How to Choose Engine Oil? A Detailed Selection Guide

Selecting engine oil primarily involves considering its classification, specifications, and brand. Generally, the choice should be tailored to the specific vehicle model.

I. Classification of Engine Oil

1. By Composition

• Mineral Oil:
  Made from petroleum-based mineral oil blended with additives. It is affordable but less durable, requiring more frequent maintenance. Often used in economical vehicles, such as budget cars or vans.

• Semi-Synthetic Oil:
  Blended from 40% mineral oil and 60% fully synthetic oil (by volume). It costs slightly more than mineral oil and serves as an ideal transition product between mineral and full synthetic oils. Recommended replacement interval: every 6 months or 7,500 km.

• Fully Synthetic Oil:
  A premium-grade oil chemically synthesized from crude oil. It boasts the longest performance lifespan, with a recommended replacement interval of 1 year or 10,000 km. Though pricier than semi-synthetic oil, its extended durability justifies the cost.

2. By Specification

• Winter Oils:
  Denoted by grades like 0W, 5W, 10W, 15W, 20W, 25W (where "W" stands for "Winter"). The smaller the number before "W," the lower the low-temperature viscosity and the better the cold-weather fluidity. These oils are designed for regions with harsh winters.

• Summer Oils:
  Graded as 20, 30, 40, 50. The higher the number, the greater the viscosity and heat resistance, making them suitable for high-temperature summer conditions.

• All-Season Oils:
  Examples include 5W-20, 5W-30, 5W-40, 10W-30, etc. These combine winter and summer performance: the smaller the winter-grade number and the larger the summer-grade number, the wider the temperature range they can handle.

II. Selection Tips

1. Engine Type

• Turbocharged Engines: Opt for fully synthetic or semi-synthetic oil to withstand higher operating pressures and temperatures.
• Naturally Aspirated Engines: Semi-synthetic or mineral oil is generally sufficient.

2. Specification Matching

Choose oil based on local temperature, driving habits, mileage, engine type (diesel/gasoline), and required viscosity.

3. Displacement Consideration

• Smaller Engines: Semi-synthetic oil is usually adequate.
• Larger Engines: Fully synthetic oil is recommended for enhanced protection.

4. Vehicle-Specific Guidelines

Always refer to the owner’s manual for the manufacturer’s specified oil grade, as requirements vary by engine design, vehicle age, and model.

III. Key Knowledge

1. Functions of Engine Oil

Oil performs six critical roles in an engine:

• Lubrication and wear reduction
• Auxiliary cooling
• Sealing and leak prevention
• Cleaning (removing contaminants)
• Rust and corrosion inhibition
• Vibration damping

2. Maintenance Notes

• Quality Check: Regularly inspect oil condition. Replace immediately if it appears deteriorated, darkened, or emulsified.
• Replacement Interval: Typically 5,000–10,000 km, but adjust based on driving conditions (e.g., frequent stop-and-go traffic shortens intervals), oil type, and season.
• Storage: Seal unused oil tightly to avoid contamination and oxidation. Store in a cool, dark place away from direct sunlight and high temperatures to preserve performance.

IV. Conclusion

If you don’t service your vehicle at a 4S store and prefer DIY or independent garage maintenance, mainstream large-brand universal fully synthetic or semi-synthetic oils are reliable choices. Always select oils with viscosity and specifications matching your local climate (extreme highs/lows) to ensure convenience and peace of mind.