SYMPOSIA PAPER Published: 01 January 1989

Change of High-Shear-Rate Viscosity of Engine Oils During Use: A Review


It has long been known that the kinematic viscosities of multigrade engine oils change with use, the typical pattern being an initial decrease followed by a gradual increase. Recent work has shown that the patterns of change of the high-temperature, high-shear (HTHS) viscosity are different than those of the kinematic viscosity. These results, coupled with recent bearing oil film thickness results, suggest that kinematic viscosity changes are less significant in the operation of the bearings of engines than has been assumed. The pattern of HTHS viscosity change has been found to depend on both viscosity index (VI) improver type and engine test. Oil-thickening effects tend to be more prominent in the HTHS viscosity patterns than in the kinematic viscosity patterns.

Author Information

Alexander, DL
Texaco Research Center, Beacon, NY
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Developed by Committee: D02
Pages: 60–73
DOI: 10.1520/STP23003S
ISBN-EB: 978-0-8031-5105-5
ISBN-13: 978-0-8031-1280-3