It is shown that the operation of engines on crankcase oils containing appreciable amounts of zinc dialkyl dithiophosphate can increase the small-scale roughness of the lifter-foot surfaces. In addition, the small-scale roughness can be reduced by subsequent operation of the same engine parts on oils containing no zinc dialkyl dithiophosphate. This change in roughness coincides with a change in reflectivity that can be detected visually.