The viscosity and elastohydrodynamic (EHD) film thickness properties of binary blends of castor oil with polyol esters were determined experimentally. Predicted blend viscosities were calculated from the viscosities of the pure blend components. Measured viscosity values were closer to the values predicted using the Lederer model than the Arrhenius model. EHD film thickness data were mostly in agreement with the predictions of the Hamrock–Dowson model. Observed deviations of EHD film thickness were attributed to boundary film formation and thermal effects. Calculated effective pressure–viscosity coefficients, α, displayed a complex relationship with blend viscosity. At 40°C, the addition of 10% polyol esters resulted in a 12–17% drop in α of castor oil. Higher concentrations of polyol esters resulted in an increase of α. At 70 and 100°C, α displayed an almost linear dependence on blend composition. Copyright © 2011 John Wiley & Sons, Ltd.
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