Rapeseed oil was thermally treated at 150 degrees C for 45-285 min after addn. of maleic anhydride (1) (2%) and stored for 20 mo at ambient temp. The products were analyzed for kinematic viscosity, acid and peroxide nos., chem. compn. (get permeation chromatog.) and lubrication properties in the ball-plate (steel-steel) system. The addn. of I resulted in an increase in the seizure load and storage stability (esp. for low viscosity samples).