Jose wrote:
There was a discussion in my club about leaning the engine (of our
cherokees) below 5000 feet in cruise. This was prompted by the
observation in the manual that the engine should be leaned above 5000
feet at all times in cruise, and below 5000 feet at the pilot's
discrescion. So, how should the pilot discrede? The old timers seemed
to agree that:

1: at low power (say 65% or less) you can't hurt the engine by leaning
to peak EGT, but...

2: at high power (above that, including the 75% many like to fly at to
go fast) one should only lean if it's cold enough, and that the best
thing to do is run full rich if you're in doubt.

This runs counter to my understanding and practice. I lean (50 degrees
ROP) in cruise at all altitudes, including the ones where I can pick the
leaves off the trees, and I run 70-75% power. Running full rich is just
dumping a third of the fuel out the tailpipe.

Either the Warrior II POH or my instructor said to lean above 3000. But
I couldn't find it after a quick look at an ARROW POH. Nonetheless, I
would follow the manual and if it didn't mention a specific procedure, I
wouldn't do it.