I had a similiar problem...then one day it went into the red on a mountain road, I coasted to a halt when I could and the upper radiator connection to the radiator cracked. Replaced it, didn't help....so I replaced the water pump, it's all good. I believe that the original water pumps had plastic impellers, which have a limited life. You can purchase replacements that have metal impellers for around the same price. (Someone correct me if I'm wrong here)