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TM 9-8000
Figure 8-2. How Oil Lubricates
drop In its lubricating qualities. Some of the causes of oil
mostat (para 9-9) or an engine that Is operated for short
dilution are the following.
durations only will never reach a sufficient temperature to
burn the fuel completely. A small amount of oil dilution
(1) Excessive use of a hand choke causes an
occurs in all engines from initial startup through warmup.
overrich mixture and an abundance of unburned fuel to
When the engine reaches its operational range (180F
leak past the piston rings Into the crankcase. The same
(82.2C) to 200F (93.3C)), however, this condition is
condition can occur on vehicles equipped with an
corrected as the excess gasoline vaporizes In the
Improperly adjusted or malfunctioning automatic choke
crankcase and is carried off by the crankcase ventilation
American Petroleum Institute (API) Rating
(2) A vehicle with a defective ignition system
can cause oil dilution due to misfiring spark plugs.
Whenever a spark plug misfires, the balance of the
a. General. The API system for rating oil classifies
unburned fuel will be forced into the exhaust system but
oil according to its performance characteristics.  The
a small portion of it also will pass the rings and enter the
higher rated oils contain additives that provide maximum
protection against
(3) An engine with a malfunctioning ther-


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