Symbol 3080, for example, shows that the oil is
means a flatter slope, or lesser variation of
a 3000 series oil and that a 60-ml sample should
viscosity with the same changes in temperatures.
flow through a standard orifice in 80 seconds
If you are using an oil with a high viscosity
when the oil is at a certain temperature (210F,
index, its viscosity or body will change less when
in this instance). Another example is symbol
the temperature of the engine increases.
2135 TH. This symbol shows that the oil is a 2000
series oil and that a 60-ml sample should flow
Pour point--The pour point of an oil is
through a standard orifice in 135 seconds when
the lowest temperature at which the oil will barely
the oil is at a certain temperature (130F, in this
flow from a container. At a temperature below
case). The letters H, T, TH, or TEP added to a
the pour point, oil congeals or solidifies. Lube oil
basic number indicate a primary specific use
used in cold weather operations must have a low
within the general category. In this case it indicates
pour point. (NOTE: The pour point is closely
the oil contains additives for special purposes.
related to the viscosity of the oil. In general, an
oil of high viscosity will have a higher pour point
Properties of Lube Oils
than an oil of low viscosity.)
Lube oils used by the Navy are tested for
Flash point--The flash point of an oil is
several properties. These include viscosity, pour
the temperature at which enough vapor is given
point, flash point, fire point, autoignition point,
off to flash when a flame or spark is present. The
neutralization number, demulsibility, and
minimum flash points allowed for Navy LO are
precipitation number. Standard test methods are
all above 300F, and the temperatures of the oils
used for each test. The properties of LO are
are always far below that under normal operating
briefly explained in the following paragraphs.
conditions.
Viscosity--The viscosity of an oil is its
Fire point--The fire point of an oil is the
tendency to resist flow or change of shape. A
temperature at which the oil will continue to burn
liquid of high viscosity flows very slowly. In
when ignited.
variable climates, for example, automobile owners
change oil according to the seasons. Oil changes
Autoignition point--The autoignition
are necessary because heavy oil becomes too thick
point of an oil is the temperature at which the
in cold weather, and light oil becomes too thin
flammable vapors given off from the oil will burn
in hot weather. The higher the temperature of an
without the application of a spark or flame. For
oil, the lower its viscosity becomes; lowering the
most LO, this temperature is in the range of
temperature increases the viscosity. On a cold
464 to 815F.
morning, the high viscosity or stiffness of the LO
makes an automobile engine difficult to start. The
Neutralization number--The neutralization
viscosity must always be high enough to keep a
number of an oil indicates its acid content. It is
good oil film between the moving parts; other-
defined as the number of milligrams of potassium
wise friction will increase, resulting in power loss
hydroxide (KOH) required to neutralize 1 gram
and rapid wear on the parts.
of the oil. All petroleum products deteriorate
(oxidize) in the presence of air and heat; the
Oils are graded by their viscosities at certain
products of this oxidation include organic acids.
temperatures. The grade is determined by the
If organic acids are present in sufficient
number of seconds required for a given quantity
concentration, they have harmful effects on alloy
(60 ml) of the oil at the given temperature to flow
bearings at high temperatures, on galvanized
through a standard orifice. The right grade of oil,
surfaces, and on the demulsibility of the oil with
therefore, means oil of the proper viscosity.
respect to fresh water and seawater. This last
Every oil has a viscosity index based on the
effect, in turbine installations, may result in the
slope of the temperature-viscosity curve. The slope
formation of sludge and emulsions too stable to
be broken by the means available. An increase
of the curve is based on the rate of change in
viscosity of a given oil with a change in
in acidity is an indication that the LO is
temperature, but with other conditions remaining
deteriorating.
unchanged. A low index figure means a steep
slope of the curve, or a great variation of viscosity
Demulsibility--The demulsibility, or emulsion
property, of an oil is its ability to separate cleanly
with a change in temperature; a high index figure
4-3
