(1) Lubrication:
The engine is running, if some of the friction parts deprived of proper lubrication, it will produce a dry friction. Practice has proved that the heat generated by the dry friction in a short time enough to make the metal melt, resulting in damage to the parts of even stuck the (many leaks or oil spills car cylinder, axle failure, the main reason for this). It is necessary to give good lubrication of the friction parts in the engine. Lubricant flow to the friction parts, adhesion in the friction surface, the formation of a layer of film to reduce friction between the parts of the resistance of oil film strength and toughness is the key to play the role of lubrication.

(2) The cooling effect:
Fuel combustion in the engine after the heat generated, only a small portion of the power output as well as the frictional resistance of consumption and the driver of the subsidiary bodies; most of the remaining heat in addition with the exhaust gas discharged to the atmosphere and foreign, but also with the cooling medium in the engine go part of. Excess heat in the engine must be eliminated from the body, otherwise the engine temperature is too high and burned. This regard by the engine cooling system to complete the other hand rely on the lubricant to absorb heat from the surface of the cylinder, piston, crankshaft, oil pan and brought to dissemination.

(3) Washing the role of:
Engine work, it will generate a lot of dirt. Such as inhalation of colloidal material generated in the sand in the air, dust, coke formation in the combustion of the mixture, lubricant oxidation, mechanical friction between the metal shavings, and so on. These contaminants will be attached to the mechanical friction on the surface if not cleaned off, it will increase the mechanical wear. In addition, a large number of glial make piston rings bonded card stagnation, causing the engine can not operate normally. Therefore, we must promptly these dirt cleaning, this cleaning process is to rely on lubricants to complete the circular flow of the body.

(4) Sealing effect:
There is a certain gap between the engine cylinder and piston, piston ring and ring groove and the valve and valve seat, this will ensure not catching among the deputy campaign. However, these gaps can cause the cylinder sealed well, the combustion chamber leak is to reduce the cylinder pressure and engine output, film lubricant in these gaps, to ensure the tightness of the cylinder to maintain cylinder pressure and engine output, and to prevent the exhaust gas down into the crankcase.

(5) Rust-proof role:
Engine operation or storage, the moisture in the air, lubricating oil, fuel and combustion acid gas, the parts will cause corrosion and rust, thereby increasing the damage to the friction surface, direct contact with oil in the parts of the surface film to avoid parts with water and acid gases to prevent corrosion, rust.

(6) To eliminate the impact of:
Load at the end of the compression stroke, the mixture starts to burn, a sharp rise in cylinder pressure. At this time, the lubricant in the bearing clearance will ease the piston, piston pin, connecting rod, crankshaft and other parts by the impact load, the engine smooth and to prevent direct contact with the metal, reducing wear.