PURPOSE of this paper is to discuss a number of the factors that should be considered in the selection and use of lubricating oils with particular emphasis on the need for engine or service tests, as the usual specifications are only identifying tests indicating general characteristics.
The authors show that some of the performance characteristics of lubricating oils, such as limiting cranking temperatures, oil mileages, and gear-shifting temperatures, can be predicted from viscosity determinations, but the other items of interest to the users, such as stability, ring-sticking, gumming, and wear, cannot be predicted from inspections. Data are presented to show how compounded oils meet the severe present-day conditions of increased mechanical and thermal loads imposed on the lubricating oil especially in high-speed diesels. Compounded oils, they point out, cannot be judged by simple laboratory tests, and should therefore be selected on a basis of their performance in full-scale engines.
Such physical tests as gravity, color, flash point, fire point, viscosity, pour test, Conradson carbon, and Neutralization Number are discussed in the light of their present usefulness. The significance of viscosity and viscosity index is explained fully.