I had the head gasket, the thermostat, thermostat housing and the upper radiator hose replaced due to coolant loss and smoking exhaust. Now my question is that when I run the engine for about 10-15 minutes ( driving around not idling ), the upper radiator hose gets very hot and very hard. The heat works ok, and there is no smoke out the tailpipe and there are no bubbling in the radiator ( when Idling ) and I have no coolant loss. I tried running the car without a thermostat and it has the same problem. The radiator seems to be ok because when I flush the radiator, water flows freely. Could it be the radiator cap?