Recently, deposition of ash derived from engine oil on the surface of a diesel particle filter (DPF) has been reported to worsen the performance of the DPF. It is generally known that phosphorus in engine oil is adsorbed on the surface of an automotive exhaust catalyst and reduces the performance of the catalyst. Thus, the amounts of ash and phosphorus in engine oil have been decreased. We have developed a non-phosphorus and non-ash engine oil (NPNA) that does not contain metal-based detergents and zinc dialkyldithiophosphate (ZnDTP). We performed a performance test for NPNA using an actual engine and reported that the piston detergency and anti-wear performance of NPNA were sufficiently high.However, the piston detergency of NPNA required further improvement when engine running conditions were more severe. We performed a hot tube test to evaluate the piston detergency of NPNA at high temperatures and developed additives (ashless detergents) that did not contain ash (metallic elements).We then performed a Caterpillar 1N engine test that was regulated by American Society for Testing and Materials (ASTM) D6750, and we evaluated the piston detergency of NPNA, in which a candidate ashless detergent was mixed. The candidate ashless detergent considerably improved the weighted total demerit for 1N (WDN) and exhibited excellent piston detergency.