There's always going to be an air pocket when you first fill up the radiator and cooling system starting with a dry engine. Take the radiator cap off, run the engine until the thermostat opens (you'll see water passing through the top tank or the water drops). Fill the radiator up again and wait for the radiator to settle (may have to add water again): water moves but no more air bubbles. With continued running of the car, the water will expand and pop out of the tank with the cap off.