Idling and boiling coolent issues
Look at the cooling system for the boiling over. Check for vacuum leaks for idle issues.
Top it off, leave the rad cap off, start the engine......then while its heating up quickly squeeze the top and bottom radiator hoses like you're priming a gas tank line. Do it like 20 times each. Even if it does splash up and out of the rad fil lcap while you're doing it. I did this a few weeks ago and it worked out all the air and the t-stat opened. It would not open while there was air in there and mine to started boiling out the cap.

