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The ability of oil to retain its viscometric properties is particularly important in Heavy Duty Engine Oil applications to prevent wear and maintain intended levels of oil pressure. It is known that mechanical shearing of the oil, fuel dilution, oil oxidation and soot level all affect the aged oil kinematic viscosity at 100°C (KV100). For API CJ-4, as well as for many OEMs, an oil's KV100 must stay within the original viscosity grade as defined by SAE J300 after 90 cycles in the Kurt-Orbahn (KO) apparatus. This study investigates the effect of polymer chemistry and structure on extended shear stability of lubricating oils by evaluating the performance of two Viscosity Index Improver (VII) chemistries, Olefin Copolymer (OCP) and Hydrogenated Styrene Isoprene (HSI), under more severe shearing conditions than required for CJ-4. These technologies were evaluated in the KO shear test up to 700 cycles and the KRL shear test up to 8 hours.

The fuel economy performance of passenger car vehicles has been an area of keen focus due to recent environmental regulations. Various efforts such as the development of new engine technologies have been undertaken to improve the fuel economy performance of these vehicles. Engine oils have also been targeted to contribute to better fuel efficiency. This has been done by introducing new lubricant additive technologies and low viscosity grade oils. In the latter case, passenger car motor oils are about to enter into a new generation in which the lower viscosity grade SAE 16 has been approved and discussion has started on the specification of viscosity grades lower than SAE 16, although SAE 0W-20 viscosity grade is the lowest in the SAE J300 specification during last decade. Nevertheless, additive technology is also important, as we previously reported that simple reduction of viscosity grade is not a solution to improve fuel economy performance in the Sequence VID test.