Well, so far I have replaced the t/stat, all hoses, water pump,viscous fan clutch, beltand now radiator. I had to drive the rover home about 250 miles from the Mountains of upstate New York back to Long Island. We left late at nght and went about thirty miles before the temp started to raise again( about 70 75 mph) (rpm about 2750) It would go about 15 minutes and I would pull over and refill with water( about a gallon each time) I stopped and removed the grille and hard wired the a/c fan to the battery to run continously,this went on for 5 to 6 hours. Totaling about 75 to 80 miles.(carefull not ot overheat, mind you, never in red longer than 30 seconds). At the last stop I refilled coolant and tried to stay about 1875 to 2000 rpm. This seemed to work. We never went past a smidge over half on the guage.( never before over half) This technique managed to get us home without furthe incident. It did however boil over when I pulled into the driveway........So this brings me to my question!..........my diagnoses were as follows( my first Rover so please let me know if logic is correct)........There seems to be no coolant into oil at all, and I ran truck with cap off and did not notice any bubbling ( a sign of air from combustion chambers leaking into cooling system and causing overpressurization)So all of this being said....the coolant is boiling and over pressurizing system, thus overflowing and causing coolant loss......Is this overpressurizing the symptom or the cause ( bad head gasket)? Or could all of this headache be caused by something as simple as an automatic belt tensioner. It is my last hope before testing cylinder compression and all that jazz......Is this part capable of failing causing the water pump not to turnunder load as fast as it should, thus not circulating coolant fast enough through radiator to dissapated heat, and also not allowing fan to turn fast enough to draw cool air through radiator? Please if any one could help I would be very grateful//////Thank you for your time/////

 

Pressure test the cooling system. You may be able to detect the leak this way.