Red blade cooling fans

[eriknetherlands]

Have purchased a bunch of fans for cheap. I needed only one, but got the rest for free.

I have little knowledge about them, have read a few posts on 9 fan blades and the viscous clutch, but still have some questions.

Wrt the blades:
Wondering what shape is original to e9?
Round tip end or square tip end?
5 blade original but 9 blade better?

Wrt the the thing (viscous clutch?) in middle:
Some are thicker then others, is there a different functionality?
Most of the 9 i can spin when I hold them by the large nut in the center, but I expected (incorrectly?) them to be locked. They do have frictional differences, some spin more freely then others. Free spin=dead clutch?
I've read that you can check by counting the degrees it spins when cutting the engine, but my engine has noting attached to it anymore....
Any insights are appreciated, Erik.

 

[Stevehose]

The red 5 blade is original. Red 9 blade never came on e9, the black ones came after the red ones ended. The 8 blade may be the "tropical" blade that was offered on e9?

A working fan clutch should spin when cold but engage when hot.

 

[HB Chris]

The viscous clutch was introduced on 74 model year coupes. RealOEM shows the nine blades with rounded ends for the 74, and these use the same water pump as the friction clutch. If yours has a large nut that is the spin-on version which requires a newer version of the water pump.

RealOEM.com - Online BMW Parts Catalog

BMW parts 2.5CS-3.0CSL 3.0CS Cooling system-fan/fan coupling

www.realoem.com

 

[deQuincey]

The red 5 blade is original. Red 9 blade never came on e9, the black ones came after the red ones ended. The 8 blade may be the "tropical" blade that was offered on e9?

A working fan clutch should spin when cold but engage when hot.

red 5, non equally spaced, is oriGinal, goes with a friction clutch
friction clutch is very radical, it can be stopped with your finger when cold, but it must engage strong when hot
the friction element is brake material, similar to hand brake, 2,7mm in thickness when new, once is used thickness decreases and finally the displacement of the heater element is not enough to engage it

mine is a viscous mounted 9 blade red fan
when cold it spins good and i will not try to stop with a finger, not even a newspaper, i will have bits flying around the
when hot and suddenly cut engine it will stop dead