As above- can't see the problem though- rad isn't hot- if it's blocked would I still lose coolant? Any suggestions welcome.

So there is no coolant on the floor or engine bay?? What level is the engine oil. What colour is the exhaust fumes?

No coolant on floor or engine bay or floor- oil ok- no mayo- not checked exhaust- looks no different in mirror- what am I looking for?

head gasket leak ?

There's small hoses above the thermostat that run to each cylinder head that can leak only when its really hot and make like the water pump is finished since the water runs down the pump. However it stops quick when the engine is off and the pressure is gone in cold weather. Another favorite is the small hoses to the turbos at the rear of the engine - sometimes seen as steam and smell of anti freeze just after switch off. Radiator cap another loss point.

Good tip is to squeeze the top rad hose when the engine is well warmed up. Its should be firm (and hot). If its soft then you have a leak someplace.

Thanks for suggestions- turns out it's thermostat so hopefully no damage done!!