The Air bubbles in fondant icing?

Can a leaky water pump in a 1998 Subaru Forester produce air bubbles in the overflow reservoir?

• The water pump gasket in my '98 Forester (130k) recently began to leak, and I will be replacing it in the next couple days. I noticed a stream of bubbles in my overflow container, though, and am wondering if it might be bad head gaskets making the air bubbles. The bubbles only appear after the engine is warmed up, like after a drive around town - there aren't any bubbles when the engine is cold. Is it possible that these air bubbles are coming from the leaking water pump? I hope so, because I'd much rather replace the pump than the head gaskets! There is no water in the oil, and the compression checks out ok. One thought came to mind: if the bubbles only appear when the engine is hot, then could it possibly be the heads warping with increased temp? They are aluminum heads, with a cast iron block. If anyone has ever seen/heard of a leaky water pump introducing air into the cooling system, please let me know!

• Answer:

  Normally no,coolant leaks are replaced by gravity from the radiator and expansion bottle,air is fed back by expansion bottle cap. Have the gasket replaced it will tell it all.