Radiator "Ambient" Temperature

Simply a 25F difference in their ratings. The figure is the temperature of the ambient air into which the radiator is rejecting heat at its given rate.

hmmm.....

So is it better to have a radiator rated at 140F or 115F (these are random numbers by the way)?

Does it mean that if it is rated at 115F it can keep the coolant cool when the surrounding air is 115F, but if the surrounding air is more than that, aka 140F, it will cause overheating? So if the surrounding (ambient) air gets real hot, say in an enclosure, you need a higher rated radiator?

To put it another way ; when the surrounding air is 115 degrees the radiator wiil maintain the coolent temperature at 140 degrees, a difference of 25 degrees

The same radiator can be rated at any temperature, so the 140F one is not "better" than the 115F radiator. Varying only the ambient air temperature, as the temperautre goes up, heat rejected will go down. You need to be concerned about the rating for your conditions which includes temperaures and flow rates on the inside of the tube and the outside.