A few years ago I had a bad fan clutch, so I did some exploratory surgery on it:

The fan clutch uses a silicon oil viscous fluid in two chambers inside.

A Bi-metal strip on the front bends outward as it warms and opens the valve from the reservoir side to the clutch side.

Centripetal force provides the pumping action to move the fluid.

When it sits for a few hours, it will spin the fan briefly on startup, then freewheel.

After 100,000 miles the bearing seals inside wear, and the bearing lube starts to weaken the clutch fluid's grip.



Both the S4 & S5 clutch freewheel when cold.

The s4 clutch increases it's bite gradually with temperature rise.

The s5 clutch is more on-off. (It just coasts until is gets warm)

Once they are warm, the fan speed goes up with engine speed to about 4000 RPM.



As the engine revs higher the fan stays at ~4K.



THE SIMPLE TEST:

If your warmed up fan only revs up to < 2500 RPM, it's worn out.

 

Why is it that I can buy one of these things for my Chevy truck at any auto parts store for 30 bucks, but one for the RX-7 cost like $190?

 

maybe see if you can get a flex fan that will fit

 

I would rather run a flex fan than the e-fan, does anyone know how much the waterpump pulley is underdriven? Most flex fans have a 10,000 rpm limit, I'm sure the pulley isn't 1:1, I remember someone saying 60:1, does that sound right?

 

fan clutch should have some resistants in it spin it w/ car off, of course

 

[quote name='1988RedT2' date='Jul 1 2005, 03:20 PM']Why is it that I can buy one of these things for my Chevy truck at any auto parts store for 30 bucks, but one for the RX-7 cost like $190?


[/quote]



The cheap one is a mechanical friction clutch, so the warmed up fan runs at full engine RPM.

The 13B fan pulley is about 1:1, maybe 1.1:1



The Mazda fan clutch is a torque converter type design to give more pull at low speeds & maintain about 4K RPM as the engine revs higher.



That don't come cheap..



A flex fan (with enough pitch) mounted to a mechanical clutch would make a fair substitute.

 

well i checked my fan clutch the stupid way, my car is overheating driving around town when i get on the highway it the temp goes down to where it should be.i let my car overheat a little opend the hood and stuck a tube in there and it stopped with very little resistance.so i just orderd a new fan clutch from british victoria today total was $172.00 with shipping i will post my results when i recieve it in about 5 or 7 days .all the mazda dealers i called wanted about $245.00 for this part .i dont know if the 1 i am getting is oem or some aftermarket 1. i was unable to find aftermarket one on my searches but as long as it works ill be happy.

 

The aftermarket one I put on my 87 fit the S4 but worked like the S5.

It freewheeled until it got warm, then it hooked up.