Lesson 4/Learning Event 2
Oil leaking around the rear main bearing oil seals usually soaks the clutch disk facing and drips out through the
drain hole in the bottom of the engine flywheel housing.
If oil has to be added to an engine too often but no leaks are found, the oil is being burned. The most likely
causes of oil burning are worn or broken rings, worn or scored pistons or cylinder walls, loose bearings, worn
intake valve guides or leaking valve seals (intake valves only), and leaking vacuum booster pump diaphragm.
If an engine is burning oil, it usually shows up in the exhaust as smoke. When oil is being burned in the
combustion chamber, the exhaust smoke will have a bluish color. Locating the causes of an engine using too
much oil is described in the lesson on engine inspection and testing.
All of the engines used in the Army's wheeled vehicles are equipped with oil filters. Some use the full-flow
type, while others are equipped with the bypass type. The full-flow filter most commonly used is the
throwaway type.
The oil pressure gages used on the military wheeled vehicles are operated electrically. Procedures for testing
these gages are described in the lesson on wheeled vehicle electrical systems.
All Army wheeled and tracked vehicles use the positive crankcase ventilation system. The air that circulates
through the crankcase enters the engine through a filter on the breather tube or through the air cleaner. In
either case, be sure the filters are clean or that the oil is at the proper level in oil bath filters.
Some engines have a shutoff valve on the air filter in the breather line. Be sure this valve is open at all times
except during fording operations.
Anytime oil is leaking out of the engine by the front or rear crankshaft oil seals, always suspect the crankcase
ventilation system. If the ventilation system is clogged, enough pressure can be built up in the crankcase to
blow the crankshaft oil seals.
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