The lubricating oil systems of most engines use coolers (heat exchangers) to maintain the oil temperature within the most efficient operating range. Oil, passing through the operating engine, absorbs heat from the metal parts. Since engine oil is recirculated and used over and over, it is continually absorbing additional heat. Unless the heat is removed, the oil temperature will rise to excessive values. At extremely high temperatures, oil tends to oxidize rapidly and form carbon deposits. Excessive engine operating temperatures also cause an increase in the rate of oil consumption. Consequently, oil coolers are required to remove excess heat from the oil so that the oil will retain its lubricating qualities.

The coolers used to remove heat from lubricating oil are of the same type as those used to remove heat from other fluids common to internal-combustion engines. These coolers are referred to as shell and tube, strut tube, or plate tube coolers. (These coolers were discussed in detail in chapter 7 of this manual.)

FILTERING DEVICES

Oil must be clean before it goes into the lubricating system of an engine. Oil must also be cleaned regularly while it is being recirculated through the engine. Dust and dirt particles from the intake air get into the oil system. Flakes of metal from the engine parts are also picked up and carried in the oil. Carbon particles from incomplete combustion in the cylinders work into the oil. Heat causes the oil itself to deteriorate and form sludge and gummy material which may coat load-bearing or heat-transfer surfaces, or circulate through the oil system. Some water will get into the oil, even when precautions are taken.

The lubricating oil system of an engine uses strainers and filters to remove abrasives and foreign materials which tend to increase wear of engine parts and cause the lubricating oil to deteriorate. A variety of strainers and filters are used in Navy installations. According to Navy terminology, all metal-edge and wire-mesh devices are classed as STRAINERS. Devices that have replaceable, absorbent cartridges are called FILTERS. Filters remove smaller particles than strainers. The location and number of strainers and filters will vary, depending on the type of installation.

Strainers

Lubricating oil strainers may be either simplex or duplex. A duplex strainer is two strainer elements in one assembly. A manual valve directs the flow of oil through either of the elements. When duplex strainers are used, one element can be bypassed, and the element can be removed and cleaned without disturbing the flow of oil through the other element to the engine.

Every approved lubricating oil strainer has a built-in, spring-loaded or differential area, pressure-relief valve. The valve must be sufficiently large to bypass all of the oil around a clogged strainer to maintain an uninterrupted flow of oil to the engine.

Metal-edge strainers consist of a strainer element surrounded by a case that serves as a sump to collect foreign material and water. The element has an edge-wound metal ribbon or a series (stack) of edge-type disks. Most strainers have devices for manually rotating the strainer element against metallic scrapers, which remove the material caught by the element. Strainers usually have vents for releasing air from the system.