Rheological Properties of New and used Brake Fluids

The operating as well as energy-efficiency criteria determine specific rheological parameters of car's fluids, including brake fluids. The aim of this paper is the determination of rheological properties of new and used DOT 3 brake fluid with the use of rotational cone-plate rheometer. The viscosity and flow curves of brake fluids were determined at ≈ 20oC and ≈ 80oC. The results of tests showed differences between new and used brake fluids. It was noted that used brake fluid was characterized by lower viscosity and higher density. The viscosity was constant in the whole range of a shear rate. Additionally, the decrease of viscosity with the increase of temperature was also observed. The linear dependence between shear rate and shear stress for both tested brake fluids was noted. The aforementioned relationship enables to classify both new and used brake fluids as Newtonian liquids.