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Recent advances in the powertrain design of gasoline engines to meet environmental regulations have posed new challenges to the engine oil development. Smaller displacement engines, often with turbochargers, developed to meet higher fuel economy standards demand higher performance engine oils in conventional areas (oxidation and deposit control, fuel economy), and completely new areas (Low-Speed Pre-ignition [LSPI], turbocharger performance). Formulating engine oils which can simultaneously meet these competing demands will become more complex with increasing performance requirements. Of particular interest for upcoming engine oil development is the phenomenon of low speed pre-ignition (LSPI). LSPI is an abnormal combustion event in which lubricating oil has been observed to play a role.

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.