Characterisation of the Viscoelasticity of Engine Lubricants at Elevated Temperatures and Shear Rates

Most automotive multigrade oils contain high molecular weight polymeric viscosity index improvers (VIIs) and are to a greater or lesser extent, viscoelastic liquids. A way of characterising lubricant viscoelasticity (as typified by the first normal stress difference) using slit die rheometry is described in this paper. This technique has been applied to measure the viscoelasticity of several conventional multigrade oils at temperatures and shear rates close to that experienced by the lubricant in an automotive journal bearing. Additionally, the potential of slit die rheometry as a technique to measure the viscosity of engine oils at shear rates up to 2 X 10⁶s^-1 is assessed.