Originally Posted by
thing
I was always taught to lean from the very first flight powered flight I had, don't know whether that's unusual or not. Something I always do when cruising regardless of altitude.
You had a good instructor
. Leaning any Lycoming or Continental engine at or below 75 % power
is permitted at any altitude. Running full rich all the time fouls the plugs and wastes gas. The engine should always be leaned in cruise flight even if it is only for short distances.