The strainers and filters used with Navy diesel engines are a part of what is generally referred to as the LUBRICATING OIL FIL-TERING SYSTEM. Currently, engines use a system known as the FULL-FLOW FILTER-ING SYSTEM. You should refer to figures 8-9 and 8-10 as you read the descriptions of this system.

In the full-flow filtering system, all the oil supplied to the engine by the oil pump normally passes through the filter elements, which remove impurities of 25 microns and larger.

NOTE: One micron is one millionth of a meter, or thirty-nine millionths of an inch. An ordinary grain of table salt is about 100 microns, and 25 microns is approximately one-thousandth of an inch.

There are only two conditions where unfiltered lubricating oil is supplied to the engine: (1) when the lubricating oil is cold (high viscosity), and (2) when the filter element is clogged. When one of these conditions exists, a bypass valve opens and a portion of the oil is bypassed around the filter element. The action of the bypass valve results from the resistance of the filter element to allow the oil to pass through it. The resistance creates enough back pressure for the spring-loaded bypass valve to open.

A secondary filtering system, which operates independently of the primary system, is currently being installed on various marine diesel engines.

Figure 8-9.-Schematic diagram of a typical lubricating oil system in a General Motors series 71 in line diesel engine.

Figure 8-10.-Lubricating oil system in a Caterpillar diesel engine.

The secondary system will filter impurities from the lubricating oil through a 5-micron filter, which is a much finer medium than the 25-micron filter used in the primary system. FLOW OF OIL THROUGH THE DIESEL ENGINE LUBRICATING OIL SYSTEM

Even though the design and arrangement of various diesel engine lubricating oil systems may appear to be different, the systems of most engines are similar in many aspects. So far our discussion has covered the external components of the engine lubricating oil system. Our discussion will now cover the flow of the oil through both the external and internal components of the General Motors series 71 diesel engine and the Caterpillar diesel engine. Learning to trace the flow of oil through the complete lubrication oil system of a diesel engine will be quite helpful to you when you are dealing with lubrication difficulties.