Lubricants
Every manufacturer recommends the octane rating
of the gasoline considered best for the engines
A lubricant (oil or grease) is a substance used to
produced. In addition to engine design, factors like the
reduce friction by preventing direct contact of moving
weight of the vehicle, the ground and highways over
surfaces with each other. The lubricant is pressed into a
which it is driven, and the climate and altitude of the
thin film between moving parts, which rub on the film.
locality also determine what gasoline is best to use. All
The film of oil gives a slippery nature to surfaces. This
other factors being equal, the following may be
film is constantly renewed by additional oil supplied
considered as some of the properties of the best
from a pressure pump to replace oil forced out by
gasoline:
movement of the engine parts. The effect is two sheets
Good antiknock quality; a minimum content of
or layers of oil sliding over each other. Thus, friction
foreign matter
between the two metal surfaces is reduced to a
A volatility that makes starting easy, allows
minimum.
smooth acceleration, and costs less to operate
In addition to reducing friction and wear, lubricants
act as cooling agents, which absorb heat from the
NOTE: The type of gasoline recommended by the
surfaces over which they are spread. This is very true of
manufacturer should always be used to ensure
engine oil, which carries heat to the engine oil pan
maximum performance.
where it is cooled. On some engines the oil is circulated
DIESEL FUEL.--Diesel fuel is heavier than
through a water-cooled oil cooler to further cool off the
gasoline because it is taken from the residue of the
heat.
crude oil after the more volatile (easily ignited) fuels
Lubricants are also used as sealing agents. They fill
have been removed. As with gasoline, the efficiency of
the tiny openings between moving parts, cushioning
a diesel fuel varies with the type of engine in which it is
them against damage from extreme heat.
a suitable diesel fuel can be obtained for almost all
Lubricants also act as cleaning agents. Grit and dirt
engine operating conditions. Slow-speed diesels use a
that get into engine parts are removed by the lubricants
wide variety of heavy fuels; high-speed diesel engines
before damage results. Foreign matter found in old oils
require a lighter fuel. A poor or improper grade of fuel
and greases in the bottom of the crankcase is evidence
can cause hard starting, incomplete combustion, a
of the cleansing quality of lubricants. In addition, some
smoky exhaust, and engine knocking.
lubricants have chemicals added to make them better
cleaners.
The properties a manufacturer considers in
specifying a fuel for a diesel engine are volatility,
OILS.--The high temperatures, speeds, and
cleanliness, viscosity (consistency), ignition quality,
cylinder pressures of modern engines have made better
and antiknock quality.
grades of lubricating oils necessary. To increase
efficiency, certain chemicals called "additives" are put
JET PROPULSION FUELS (JP).--More often,
into oils. Additives are resistive agents, which are used
jet propulsion fuels (JP) are for use in jet engines.
against oxidation and other kinds of metal decay. Oil
However, some types of jet fuels (such as JP-4 and
that contains additives specifically designed to help
JP-5) are well suited for use in modern, high-speed
clean the piston rings and other parts of the engine as it
diesel engines, such as those used in support
lubricates is known as "detergent oil."
equipment. Most manufacturers specify diesel fuel
(grade DF-1 or DF-2) or jet propulsion fuel (JP-5). The
Lubricating oils serve the following purposes:
selection is dependent upon availability except in the
Prevent metal-to-metal contact in moving parts
case of a gas turbine power unit mounted on a tractor,
of mechanisms
which depends upon the tractor for its fuel supply. To
meet the requirements of the gas turbine power unit,
Help carry heat away from the engine
aviation jet fuel is the type of fuel that must be used.
Clean the engine parts as they are lubricated
Aviation fuels are more useful than diesel fuels because
they provide more power outlet per pound, fewer
Form a seal between moving parts
pollutants, increased engine life, and greater
Moving parts that do not have enough oil melt,
availability aboard naval air stations and aircraft
fuse, or seize after a very short period of engine
carriers.
operation. All gears and accessory drives (as well as
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