The impossible to solve overheating problem

RustyRatRod said
You also commented that the radiator is not clogged. How do you know? Have you had it flowed by a competent radiator shop? You could have a situation where the radiator has become restricted from rust and debris from the engine over time. You would not be able to tell unless you had the radiator flowed.

I tested by just filling it multiple times and seeing that it emptied very quickly. So like your saying its not the best test. It is possible that it has become clogged, but its hard to believe that both radiators have become clogged while one in use and one on the shelf.