Just thought I'd bump this thread and give some more info since it's linked in Unabomber's FAQ.
I did a coolant change the other day, which is the second one I have done on my car. First time, went off without a hitch. This one was a bit more frustrating. After I changed the coolant, the car would continuously overheat during my "test drives". At first I though "Oh crap, a head gasket is gone", because I thought I knew EVERYTHING about air being trapped in the system and I thought that I had it all out. I got frustrated last night and parked the car and let it sit. I knew that car ran perfectly befor I started futzing with it, so I gave it another try
I went to Napa today, got some PEAK Global to use for top-off. When I got home, I popped off the cap and just started compressing the upper and lower radioator hoses rapidly. I then could FEEL that there was absolutely NO COOLANT in the upper hose. It was all air. (If there is air in it, it will be VERY easy to squeeze - you will notice it is harder to squeeze as water enters the hose) I started "massaging" the hose and I could feel the coolant start to work it's way into the hose as I made a swushing motion with my hand. I then started the car and heat cycled the engine, letting the fans kick on and off a few times, all the while, I was squishing the hose and topping off the coolant with distilled water and PEAK. Turns out, for whatever reason, a TON of air got into the system this time and that is what caused my problem. I took the car for a drive and the temp needle stayed right where it needed to be.
DON'T GIVE UP! KEEP MASSAGING YOUR HOSES UNTIL YOU GET ALL OF THE AIR OUT! IT MAY TAKE A VERY LONG TIME!!