Effect of Low Viscosity Passenger Car Motor Oils on Fuel Economy Engine Tests

The fuel economy performance of passenger car vehicles has been an area of keen focus due to recent environmental regulations. Various efforts such as the development of new engine technologies have been undertaken to improve the fuel economy performance of these vehicles. Engine oils have also been targeted to contribute to better fuel efficiency. This has been done by introducing new lubricant additive technologies and low viscosity grade oils. In the latter case, passenger car motor oils are about to enter into a new generation in which the lower viscosity grade SAE 16 has been approved and discussion has started on the specification of viscosity grades lower than SAE 16, although SAE 0W-20 viscosity grade is the lowest in the SAE J300 specification during last decade. Nevertheless, additive technology is also important, as we previously reported that simple reduction of viscosity grade is not a solution to improve fuel economy performance in the Sequence VID test.

In this paper, the increase in the severity of boundary lubrication conditions with the use of lower viscosity grades is shown. Lower viscosity grade oils such as 0W-16, 0W-12 and 0W-4 were also evaluated on the motored engine friction torque test and showed similar behavior to the Sequence VID test. Friction modifiers were demonstrated to improve the friction properties under boundary lubrication conditions while retaining the benefit at hydrodynamic lubrication conditions.