Recondition Fan Clutch (~$5-$15)
3. Remove fan clutch + fan and replace with 12V electric fan (~ $50-$200)
[B]Reconditioning is pretty easy. Here is what you need: [/B]
10mm, 12mm, 13mm wrenches
Thin blade Knife
Brake/TB/Carb Cleaner or other solvent
TOYOTA Silicone Oil refill the fan clutch*.
*The Toyota dealer says there are three types of viscous fan clutch silicone. They are rated at 3000 CST, 6000 CST, and 10,000 CST. (the higher the Cst rating, the higher the viscosity (THICKER fluid) All priced the same. The only reference to this stuff that the Toyota parts jock could find, was a TSB from 1975 specifying the fill procedure for the clutches of that year, The 3,000 Cst. was for all Toyotas except for the Celica (the only “sporty” car they offered in 1975), which got 6,000 Cst. The 10,000 Cst. was not assigned an application by the TSB. He guessed maybe the Land Cruiser but didn't really know. Anyway, the part numbers are 08816-03001, 08816-06001, and 08816-10001, respectively. (Each bottle is 18mL; you will probably need 2-3 bottles depending on your specific fan clutch)
[i][B]Note: [/B] Some folks have used 20/50wt. Motor Oil instead of Silicone Fan Clutch Fluid [/i]
[B]Here’s How to Do It:[/B] (There are links to web pages that have photo’s at the bottom of this article)
loosen alternator (13mm and 12mm bolts on mine)
remove four 10mm nuts holding fan assembly to water pump pulley
remove fan assembly
Remove four long 10mm bolts that hold fan to clutch (note the old oily dirt in center ring of plastic fan.
Wash fan in soapy water
Remove four short 10mm bolts from rear of fan clutch
Use knife to pry front and back halves apart (they are stuck together with suction)
Drain remaining "honey" oil inside
Remove O-ring and recondition with lacquer thinner
Clean/flush aluminum halves with brake cleaner or similar
Refill back half with Silicone Fan Clutch Fluid (or motor oil and a few cap-fulls of lacquer thinner)
[i]**My recommendation would be to use the Silicone fluid unless
cost/availability is a major issue[/i]
Reassemble. Installing the O-ring carefully and make sure to not pinch it between the halves of the unit
Check for leaks
Check for leaks and proper operation
Hope this helps you out.
This article was prepared using information gleaned from various sources including a post from ZmeFly, and material from http://www.pbase.com/bronte/fan_clutch, and several web forums pertaining to Toyota Land Cruisers and Porsche 928’s: