[ajohn]

My 1936 Oldsmobile with a stock straight eight engine was doing the same thing as your car.I put an entire box of granulated Cascade dishwasher soap in the radiator as I do in all my cars that overheat.The temperature dropped from 212 to 160 in one running of about five miles.This will not always work but it is cheap and is the only way I have ever found to clean the system without major work.It might work for you.