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Volume 46, Issue 2 (March 2018)
An Improved Method for Calculating Viscosity Index (VI) of Low Viscosity Base Oils
(Received 5 June 2015; accepted 16 December 2016)
Published Online: 2017
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The phenomenon of “VI droop” has been observed for many years for low viscosity oils within a given family of base oils. Whereas base oils with 100°C kinematic viscosity greater than 4 mm2/s (cSt) easily conform to the nominal API base oil group of its family, 2 and 3 mm2/s products often do not. For example, the low viscosity members of the NEXBASE® API Group III family are technically Group II oils because their viscosity index values fall below the 120 minimum established for Group III. Although it might appear that the low viscosity oils are of lower quality than their higher viscosity siblings, all are produced by the same refining technique and share the same rheological profile. As formulated engine oils evolve into lower SAE viscosity grades in the future to meet OEM demands for greater fuel economy, lighter base oils will become increasingly important formulating components. Therefore, a study to understand the underlying cause(s) of VI droop for low viscosity base oils was undertaken.
Covitch, M. J.
The Lubrizol Corporation, Wickliffe, OH
Stock #: JTE20150242
Title An Improved Method for Calculating Viscosity Index (VI) of Low Viscosity Base Oils