You may be right, I don't know what the temperature difference at 40,000 feet is between night and day. Google or Bard would probably tell me, if I could be bothered.
I do know the efficiency of an engine is calculated from Carnot's theorem. In layman's terms, the efficiency of any engine increases with increasing temperature differential between the operating temperature of the engine, and the atmosphere it exhausts to. It's why gas turbines are considerably more efficient than a steam engine.
I suggest you take your sarcasm, and stick it where the sun does not shine.