I've got a 130TDI QS

My temperature gauge won't get to 90, it will manage about 85, then drops slowly to about 70, then goes up and down slowly in that range.

I initially thought it was just the coolant temp sensor, so have ordered one - waiting to fit - need the engine to be stone cold (incidentally, my car uses the 2pin petrol coolant sensor, not the diesel 4pin one?!)

I still have heating in the car, but describing the temp needle behaviour to a fellow car geek, he reckons it could be the thermostat.

Anyone with any thoughts?