Replaced my faulty thermostat yesterday. I was sure it was stuck open as the car would reach 90 degrees, but it took about 15 mins of town driving, at it wouldn't reach above 70 degrees on the motorway. Simple enough task. Car now reaches 90 degrees within 5 mins, despite the very cold air temperature, and of course the engine oil heats more quickly now too, resulting in less engine wear caused by driving on a cold engine. Very happy that another simple fix has made a big improvement to the general running of the car.......I wonder what'll need fixing next??