I notice it's using a lot of water (needs topping up every 150 miles or so. Coulda faultythermastat be causing that?

 

shouldn't use any water. A thermostat wouldn't cause water loss...

I'll let Adz confirm that one...

 

"Oh, another observation, the brass nut at the top of the radiator had no thread on bolt or hole, is this normal? It simply pushed in or pulled out".

No on else has commented on thisso I've probably misunderstood what you are saying.

But if you are referring to the cooling system bleed screw on the top of the radiator then something is wrong.

As per its name thisscrews into the opening in the radiator and has a sealing washer. If you have anon-threaded "plug"in this position thenI'd be very worried.It's probably leaking under pressure (as the engine warms up) and may alsobe preventing the engine from reaching operating temperature.

Cheers
JRH1946

 

This is a 1994 TDI. Lower rad temps and not hardly any pressure...

Not any diesels here in the US, so I left that one to Adz. He is familiar with them...