Another "Hot" problem

Not enough radiator, collapsing lower hose, or DEFECTIVE radiator. "Oldmanmopar" posted this idea some time ago, and it turned out to exactly what I believe to wrong with my car. He claims the finds can crack loose from the tubes over time, with multiple thermal cycling, showing the radiator to be clean and having good flow, yet actually unable to reject heat.

My own car (at the time) a mild 360, was overheating on the highway, the faster the more heat. I swapped in a "junk" late model SLANT rad. Both rads were two core, the original old 67, and the slant, a 73--74 car.

INSTANTLY the temp dropped like a rock, no other changes.