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The interest on improving fuel efficiency of vehicles is increasing day by day. Fuel efficiency standard for diesel commercial vehicles such as buses and trucks was published in Japan. Using a fuel efficient engine lubricant is one of the effective paths and there are several 5W-30 diesel engine lubricants in Japanese market which are advertised to give a benefit on fuel efficiency against 10W-30 oil. During the development of 5W-30 fuel efficient diesel engine oil, it was revealed that the piston underside was significantly blackened by the detergency engine test (JASO M 336: 2014). In this paper, the causative agent which blackened the piston underside was investigated and the formulation to inhibit this blackening phenomenon was studied. Through several tests, it was considered that use of poly methacrylate based viscosity index improver and ester type friction modifier deteriorated detergency performance.

This paper reviews the development of the new four-stroke diesel engine oil standards, JASO DH-2 and DL-1 (JASO M335-05) for Japanese automotive diesel engines equipped with after treatment devices, e.g. Diesel Particulate Filter (DPF) to meet the new long-term emissions regulations. These standards have been introduced in Japan in April 2005. The standards prescribe the minimum performance for engine oils conforming to Japan-made four-stroke diesel engines with aftertreatment devices using low sulfur diesel fuel (less than or equal to 0.005 mass % sulfur). The engine test requirements for these new standards are basically the same as those of the JASO DH-1 automotive diesel engine oil standard (JASO M-355 2000) to meet engine oil performances with soot dispersancy (ASTM D 5967-99), piston detergency (JASO M336-98), thermal and oxidation stability (ASTM Seq. IIIE and IIIF), and anti-wear performance (JASO M354-99).