Did you fill the rad and then let it idle with the cap open to work out air bubbles?
Great tip!!! I can't believe how many people I talk to on a daily basis that don't know how to fill a radiator! Always leave the cap off and let the thermostat open and close at least once before putting the cap on. This will let all the air pockets out of the cooling system. You may also want to check your radiator cap with an actual coolant pressure tester to make sure the relief spring is working right. If it is worn out it will not hold pressure in the radiator and it can bleed off coolant. Also may want to change the thermostat out if you haven't already.
