while driving on the interstate 70mph or so started loosing power temp gauge in low end of scale. pulled over and radiator overflow was spitting out coolant. I have the fan wired so that it is on most of the time and it is working. Have tested the thermastat, temp sensor, fan sensor and radiator.(all OK) motor must be pulled to replace the water pump but I can feel the pump fins turning when the engine turns over. Tested the cylinder compression both at 170lbs. no pressure comming out the radiator when engine is running.so no breach of head gasket indicated. Anyone have any suggestions?