Today's high-power-output two-cycle engines require special motor oils for satisfactory performance. Base oils, either alone or fortified with conventional passenger-car motor-oil additives, satisfy neither small air-cooled nor large water-cooled outboard engines. Additives designed specifically for two-cycle engines can provide the performance properties needed. However, good performance in one engine does not guarantee like performance in. an engine of different design.
As the oil is supplied with the fuel, gasoline additives have a pronounced effect on the performance of motor oils. Lead reduces engine cleanliness and increases harmful combustion-chamber deposits. Phosphorus additives promote spark-plug fouling and preignition.