Learn the fundamentals about Lubrication oil and Grease (automobile engineering)

1. Lubrication Oil

The reason for lubricating each part of the engine is to reduce friction, prevent power loss and increase engine efficiency while preventing wear and damage.

Type of engine oil

Engine oil is mainly a heavy oil made from a mixture of green, translucent hydrocarbons distilled from crude oil.

a. Viscosity

• Although there are many properties required of lubrication oil, the most important one is viscosity.
• Viscosity is the measure of the oil's degree of stickiness, and an oil with a high viscosity provides a thick oil film on metal surfaces and has the power to consequently support large loads.
• However, if the viscosity is too high, the internal friction of the lubrication oil increases, causing resistance and power loss to increase.
• Conversely, if viscosity is low, power loss is low, but the oil film breaks down and the friction reduction performance is inadequate.
• The most important problem concerning the viscosity of lubrication oil is temperature. In general, the viscosity of lubrication oil decreases as the temperature increases. This extent of viscosity change in relation to the temperature is called the viscosity index.

b. Viscosity category (SAE standard) 

• For viscosity categories, generally the SAE (the USA Society of Automotive Engineers) standard is used. 
• The SAE number is applied in accordance with the normal ambient temperature as shown in the diagram. The oil usage category is not determined just by the usage temperature, but also by the vehicle driving conditions.
• The lower the viscosity number, the lower the oil viscosity. Oil with a viscosity number that indicates a range such as 10W-30, 20W-40 is called
• It exhibits little viscosity change with temperature so it is not necessary to start or stop using it in accordance with the season. Numbers that include W (winter) indicate a viscosity range as far as -17.8 °C (0 °F), and numbers without W have a viscosity range up to 98.9°C (210 °F).

Centigrade C 5/9(F-32) Fahrenheit F= 9/5xC+32

c. Category according to performance or application (API service category)

• For categories in accordance with performance or application, the API (American Petroleum Industry) service categories are generally used.

i) For gasoline engines

a) SD

⚫ Used for engine operating in low temperature, high temperature operation and severe conditions. Detergent dispersant, anti-friction substances and an oxidants, etc. are added.

b) SE

⚫ Used for engines subject to more severe conditions than the SD class. A large quantity of detergent dispersant, wear prevention substances and anti-oxidants etc. are added.

c) SF

⚫A high quality oil which provides superior valve system wear resistance and durability than SE.

d) SG

⚫ A top grade oil that provides superior high temperature anti-oxidation and valve system wear resistance than SF.

d. Category according to base material (mineral, vegetable, chemical synthetic, semi-synthetic)

i) Mineral type (engine oil, gear oil, spindle oil, machine oil, etc.)

• This includes petroleum based products extending over a wide range from inexpensive products up to racing oil. The majority of engine oils are included.

ii) Vegetable type (castor oil, etc)

• Based on oils such as castor oil, they provide excellent lubrication so they are mainly used in racing. Compared with mineral oils, oxidation proceeds rapidly after exposure to external air, so they cannot withstand long term use and are not suitable for general use.

iii) Chemical synthetic type (silicon oil, ester type oil, etc.)

• These oils were developed to maintain stable viscosity from high temperatures to low temperatures. The base materials are petroleum products such as ethylene which are broken down and chemically processed into the ideal molecular construction.
•  Adjustment as desired provides performance suited to the purpose, providing high lubrication performance and anti-oxidation performance, so that the oi characteristics cover the properties supplemented by the addition of anti-oxidants and viscosity-enhancing agents in traditional oils, and provide stable high performance.

iv) Semi synthetic type

• These are oils composed of a blend of chemically synthesized oils, mineral oils and vegetable oils. They provide the stable characteristics of chemically synthesized oils and the good characteristics of mineral and vegetable oils.

2. Grease

Grease is produced by mixing mineral oils and metallic soap. Although at normal temperatures it is in a soft semi-solid state, when riding starts the friction heat gradually softens it and it forms an oil film on the friction surfaces to function as a lubrication oil. When riding stops, it returns to its original semi-solid condition. 

Grease used in gasoline engines includes the following types.

1) Calcium soap grease (chassis grease, etc.)

⚫ Calcium soap grease is used for water pumps, etc. Its primary feature is its water resistant performance and its heat resistance so that it is not flushed away even when the coolant temperature gets hot.

2) Lithium soap grease (bearing grease, rubber grease, etc.)

⚫ Lithium soap grease is used for generator bearings, swing arm, steering bearing. clutch lever pivot shaft, shift pedal pivot shaft, center stand and side stand etc. Its is used as a low viscosity mineral oil with heat resistance and mechanical stability suited to high engine speeds. This grease has good water resistance and cold resistance and is also called a multi-purpose grease.