I Have a 2005 Ram 2500 5.7L Hemi 4x4 the radiator had a leak so I just replaced the radiator and added fresh coolant started it up and let it in my driveway it ran hot and pushed all the coolant into the coolant reservoir and it had never done this before. It has a new water pump that was installed a few months ago. what could the problem be?

I'd say there were still air pockets in the radiator and block. Personally I would fill the coolant overflow bottle all the way up, make sure the radiator cap is on properly, because as the engine cools it will start drawing back coolant from the bottle. Patience....

Fill the radiator about 3/4 leave the cap off and start the truck you may see the circulation begin once the thermostat opens If not ... your back to square one and I would remove the thermostat ... put it in almost boiling water and see how far it opens. Some cooling systems require that a special procedure be followed when refilling or you will get pressure voids and no flow

Ok I'll go and try running it with the radiator cover off and see what happens. I don't want to blow my Head Gaskets though

I don't want U to drive it ... just run it with the cap off to get circulation without pressure It won't take long for the water to get hot enough to boil .... then you can fill it completly and put the cap back

Thanks Guys. I ran it for an hour. half hour with the cap of and half hour with the cap on and it never passed the center mark between C and H. Thanks again