| Mini 1 Diesel
Your symptoms do sound like mine (I'm the post above AKA Harry Worth ) - I don't believe the temp gauge - I think the water level drops below the sender so it doesn't read correctly but still sits midway. I'd being travelling down the motorway at a steady fifty when the gauge briefly moved up. When I stopped and put my hand on the rad. it was stone cold - I topped up with water and immediately the radiator came hot (presumably it was pretty much empty) and the gauge still remained at normal running temperature. My local one man band has diagnosed a head gasket - Bubbles of air and the water bottle is being pressurised even after briefly running the engine. I'm having the car towed to a more knowledgeable company so I'll keep you posted! | 
