Hi I am new here after some advice before I spend money on parts. Have a 53 plate 2litre SType. The engine coolant low warning is nearly always constantly on. I was told probably sensor on header tank so thought j might just as well just replace complete header tank with sensor. However I made an observation Saturday that when travelling on motorway the warning us not present nor is the light. However as soon as off motorway. On normal round town roads the warning is permanently on. But when back in the motorway its permanently off again. Any body throw any light on this ????