Trunk piston marine engine lubrication, when the engine is fueled by heavy fuel oil, is effected by a composition comprising a major amount of an oil of lubricating viscosity and a minor amount of one or more phenolic compounds comprising distilled cashew nut shell liquid or hydrogenated distilled cashew nut shell liquid. Asphaltene precipitation in the lubricant, caused by the presence of contaminant heavy fuel oil, is prevented or inhibited.