Thanks for the reply. I restricted air flow to force the auxiliary electric fan to activate and also to see if I could force the temperature above 210.

Thanks for all the input everybody. I'm still researching the why and of course which way to go on a replacement. I took the leaker to a radiator repair guy today and ponied up the money to have it pressure tested, I knew it leaked and suspected it was tubes to pan but I wanted to know where and how bad. This guy has been in the radiator business since we were both in our twenties, a long, long time ago. Before he even tested it he told me where he thought it would be leaking and he was correct. Third tube down on the intake side, the tube to pan joint was just pouring. He said electro-chemical erosion on the interior of aluminum radiators, especially at the intake side, where the hot coolant out of the cast iron block first hits the aluminum is a very common problem. Since this is the fifth radiator in as many years he suggested having the coolant tested for contamination. Better to solve he problem rather than keep throwing radiators at it. Laboratory test kit is fifteen bucks from the local Caterpillar service center. The Cat service guys said they had a problem some years ago with a couple of models eating up aluminum thermostat housings from the inside, and their fix was to go through and ground everything; the design relied on the starter ground and it just wasn't adequate. Solder wick is cheap and the radiator mounting is fairly well isolated, so maybe the Caterpillar guys are onto something.

"Little by little!"