Film‐forming tendencies of some base fluids and viscosity modifiers

Abstract The film‐forming tendencies of selected mineral base oils and synthetic base fluids were investigated with and without conventional GL‐5 additive packages. A pressurised falling‐body viscometer and a concentrated contact simulator were used to measure low‐shear viscosities, central film thicknesses, and traction coefficients. Analysis of the mineral—based oils showed that a paraffinic base oil and a naphthenic base oil had similar film thicknesses, even though the naphthenic base oil has higher pressure‐viscosity coefficients. A very high viscosity index oil gave thinner film thicknesses and lower pressure—viscosity coefficients than the paraffinic or naphthenic base oils. Analysis of the synthetic base fluids showed that a PAO‐4 base fluid gave thicker film thicknesses than an ester base fluid. The analysis of fully‐formulated oils showed that the PAO‐4 oil containing a proprietary polyolefin provided a similar filnz thickness to the PAO‐4 oil containing a more expensive PAO‐100.