Air coming out of hose inside coolant overflow tank. Kia Sedona.

jenniferlm

So, my van was overheating after approx. 7 - 10 min. of idling or driving 2 miles or so. We found a split in a hose and replaced it and found the thermostat was stuck so we replaced that too. It is still overheating but there is no coolant loss anywhere. Oil is not milky, no fizzy air bubbles in the radiator BUT I noticed that the little hose inside the coolant reservoir or overflow tank is blowing out bubbles into the tank. (It looked like the water was boiling). Any ideas? Blown head gasket? Bad water pump? Air in the lines somewhere? And how do you tell? Also, there's a left and right head gasket, so how do you know which one is blown if that's the case? Please help! We cannot afford to put it in the shop or to waste any money on parts we don't need. Any advice appreciated!