Due to engine oil consumption, over 90% of the incombustibles in the diesel particulate filters (DPF) are derived from organometallic lubricant additives. These components are derived from calcium and magnesium detergents, zinc dithiophosphates (ZnDTP) and metal-containing oxidation inhibitors. They do not regenerate as they are non-volatile metals and salts. Consequently, the DPF has to be removed from the vehicle for cleaning.Ashless oil could eliminate the need for cleaning. This study initially focused on development of an ashless oil, but eventually concluded that this oil could not meet the valve-train wear requirements of the API CJ-4, SN/ACEA E9 oil categories. However, a zero-phosphorus oil with no ZnDTP and an extremely low sulfated ash of 0.4% demonstrated that it could meet critical engine tests in API CJ-4/ACEA/SN.The above oil, which has been optimized at 0.3% sulfated ash, has proven field performance in Cummins ISX with DPF using ultra low sulfur diesel (ULSD). This was verified by engine inspections and used oil analysis at 60,000 miles (97,000 km) oil drains. DPF cleaning determined at 95% confidence level that the 0.3% ash oil produced less incombustibles than a 1.0% ash API CJ-4 oil. Reducing the engine oil's ash by 70% resulted in a 78% reduction in DPF incombustibles. Consequently, the 0.3% ash oil will minimize DPF maintenance while also providing engine durability.