Clean radiator, cool engine, coolant PH, flow, fans, shrouds.

ramcharger,
well the density of air (due to altitude or other factors) and its ability to conduct and or absorb heat is in my "half assed astronaut" opinion a reasonable concern. It would seem that running at 5000 feet where you have a thinner air and less conductive medium would lessen the efficiency of any atmospheric cooling system. :) . Further discussion seems highly important to the overall success of any and all cooling situations.