Page 153 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

ii Viscosity: A measure of the internal resistance of a lubricant is called its viscosity. This is an important property
of lubricating oils, as viscosity determines the oil’s ability to flow. If a substance flows easily, its viscosity is low.
Conversely, if a liquid flow with difficulty, its viscosity is high. A viscometer is used to determine the viscosity
of the lubricant to be tested. This quality of lubricants is expressed by numbers. This number is given by the
Society of Automotive Engineers (SAE). The table below shows the different types of lubricating oils along with
their viscosity numbers and applications.
Table

Expected Single Viscosity Lubricant Multi-Viscosity Lubricants
Atmospheric Temperature
Below -10°F SAE 5W SAEFW-20

Above -10°F SAE 10W SAE10W-20 OR SAE10W-30

Above +10°F SAE 20W SAE20W-30 OR SAE10W-30
Above 32°F SAE 20 or 20W SAE10W-20 OR SAE10W-30
SAE 30 (some manufacturers)

Above 90°F SAE 30 SAE10W-20 OR SAE10W-30
SAE 30 (some manufacturers)
iii Fire and Flash Point: For a lubricant, the temperature at which it ignites in the form of a flame is called the
flash point. Similarly, for a lubricant, the temperature at which it begins to vaporize is called the flash point.
While selecting the lubricant it is necessary to keep in mind that the operating temperature of the machine
should be less than the flash point and combustion point of the lubricant.
iv Pour Point: Pour point is the lowest temperature at which an oil can flow or be dropped. Pour point is an
important specification for lubricants used in machines operating at low temperatures; Like- there were ice
factories, refrigerators etc. A good lubricant should have a low pour point so that it can work smoothly even at
low temperatures.
v Carbon Residue Content: The amount of residual carbon powder in an oil indicates its amount of waste
material and its lubricity. In order to achieve high efficiency of an engine, the amount of residual carbon in the
lubricating oil used in it should be minimum. For internal combustion engines and compressors, this amount is
even more essential.

vi Acidity: The oil should not contain acidity or acid content, if it does, it will adversely affect the bearing metal.
vii Emulsification and Distinctively of Water: Miscibility is the property of a lubricating oil, due to which it can
mix rapidly with the gel and form a uniform and almost permanent mixture. Similarly, water-separation is the
property of a lubricating oil due to which water can be quickly separated from the water-oil mixture.
viii Specific Gravity: It is the property of the lubricant that compares the load of the lubricant with the load of the
leaves at 30°F.

ix Neutralisation Number: The neutralization number is the amount in milligrams of potassium hydroxide that
can be dissolved in one gram of lubricating oil.
The neutralization number has no significant relationship with the acidity present in the lubricating oil. The
main thing is that during the use of lubricating oil, the depression should not increase. A sudden increase in its
value means that the oil is oxidized (oxidise).

This number is less than 0.01 in well-cleaned lubricating oil. If this number starts to increase suddenly in a
working machine, the oil should be taken out and new oil should be added.
x Chemical stability: Chemical stability is the characteristic of lubricating oils, due to which they are adopted.
They maintain organization and existence and do not disintegrate under the influence of work.
Types of lubrication systems
Wet Sump Lubrication System: In Method
Oil is stored in the sump. or oil contacts the sump or crankcase.it is of the following points

140
CITS : Automotive - Mechanic Diesel - Lesson 39 - 46