What is the model number of all-season engine oil?

All-season engine oil models include 5W-20, 5W-30, 5W-40, 5W-50, 10W-20, 10W-30, 10W-40, 10W-50, 15W-20, 15W-30, 15W-40, 15W-50, 20W-20, 20W-30, 20W-40, 20W-50, and so on.

In engine oil model numbers, the symbol W stands for Winter. The smaller the number before W, the lower the low-temperature viscosity, the better the low-temperature fluidity, and the lower the applicable minimum temperature. The larger the number after W, the higher the viscosity and the higher the applicable maximum temperature. In addition to all-season oil, there is also summer oil and winter oil. Winter oil grades are 0W, 5W, 10W, 15W, 20W, and 25W, while summer oil grades are 20, 30, 40, and 50.

The oil grade follows the internationally unified API standard, so we can also see letters like SN or SM before the oil model number. S stands for gasoline engines, while C stands for diesel engines. The performance grade of oil is ranked starting from A, currently up to N, so SN is the highest-quality oil standard.

Additionally, engine oils are categorized into mineral oil, semi-synthetic oil, and full-synthetic oil, with the main difference being their service life. Among them, mineral oil has the shortest service life, requiring an oil change every 5,000 kilometers or 6 months for engines using mineral oil. Semi-synthetic oil lasts slightly longer than mineral oil, needing replacement every 7,500 kilometers or 9 months. Full-synthetic oil has the longest service life, requiring replacement only every 10,000 kilometers or 12 months. However, full-synthetic oil is correspondingly more expensive, semi-synthetic oil is mid-priced, and mineral oil is the cheapest.

The model number of all-season engine oil typically follows the SAE viscosity grading system, such as 5W-30 or 10W-40. The "W" stands for winter, indicating cold-weather performance, while the second number represents viscosity at operating temperature. For most modern cars in temperate climates like Britain, 5W-30 is a common recommendation, balancing cold starts and high-temperature protection.

1. 5W-30: Ideal for petrol and diesel engines in moderate climates, offering good fuel efficiency and cold-start performance. Used in models like the Ford Focus or Vauxhall Corsa.
2. 10W-40: Better suited for older engines or high-mileage vehicles, providing thicker lubrication under heat stress.
3. 0W-20: Often specified for newer hybrids or efficient petrol engines (e.g., Toyota Prius), optimised for low friction.

Always check your vehicle’s manual or use online tools from brands like Castrol or Shell to confirm the correct grade. Using the wrong oil can affect engine longevity and fuel economy.

From a mechanic’s perspective: Stick to the manufacturer’s specified oil grade, usually found in the handbook or under the bonnet. For all-season use, 5W-30 covers most modern engines, while classics might need 20W-50. Avoid generic "all-purpose" oils—precision matters. A misgraded oil can cause premature wear, especially in turbocharged engines like those in a BMW iX.