I heart that it could be a problem to remove the visco-coupling with fan before changing the timing belt. As a result I didn't remove the fan before changing the timing belt, and it proved to be a challenge to exchange the timing belt in this situation.
Since I wanted to know what my visco coupling was like (there is a play of a few mils in the axial direction) I used the following trick to loosen the viscocoupling nut. As you mat know it has a righthand tread, so loosening has to be done against the clock direction.
- Put a 10 mm flat ringspanner on one of the fandrivepully bolts, making sure it is in roughly a 2 o'clock position.
- turn the engine anti clockwise by hand until the spanner runs against the crankshaft pully. The fandrive pully is now mechanically locked
- us a (adjustable) spanner to loosen the viscocouplingnut. As the fanpully is locked as the backside of the ringspanner is now tight against the nut, there is no torq force left on the fandrivepullyfixingbolt (I like the word!) self and as a result the viscocouplingnut can be loosened with a considerable torq. No slamming, just unscrewing. Mine was the first time in 3 years to be loosened and it seems the material is inoxidable.
If only I had known this in advance, I would have removed the fan before changing the timing belt. This worked fine for me, it may be a tip for you!
owning a 85 HP 2.5 liter double cabined 1999 mark 5 Turbodiesel and still liking it!