There's a bleeder valve for the cooling system and it's on the top of the manifold. The bubbling is most likely as desceribed - air in the system. Just get the engine good and hot and with the heater on, open the bleeter valve until all air is out (that is, you start getting coolant out of the bleeder valve). Make sure to watch your coolant level too so it doesn't run low at the same time.

HTH!

-G