What Does the Engine Oil Number Mean?

[VonEden]

Engine oil grades consist of two parts: classification and viscosity specification. The viscosity of lubricating oil is often indicated by SAE grades, where SAE stands for the "Society of Automotive Engineers." Engine oil grades: For example, in "15W-40" or "5W-40," the "W" stands for Winter. The smaller the number before "W," the better the oil's low-temperature fluidity, indicating it can be used in lower environmental temperatures and provides better engine protection during cold starts. The number after "W" represents the oil's kinematic viscosity at 100°C, with higher numbers indicating higher viscosity. For instance, 40 means the kinematic viscosity standard at 100°C is between 12.5mm²/s and 16.3mm²/s. Engine oil grades are specifically categorized into 4 types for summer, 6 types for winter, and 16 types for all-season use. Summer oils are labeled as 20, 30, 40, and 50, where larger numbers indicate higher viscosity and suitability for higher temperatures. Winter oils are labeled as 0W, 5W, 10W, 15W, 20W, and 25W, with "W" representing Winter. The smaller the number before "W," the lower the low-temperature viscosity and the better the low-temperature fluidity, making it suitable for lower temperatures. All-season oils are labeled as 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, and 20W/50. Here, the smaller the winter number, the better the low-temperature performance, and the larger the summer number, the higher the viscosity, resulting in a broader applicable temperature range.

[SanCarter]

I used to be a long-time driver and am very familiar with engine oil grades. It's that string of numbers printed on your oil can, like 5W-30 or 10W-40. These aren't just random numbers—they indicate the oil's flow characteristics at different temperatures. The letter 'W' with the preceding number, such as 5W, refers to the oil's viscosity during cold winter starts. The smaller the number, the thinner the oil, allowing it to flow faster during cold starts and reduce engine wear. The number without the 'W,' like 30 or 40, represents the oil's viscosity at high summer temperatures. A higher number means thicker oil, which provides better engine protection. Choosing the right grade is crucial. I remember my neighbor mistakenly used 10W-40 in a car that required 5W-30, resulting in louder engine noise and increased fuel consumption. Eventually, the car had to be sent for repairs, costing both time and money. Newer cars typically use 0W-20 for better fuel efficiency, while older cars benefit from higher viscosity oils like 5W-40 to prevent wear. Always follow your car's manual recommendations and avoid making arbitrary changes. Regular oil changes can significantly extend your engine's lifespan.

[Alexa]

As a car enthusiast who loves studying technical details, I find the oil viscosity grades like 5W-30, which are set according to SAE standards, quite fascinating. The first part, 5W, indicates low-temperature viscosity - the smaller the number, the more fluid the oil is, enabling quick engine starts in cold winters and reducing friction damage. The latter part, 30, represents high-temperature viscosity - the larger the number, the stronger the oil film, which resists high-temperature pressure and protects internal components. Choosing the wrong grade can slow engine response and even increase fuel consumption. I once tried lower viscosity oil in an old car and felt smoother acceleration, but you must ensure it matches the manual. There's also the difference between synthetic and mineral oils - synthetic oils maintain stable viscosity grades and perform better under extreme temperature variations, though they cost more. Avoid mixing oil types to prevent chemical reactions that could degrade quality. Don't exceed the manufacturer's recommended oil change interval of around 5,000 km - being too lazy about this can harm your engine.

[Stephen]

In the repair shop, I often help people check common oil grade issues like 5W-30. The first number 5W indicates cold-start viscosity - the smaller this number, the faster the engine starts. The latter number 30 represents high-temperature viscosity - the larger this value, the better the protection. Using the wrong grade can cause engine wear, increased noise, or higher fuel consumption. When changing oil, select the grade based on your vehicle's age and local climate. Use higher viscosity oils in hot southern regions, and lower viscosity in cold northern areas. Synthetic oils last longer but still require regular changes. Don't cut costs with off-brand products, or you might face major engine repairs later.