Originally Posted by RickRick
How much coolant was lost? If more than a quart or two, did you refill the neck? Not the overflow. If so, when the car is warming up squeeze the upper radiator hose to burp the coolant back three the system and run your heat to get the coolant threw the heater core. There most likely air in your lines.
Definitely could be air in the system. Try purging the air, filling fully with coolant and let us know how it works out.