SteveG

I searched the archives. Other posts are for clutch that is too loose. In my case, ('85 5-sp) hood up engine off, cold, the fan turns with a lot of resistance. It will turn w/o turning pulley against the belt. when engine started the fan is on at start. Analysis: Clutch engages fan at start: it thinks it is near whatever temp it needs to engage fan, I lose a couple hp turning fan that isn't needed and/or engine takes longer to warm and possibly runs a little cooler than it should. I guess I have to r&r the fan clutch and have seen notes on that adding Toyoto oil. (also, isn't the hood switch supposed to disable all fans when hood is up?) The hood switch is very loose in the mount, I can pop it out with light finger pressure, haven't checked continuity yet. The bulb is inop, but could be burned out. It's so small, I didn't think it would be of much help and I haven't even looked at the filament. A burned out bulb would'nt disable the switch? Any thoughts? TIA.

Paul D

Steve - The radiator fan clutch on the '85 is a fluid filled (some type of silicone I believe) viscous type coupling between the fan pulley and the radiator fan itself. There are no electronics used in this type of setup. The fan will always spin when the engine is running. I think the way it works (please somebody jump in if I'm out to lunch) is when the fluid in the viscous clutch is cooler there is more 'slip' in the clutch (less drag on crank) and when the clutch is hotter (engine at operating temp, radiator transferring hot air to clutch) the silicone becomes thicker making less 'slip' through the clutch (more drag on the crank). I was contemplating going to an aftermarket electric setup because it seemed to me that there would be much less drag on the crank converting to electric fan(s). I think it was going to be approx. $400.00 for the conversion vs. $18.00 for a silicone refill (no brainer for me, refill it was!). Hope this helps.

Erik - Denmark

Steve and Paul,
I just filled mine ventilator clutch.
Paul is correct when he said there is no electronic control - Pure hydro/mechanical
I do not know exactly how the clutch is working, but:
- Paul thinks the silicone oil get thicker when heated up, I don't think so, I think the viscosity of the silicone oil is (almost) constant
- There is an bimetal controlled valve in the ventilator clutch - I.e. regulating the resistance (Fan RPM) according to the temperature.
- The meaning with this clutch is to give a controlled slip between the engine RPM and ventilator RPM, not to use too much power on this cooling job - I.e. good ventilation with low engine RPM, but relatively low ventilator RPM with high engine RPM, where getting the cooling from driving speed.
- After I filled mine with two bottle of Toyota silicone oil I had a temperature drop - I.e. I got more resistance!
- The filling job is an easy and relaxing job - See <a href="http://members.rennlist/blueshark/page12.html" target="_blank">http://members.rennlist/blueshark/page12.html</a> - Here you get a good description how to do - There can be some change of the fixing of the bimetal strips according the model, but that's minor things - Only take care to mount it as it was before, i.e. mark it before removing.

Steve, when you turn the ventilator by hand (with not running engine) there must be some resistance, I think better to check by comparing with another 928

Maybe someone can explain the exact working principle of this clutch - That could be interesting to learn

SteveG

Erik, Thanks for that link to Dan Brindle here on Renn; don't know why that didn't come up in my search??
Anyway, it just seemed to me when cold the fan should turn freely and mine doesn't. I have observed other engines (not 928) with a similar set up. I don't know the mechanics of the non 928, but the non-928 fan turns freely, therefore doesnot engage at all when the engine is cold. I understand a fluid transfer provides for variable engagement with the crank, but mine is turning 1:1 on a stone cold start, OAT under 60F. I need to make it to some 928 gathering. "If it ain't broke, don't fix it" I have enough other things to work on.

Steve Cattaneo

When cold the fan will free wheel, if not the ball bearing on the shaft is sized or the disc valve is stuck open allowing supply oil into the working camber.

The viscous coupling operates similar to a torque converter; you have a supply chamber (silicon supply oil) and a working chamber (connected to the drive shaft). As the bimetal disc (control valve) heats up it opens the supply hole, allowing the flow of oil (silicon) from the supply chamber to the working chamber. Once there the silicon turns the fan drive disc, thus turning the fan the only connection between the fan and drive shaft is oil (silicon) just like a toque converter. The bimetal disc controls the oil flow.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Erik - Denmark

Steve,
Thank you for your excellent explanation - Then I also learnt some news today!
One comments, there is some resistance when cold, but not more than you can easily turn the propeller when holding the pulley and shaft - You can fell you have to turn the impeller in the viscous oil, and I think that's normal
I checked with my donor car and that's the same

Steve Cattaneo

Eric,
Free wheel is the wrong word, when cold the fan turns with some resistance.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Greg86andahalf

Steve G.,

My experience is this:

if the fan clutch is in good condition, the fan will only rotate 1/4 to 1/2 revolution when spun by hand on a cold engine. If it rotates much more than that, it is suspect. The toyota refil works great if done properly.

Greg