What does 5w40 mean on engine oil?
2 Answers
The "5W-40" on engine oil, the "W" stands for "winter", meaning it is for winter use. The number 5 before the "W" represents the viscosity under low-temperature conditions. Here is a related introduction about the selection of engine oil grades: 1. German cars: Start with 0W40/5W40, but some 30-grade oils are also suitable for German cars. Small-displacement German cars can use 30-grade oils that meet the viscosity requirements when new. 2. Domestic, American, Korean, and French cars: Generally, use 0W30/5W30 within 60,000 kilometers, and switch to 0W40/5W40 after 100,000 kilometers. These four types of car engines have relatively consistent characteristics. The grade can be selected based on the displacement. Small-displacement cars (below 1.8L) can use 0W30 grade for a long time, while large-displacement cars (above 2.0L) can switch to 0W40 grade earlier.
Every time I change my car's engine oil, I check the rating on the bottle, like 5W40. That's the oil viscosity, right? The 5W refers to winter low-temperature performance—the lower the number, the better. A 5 means it can still flow quickly at temperatures below -30°C, ensuring fast lubrication during startup. The 40 indicates viscosity at high temperatures—the higher the number, the thicker the oil, which helps maintain a protective layer when the engine heats up. 5W40 oil is quite versatile, suitable for year-round use, especially in cold northern regions or for cars that frequently drive on highways. My car has been running smoothly for years with good fuel efficiency, though I check it more often during extremely hot summers. Don’t pick the wrong grade—stick to the manual’s recommendation and avoid switching arbitrarily, as the wrong oil could lead to burning oil or engine wear. In short, these numbers may seem simple, but they’re crucial for your car’s health. Regular oil changes help prevent issues.
