Dealer replaced the thermostat housing, said it had failed. Under warranty so no cost. Runs alot smoother now but I think thats down to the new sensor as well. The old sensor always gave funny readings, would climb and climb then drop right down.

Thanks for all your help. Im such an amateur.

Glad you've been able to get it all sorted!

Opps Ive just broke the thermostat housing! now I cant replace the thermostat! the bit where the tab goes into is broken off! Is this going to cause any harm to the car driving it?

I cant order one now till monday as everyone seems to be shut! is there a way I can bodge it?

Also the complete coolent system is covered in sludge could this have stoped the temp sensor?

I removed my, it is the one with the yellow O ring!

i had the same problem with my felicia temp gauge which had just had a new temp sensor fitted by the previous owner,with a blue collar on it but no joy needle still stuck at bottom of gauge. so i went to local dealer and found the fault is with the thermostat not sender. had to buy complete unit which cost