First thing I'd do is replace the coolant temperature sender - these are very common on faliures. Under £20 for a new sender, and easy to fit > let the car cool down to cold, undo the coolant expansion tank cap, then simply a case of swapping out the sender. If you google it you'll find plenty of guides/pictures on Golf forums.

I had a feeling it could be the stat but why would the temp gauge intermittantly rise to about 70 degrees then fall away again? How would you go about blanking off 90% the radiator?

If it's the sender isn't that located on the other side of the engine just above the gearbox and wouldn't you have to drain the coolant before changing it?

I doubt the missing grill is the issue. It is a bit of a coincidence that the temp rose to 90 where it is supposed to be. However when these stats fail they open early. At the moment it does point to a faulty stat. How hot was the top hose when the temp indicated 90. Regards Peter

Edited by Peter D on 18/01/2012 at 08:34

This is really annoying now. A couple of days after fitting the lower grille the gauge started working intermittently again so I fitted the new stat which is a genuine part and all seemed fine. Then this afternoon after picking my wife up from work it stopped working again or I should say only going up a few degrees. When I got home I immediately popped the bonnet and checked the bottom hose which was cold. I take it from this that the new stat is failing or that something else is preventing it from opening (ie the housing)??? Any ideas anyone.