> Driving through the Rocky mountains will reduce mpg significantly for an internal combustion engine as well. Do you mean it will reduce the mpg because of re

> Driving through the Rocky mountains will reduce mpg significantly for an internal combustion engine as well. Do you mean it will reduce the mpg because of reduced air density, or because of temperature as well? I thought the efficiency of an ICE was dependent on the difference in temperature it creates between the combustion and the coldest part of the cycle. It seems efficiency would improve in cold temperatures because less energy would be wasted cooling the engine since the incoming air is doing that.