Along with the "usual suspects" not enough rad, big fan, shroud and all the rest, "Oldmanmopar" awhile back posted a theory which I think "was" my problem
I HAD the factory 273 original rad, and whether 360 or 318, it would run pretty warm
I TRIED successfully a junk 73 SLANT SIX rad in the car, and it cooled right down
Except for physical design the two are close to the same.....two core rad, on the old round tank, the other the more modern late style tanks.
His theory? That various thermal expansion (and I'm thinking partial freezing along with pressure) causes the tubes to deform and otherwise become SEPARATED from the fins, which leaves you with a rad that LOOKS fine, FLOWS lots and lots of coolant, and does not transfer very much heat.
