Nissan Patrol GQ - Heating Issues - I can't find the cause.

[the evil twin]

snip...
I am not sure how a clutch fan works, perhaps it needs to get hot first ( to make it engage ? )

Yes they do indeed need to be hot to fully engage.

For the first few seconds from cold on initial start up and when hot they should shift an immense amount of air.

If you stop the engine from hot the fan should stop immediately, if cool to normal it should freewheel a teensy bit, max of couple of revs.
If it freewheels too much the clutch is shot