Air Bubbles In Radiator.
 

I'm the same guy that has written several threads about my my rebuilt 400 motor in a 67' GTO wanting to run hot. Got about 150 miles on my rebuild now. Today I took the Harrison radiator cap off and let the motor run about 10 minutes at idle. Temp. went to about 220, radiator "ran over" about a quart of antifreeze, and I watched the fluid inside the top radiator tank. Every 4 or 5 seconds I would notice a belch of big air bubbles. No exhaust fumes or smoke just air bubbles. Let it run for another 10 minutes or so and kept it relatively cool (200 to 205) by keeping the rpm around 2,000 or so. Should there be air bubbles in a radiator? Oil is clear and clean, no milky appearance. If these bubbles shouldn't be there how do you purge them out of your cooling system? Could they be the reason for my overheating problem? I just don't know what air bubbles signify or if it's normal or not. Thanx.

did you ever watch of pot of water starting to boil on a stove, eventually bubbles are seen in the water, then more bubbles, then more and finally a rolling boil. those bubbles you see after the radiator was above 220 with the cap off, are those same bubbles of boiling fluid starting to go from a liquid to a gas when the cap is off. if you run the rpms up, you move more hot fluid and release more vapor bubbles from out of the antifreeze and water. put the cap back on, because that is the cause for the bubbles.