Have now drained, flushed and refilled the cooling system but the above problem still exists. Here's some more detail (sounds very much like the recent problem with the pinto Sierra a few posts back):
Start the car up and it eventually starts to get warm. By this I mean that the heater feed pipe and the radiator top hose both get warm (not hot, just warm), however the radiator core itself doesn't get warm - the gauge is now starting to move and settles just on the bottom of the white scale (about a quarter) after a few minutes idling.
If I leave the engine idling the gauge doesn't seem to move much above the beginning of the scale, though if I hold the engine at about 2000rpm it slowly climbs to about the half-way mark (which is where I'd expect it be) and goes no further. The fans also do not run. If I take the car for a steady run (50-60mph single carriageway A roads), the gauge slowly goes down, sometimes off the bottom of the white scale altogether! Stopping and lifting the bonnet when this is case, the rad top hose is only lukewarm, as is the radiator core and output from the heater.
Tonight I put a big bit of cardboard in front of the radiator (had to remove the top mountings to do it) which covers the entire core and intercooler, though there is about an inch gap between the card and the radiator. Driving home 'energetically' I expected the gauge to climb over the half-way mark but it just sat there, again, even with the car stationary and the engine revving. Fans still don't run, but do if you disconnect one of the radiator switches and short the wires together.
I took the thermostat unit off this morning and held it under the cold tap - it was firmly shut, though I wasn't able to check what temperature it opens at.
Any ideas? It's sounding like a thermostat opening far too early (not replaceable on it's own, it's part of the plastic cylinder housing), or maybe the cooling system is plumbed in backwards???!
Darren