misreading temp gauge

I've posted this several times because in my case the change was so incredibly dramatic Oldmanmopar posted this I do not take credit

My old original rad was tested by a shop and they said it "should cool." It did not. I swapped in a used, unknown, /6 rad, and the change was dramatic. The temp immediated dropped. Oldmanmopar thinks that years of thermal cycling causes the fins to crack loose from the tubes, reducing head radiation and heat exchange. This makes some sense, because my old rad flows lots of water. Its simply does not cool very well.

Both rads are two core, similar size, one the old 67 round tank, 273, the other the newer 73 style newer style.