Ok, well it took me several hours as i'm merely an amateur DIY mechanic but i finally managed to change the viscous fan coupling, thermostat and stat housing.
The thing is that now, after being driven for only a few seconds (about 1000yds alls in all) the temp gauge is showing full temperature (needle in the middle of the guage).
There's no way it was up to temperature, and the viscous fan is just running at full engine speed, regardless of temperature.
I mean it's better because hey, at least the fan's actually cooling the engine but could the thermostat be stuck open or would it be a problem with the second hand viscous coupling i've installed?
A few pics as the therm housing was very different to the one i took off.
Thermostat is new. Came with the housing :/
Any ideas/suggestions appreciated.
DEVELOPMENT: Radiator is far beyond the reach of humble radweld, looking at getting it refurb'd on monday.
How do you diagnose, find and fix an airlock other than finding the heater not working and using the bleed screw at the top right of the rad?