When I fill the radiator, I leave a wide mouth funnel in the inlet, and burp the system by slowly squeezing the upper radiator hose. You will see bubbles come up from the funnel. Keep adding water and squeezing the hose until the bubbles stop. Some experts say to break in the motor with straight water and afterwards switch to a mix of water and anti freeze. I suppose that is in case of leaks? Some believe that water transfers heat better. Maybe try using Water Wetter or some other coolant aid.