Mikemnh,

I have seen engines with up to 20 gallons under the belt, and the coating still in place, albeit slightly thinner in local spots. You may fly at a field where the engine ingests air that is polluted with dust particles? In that case use of an air filter could be beneficial, or start the engine with the plane placed on a mat to avoid sand being swirled up.

IMHO, the very slight wear of this coating, which is only a few microns thick, can not be held responsible for the black goo. More so because my Quadras and Ryobis all had it. They do not have the graphite piston coating that MVVS has.