UPDATE - 1 year later, I have added about 1 quart of antifreeze over the past year. However car is running on the hot side around 207 degrees. There is no sign of foam in the oil or the antifreeze.
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.