I guess this notion was incorrectly instilled in my mind when I was a young man. I remember how the crop duster pilots would shut down and not fly in the heat of a late summer day. They told me they lost lift due to the thin air.
The link below tells of how the Phoenix airport can be shut down down due to unsafe flying conditions created by air at high temperatures, look under the transportation heading.
Again, thank you for correcting my statement about how a variance in air temperature might have an effect on the performance of a vehicle, aerodynamically.
Bondo
Impacts of Temperature Extremes