All About Engine Oil: Your Car's Life Blood

Engine oil, also known as engine lubricating oil, is hailed as the blood of the car, capable of acting as a lubricant, cleaner, coolant, sealant, and wear reducer for the engine.

Classification of Engine Oil

Based on different base oils, it can be simply divided into mineral oil and synthetic oil (vegetable oil is excluded due to its sparse production). Synthetic oil is further divided into fully synthetic and semi-synthetic. Fully synthetic engine oil is the highest grade.

The key difference between the two is: synthetic oil is applicable at a broader temperature range, has a longer service life, and also costs more. For the same oil film requirements, synthetic oil can achieve it with a lighter viscosity, while mineral oil needs a viscosity relative to synthetic oil to meet the same requirements. In the same working environment, synthetic oil has a longer service life than mineral oil, hence it costs more, but the cost is not much higher than mineral oil when compared to the number of oil changes.

Grading of Engine Oil

Series starting with 'S' represent gasoline engine oil, with standards such as SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL.

Series starting with 'C' represent diesel engine oil, with standards such as CA, CB, CC, CD, CE, CF, CF-2, CF-4, CG-4, CH-4, CI-4.

If both 'S' and 'C' letters are present, it indicates the oil is universal for both gasoline/diesel use.

Grades from SA to SL, with each advanced letter, the performance of the oil will improve than the previous one. The oil will have more additives to protect the engine. The further behind the letter, the higher the quality grade. International brands often have oil grades above the SF level.

Numbering of Engine Oil

The viscosity of lubricating oil is often marked with SAE (Society of Automotive Engineers) grade. For example: SAE15W-40, SAE5W-40. 'W' stands for winter. The smaller the number in front of it, the better the low-temperature fluidity of the oil, which means it can be used in lower ambient temperature, and can provide better protection for the engine during cold start. The number behind 'W' (after the hyphen) is an indicator of the oil's resistance to high temperatures. The bigger the number, the better the oil's protective performance under high temperatures.

(SAE) applicable environment temperature (°C)

5w resists external low temperature -30°C

10w resists external low temperature -25°C

15w resists external low temperature -20°C

20w resists external low temperature -15°C

30 resists external high temperature 30°C

40 resists external high temperature 40°C

50 resists external high temperature 50°C

Function of Engine Oil

1. Lubrication and wear reduction: there is rapid relative sliding between the piston and the cylinder, and the main shaft and the bearing. To prevent excessive wear of the components, an oil film needs to be established between the two sliding surfaces. An oil film of sufficient thickness separates the surfaces of the sliding parts, thereby reducing wear.

2. Rust and corrosion prevention: Lubricating oil can absorb on the surface of the parts to prevent water, air, acidic substances, and harmful gases from contacting the parts.

3. Sealing and leakage prevention: Engine oil can form a seal ring between the piston ring and the piston to reduce gas leakage and prevent the ingress of external pollutants.

4. Cooling: Engine oil can take the heat back to the oil tank and then dissipate it into the air to assist the water tank in cooling the engine.

5. Vibration buffering: When the pressure at the engine cylinder mouth rises sharply, it suddenly intensifies the load on the piston, piston pit, connecting rod and crankshaft bearing. This load is transmitted through the bearing lubrication and plays a buffer effect on the impact load.

6. Cleaning: Good engine oil can carry carbonized substances, sludge, and worn metal particles on engine parts back to the oil tank. Through the flow of the lubricating oil, the dirt on the working surface of the parts is washed away.