At what altitude will a piston engine run coolest-high or low

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Will a piston (non-turbo) run cooler at altitude where the outside
air is cooler or lower where the air is more dense ?


-- Evan Salant, August 4, 2006


The turbocharged engines that use high power at high altitudes run very hot indeed. The cylinders are around 325-400 degrees F so even on a warm day the outside air is much cooler than the cylinders. There might be some kind of optimum at around 5000' if the lapse rate is high and it is much cooler up there than at sea level.

-- Philip Greenspun, August 7, 2006