THIS paper presents the results of oil consumption tests in laboratory engines equipped with external sumps, providing separate cylinder and overhead valve lubrication systems. These results show that from one-third to two-thirds of the oil consumed by the engine was lost by way of the valve assembly.
It was also found that, although viscosity is the most important oil property affecting consumption, over one-third of the reduction in consumption in going from a typical SAE 10 to a typical SAE 30 oil is due to the decrease in the volatility of the blend. The results are interpreted in terms of oil-loss mechanisms governed by oil viscosity and volatility. The application of the results to the formulation of multigrade oils is demonstrated.