UPDATE - 1 year later, I have added about one quart of antifreeze over the past year. However the car is running on the hot side around 207 degrees. There is no sign of foam in the oil or the antifreeze. I started adding antifreeze every few weeks.
UPDATE - After 14 months it is going through a quart of antifreeze every two weeks. There is some foam on the antifreeze filling cap.
My HHR overheated again only two months after the last time that I tried to fix it. The radiator was down about two quarts of fluid. This time I decided to spend some more money and get something that stays in the radiator. It is called "Bar's Leaks Professional HEAD SEAL Blown Head Gasket Repair" and runs about $45. Just add 1/2 the container to the antifreeze - for a 4 cylinder engine.