LS Overheating

[DerickAB72]

So I finally registered my 2001 LS that I brought last week and driving it home today it started over heating. I noticed the heat was blowing cold and then when I stopped the water was bubbling and so on. I imediately thought thermastat so I went out and brought one. When I got to my dads house to let it cool off for a few minutes I noticed the level was low so I decided to top it off and see what happens during the drive home. Any idea as to what I can look for next?

 

[Tyson]

Might be an air bubble. Mine overheated after replacing the coolant puke tank.
I heard it bubbling in the lines and after bleeding it everything returned to normal.