The primary objective of the lubricant is reduction of friction caused between moving parts of engine. This in turn helps to increase life of the engine. Specialized lubricants such as hydraulic or transmission oils perform additional functions. Lubricants are also used as coolants, to reduce the heat that is produced by the engine.
Reduces Friction ________________________________________________________________
This result in reduction of energy required to operate the mechanism and also reduces local heat generation. It forms a fluid film that keeps one moving surface out of direct contact with the opposing surface.
Reduces Wear & Tear ____________________________________________________________
Additives in the lubricants lay down a chemical film that protects wear and tear. Oil additives that reduce friction contribute to the energy efficiency of the vehicle.
Cooling of Engine _______________________________________________________________
Lubricants work as an initial heat transfer agent in engine between some parts heated by combustion and the heat dissipating systems. Lubricants reduce heat generated by friction or the mechanical work performed. Circulation of the lubricant transfer heat away from hot surfaces, warms cold surfaces, and transports debris and contaminants to the filter.
Anti-corrosion __________________________________________________________________
Oil can become acidic and corrode metals because of its own degradation or by combustion contamination. Moist environments and lack of use can also cause rusting. Lubricants act as anti-corrosion agents and prevent any degradation.
Cleaning _______________________________________________________________________
Deposits such as “solid carbon”, “varnish”, or “sludge” can interfere with the correct and efficient operation of the equipment. Piston rings may become stuck and oil passages get blocked. Lubricants can prevent this by improving viscosity control of oils.
Sealing ________________________________________________________________________
Lubricants assist in forming seals between pistons and cylinders. High-quality oils can provide increased bearing protection.
Help Save Costs ________________________________________________________________
Good quality lubricants reduces drain interval of oil which leads to savings of costs in terms of material, labor and equipment downtime.
DIFFERENT GRADES OF OIL
Choosing the proper viscosity grade for the ambient temperature of your geographic location becomes vitally important.
To lubricate and provide protection to the engine and improving its performance, the viscosity (the measure of the Oil’s thickness or resistance to flow) of the engine oil should be capable of holding up the engine’s extreme temperature conditions. Oil thins when heated and thickens when cooled.
There are mono-grade oils whose viscosity is defined at only one temperature, either high or low. A multi-grade meets both high and low temperature viscosity requirements simultaneously. These are easily recognized by dual viscosity designations like 15W40, 10W30 etc. For instance in case of 15W40, 15W is the low temperature designation and the 40 is the high temperature designation.
It is the viscosity modifier additive that produces a thickening effect at high temperatures but is dormant at low temperatures.
CHOOSING THE RIGHT GRADE
The vehicle handbook generally specifies the right grade of oil for the car under specific environmental conditions

Viscosity Grade	Temperature Conditions	Descriptions
5W-30	Below 0°F	Mostly used in the ultra modern automobile models Excellent fuel economy Low temperature performance
10W-30	Above 0°F	Most frequently recommended for most automobile   engines like high-performance multi-valve engines   and turbo-charged engines
10W-40	Above 0°F	For controlling engine wear and tear For preventing oil breakdown from oxidation
20W-50	Above 20°F	For maximum protection for high-performance, high-   RPM racing engines. Very good choice for high temperature and heavy   loads, e.g. driving in the desert or towing a trailer   at high speeds for long periods.
SAE 30	Above 40°F	For cars and light trucks
SAE 40	Above 60°F	Not recommended when cold-temperature starting   is required