Engine Oil Functions
 Modern
engines are capable of giving good service for several hundred thousand
miles. However, such reliable service is dependent on the care given to
the engine. The most basic care is the quality of engine oil used and
the frequency with which it is changed. The most severe kind of driving
for the engine is short-trip driving of less than 15 miles at a time.
This is, by far, the most typical service for the average driver. Short-trip
use of the engine requires better oil performance levels and more frequent
oil changes
Oil performs many functions within the engine. In addition to its primary
task as a lubricant by controlling wear and oxidation, the oil also serves the
engine by cooling, cleaning, sealing, and inhibiting corrosion.
• As a lubricant, oil must maintain a protective
film to prevent metal-to-metal contact. It must be fluid enough to allow easy
starting and to circulate quickly through the engine, yet remain thick enough
at higher operating temperatures and speeds to provide adequate lubrication.
• As a coolant, oil carries off about 40% of the heat
that's generated by the operating engine. Once the engine is fully warmed
up, the circulating oil can encounter temperatures of 300°F or higher
in severe service.
• As a detergent, engine oil must be able to gather
and suspend dirt and other contaminants until the oil can leave them as it
passes through the filter and returns to the internal engine environment.
The oil must also be able to tolerate accumulation of moisture, gasoline,
and other contaminants in short trip driving without forming deposits or sludge.
• As a sealer, oil coats the cylinder walls and fills
in the microscopic pores and gaps that would otherwise allow compression to
blow past the rings (called blow-by). It also interacts with gaskets and seals
to cause them to slightly swell, thus preventing oil leaks and maintaining
oil pressure.
• As a corrosion inhibitor, oil coats internal engine
parts to prevent surface rust on the inside of the engine which can be caused
by blow-by products and water formed in combustion. It must also be capable
of neutralizing the acids that are formed by combustion blow-by and oil oxidation
at high temperatures.
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