This paper deals with and records the results of many years of designing, building, and testing lubricating systems for internal combustion engines. The first consideration, will be the brief presentation of historical facts leading to the final designs, with records of results to date. To illustrate briefly what I have in mind as improvements, I will use a series of slides, some of which, incidentally, served as illustrations in an S.A.E. paper presented by the writer to the Northern California Section on April 13, 1939, entitled, “Oil Filters”. In this previous paper a detailed description of the various filters was given and also engine design and operation problems were related, thus justifying the need of a positive means of preventing grit in the lubricating oil from entering the bearing surfaces during operation of the engine. In view of this fact, this paper will deal only briefly with the design of the various types of filters and be confined almost entirely with the results of actual tests, both field and laboratory, describing as best I can, in the time available, what actually happens to engines, filters, and lubricating oil during normal service.