Originally Posted by simmo300e

The fan closest to the engine - running off the belt instead of electric - has a visco clutch which only kicks in to high gear at 2000 rpm.

If you want to check it's working, edge a rolled towel or cloth into the blades while its running and see if it stops. if it stops, the fan clutch is shot.

The important points to note here are 'edge' and 'rolled towel'

Other than that, you might want to check that the cooling system does not have an air pocket in the cylinder head. this will cause the symptoms you describe. the bleed hole is a fiddly bolt in the cylinder head, between the sensors towards the front of the engine.

Re your oil pressure, that's not right. should peg at 3 when the engine is running above idle, 1.5 to 2 at idle. I've read that using the wrong (read cheap) oil filter can cause this behaviour.