ABSTRACT
The primary function of a lubricating oil is to provide a hydrodynamic film between moving parts. In developing new engine oils, researchers often concentrate on the newest engine performance specifications, for example International Lubricants Standardization and Approval Committee GF-5 or American Petroleum Institute CK-4, since they highlight the most critical engine performance characteristics that a lubricant must meet. Base oils and polymers are the key engine oil ingredients that influence low and high temperature rheological properties of engine oils. A way to improve fuel efficiency is to operate engines under high torque and low speed conditions. Engine operating conditions and fuels have changed significantly and as a result engine oil quality has improved to adapt to more severe conditions. In addition, it is important that engine oils improve vehicle fuel efficiency and are compatible with vehicle systems designed to reduce vehicle emissions.
