The Stovebolt Site Forums The Shop Area Engine Shop Rebuilt 1948 Chevy 1/2 ton 216 C.I. overheats

If your radiator doesn't leak, a radiator shop (assuming one still exists in your area) could clean it up for you. Years ago, I had a radiator that I was having trouble with and took it to a shop to have it "rodded out". They removed the top and ran rods down thru the tubes to clean the crud out of them. It may be possible to get yours clean by filling it with a mild acid solution and letting that sit for a few days.Lay it on it's face and fill it with the solution (not while installed on the engine.) Use something like this:

[on edit] I went back and read your first post. You say it's getting to 212F, but is it boiling over? A 50/50 mix of coolant raises the boiling temperature significantly, so if you're not loosing coolant, your engine isn't "overheating." Changing to a lower temperature thermostat doesn't help, but just opens completely at a lower temperature, which is not necessarily good. If the radiator is doing it's job, it should keep the engine at roughly the thermostat temperature.