The Sapphs fan switch is in the rad which the fans are cooling regardless of the water circulating. Even my RST fan kicks in (uses a direct live battery feed) but switches off after about 10 mins of running and that fan switc is no where near the rad/fan..

I would think you have another issue else where John. I have seen a hell of a lot of issues around the Motorcraft thermostat recently and suffered a lot of hot running problems with my dad's car. We have now fitted a Halfords t/stat which was about £6 and the car is spot on...after we changed the head gasket due to the hot running problems as well!

The Halfords part number is HTK606....make sure it is stamped 82 degrees on it though.