Thanks Jerry. I'll try the 4lb cap and take the truck for a run. Everthing has been rebuilt on this truck. I don't know what thermostat is in at the moment but this weekend I'll drain and flush the system and pull the thermostat to see what one is in. I checked the water temp and the gauge is working ok. Its coming into summer in this part of the world so its a good time to get this sorted. Thanks again for the help mate.

Bob