So I have a 2011 Xterra, 150,000 miles. It has been the best vehicle for the last five year but all of a sudden my temperature gauge started rising until it reached that notch before over heating. I have changed the thermostat, temperature gauge, heater core hose, heater core hose assembly, the tensioner, serpentine belt, water pump, timing belt tensioner, and finally the radiator. I have essentially put an entirely new coolant system in the car and it is still having the same problem! The temperature rises after reaching 60 mph and over, then it continues to fluctuate the entire drive. If anyone has any more ideas they would be much appreciated.