With a clean radiator, the top tank temperature should be close to the same as the thermostat setting. The early radiators can't stand much pressure on the core, so getting way above boiling like a modern radiator and allowing the pressure to keep the coolant liquid isn't an option. The boiling point rises 3 degrees for every pound of pressure, so a high-pressure radiator can get up to 250 degrees or so with enough cap pressure. The old stovebolt systems shouldn't get above 200, even on a hard pull. 160 to 180 is better!
Jerry
