Lesson 4/Learning Event 3
Learning Event 3:
DESCRIBE MAINTENANCE PROCEDURES FOR ENGINE LUBRICATION SYSTEMS
As an automotive repairer, the major problem you will probably have with the engine lubrication system is oil
leaks. Such leaks are usually visible, so be thorough when looking for oil leaks. When oil leaks are found, look
for the causes. An oil leak is almost certain to develop if things, such as the oil pan bolts or valve cover bolts,
are loose. Oil levels too high and clogged crankcase ventilation systems are other major causes for oil leaks.
Let's go through a step-by-step procedure for checking the lubrication system on an Army truck. The
procedures described here are for the M151 1/4-ton truck, but most of the procedures will apply to any
First, check the level and condition of the oil. If you find the oil level too high, check the level of the coolant
in the radiator. Unless the vehicle driver put too much oil in the crankcase, the most likely cause of a high oil
level is water leaking from the cooling system into the oil.
If the coolant level in the radiator is low, allow the vehicle to sit without the engine running for awhile, and
then remove the oil drain plug slowly. If there is water in the crankcase, it will run out first, because water is
heavier than oil and will settle to the bottom of the oil pan sump. Water from the cooling system usually gets
into the oil pan by a leaking cylinder head gasket.
Of course, if the engine has been running, the oil and water will be mixed. The water may give the oil a milky
color or if the oil is cold it will be sludgy. Oil mixed with water also has a different feel when rubbed with the
fingers than plain oil.
In checking for oil leaks, look for drops of oil on the floor under the engine. Then examine all possible places
the oil may leak out. In addition to such places as the oil pan, timing gear cover, valve pushrod cover, and
valve rocker arm cover gaskets, oil can leak out around the oil filter, vacuum booster pump, oil gage, and any
external oil lines. The crankshaft oil seals can also leak. Oil leakage around the front crankshaft oil seal will
probably be thrown all over the front of the engine by the crankshaft pulley. The fan belts will probably be oil