Update:
Refitted clutch and fan blade assay.
Engine RPM Fan Blade RPM
804 370
1100 490
1800 540
Had to suspend testing as the bi-metallic strip started to operate and my twins needed feeding
Anyhow, the clutch now seems to operate correctly. After a period of standing the fan resists movement, and at startup will 'whoosh' quite significantly. Then after 30 seconds or so will return back to normal running (quite, fan RPM about 1/2 engine RPM).
At a certain temperature (I think this is 95deg F according to several on the Tech Help forum) the clutch engages and the whooshing returns - wow, some serious air is being moved as the fan is rotating at nearly engine RPM - up until around 3000RPM where the clutch starts slipping again. This is by design.
So from these tests it seems like 30ml of 12,500CST was indeed a good choice of volume and viscosity. This fluid can be purchased in the UK from
R W Greeff. Min order 1KG @ 10UKP!!!
enough to refill everyone's bad clutch in the UK!!
However, I have one question which I hope someone can answer; my clutch doesn't seem to engage at higher RPM - say 2500, even though 95DegF has been reached. However as soon as the RPM reduces (around 1000) it engages and operates up to 3000RPM as it should. Is this correct? Maybe someone could test their known working MB clutch/fan for me (prefereably '89-'95) and let me know if theirs is similar.
Thanks