Engine Bearing Oil Film Thickness Measurement and Oil Rheologh - an ASTM Task Force Report

An American Society for Testing and Materials (ASTM) Task Force was formed in 1984 to: 1) establish a series of reference oils, 2) measure the minimum bearing oil film thicknesses provided by the oils in fired engines, and 3) interpret the results in terms of oil rheological properties. Minimum oil film thickness (MOFT) measurement and analysis techniques using a capacitance method were developed. At steady-state operating conditions, laboratories evaluated a matrix of eighteen monograde and multigrade oils, blended with four widely-used viscosity index improvers (VIIs). Analyses showed increasingly better correlations between MOFTs and viscosities of both single grade and multigrade oils as temperatures and shear rates used to calculate viscosities more-closely approximated in-bearing conditions.