This paper reviews the development of the first fuel economy engine test method for heavy duty diesel oil, as well as the new JASO DH-2F category introduced in April 2017 [1][2][3], which adds a fuel economy requirement to the JASO DH-2 requirements in the JASO M355:2015 standard. Recently, better fuel economy is required heavy duty diesel vehicles as well as gasoline vehicles. Therefore, advanced technologies have been applied to improve diesel engines, as well as diesel engine oils and additives, and achieve better fuel economy. However, the Automotive Diesel Engine Oil Standard (JASO M355) applied in Japan as a standard for diesel engine oils does not include any fuel economy requirements. Consequently, a JASO Diesel Engine Oil Standard Revision Task Force (Task Force) consisting of organizations from related industries, including the Japan Lubricating Oil Society (JALOS), developed an engine test method using a Hino N04C engine equipped with the latest technologies to comply with the 2010 Japanese emissions regulations. The method measures fuel economy performances for fresh and aged oils in JASO-specified engine tests using the N04C engine. The specified test protocol is based on the governmental test method for heavy duty vehicles and evaluated through comparison with Society of Automotive Engineers (SAE) 30 oil. The new test method can differentiate fuel economy performance for different viscosity properties of SAE 5W-30s. The minimum criterion for the fresh oil fuel economy improvement rate was set to 3.7%, and the sum of the improvement rates for fresh and aged oils was set to 6.8%.
