What is the difference between 5W-30 and 5W-40?
2 Answers
The main difference between 5W-30 and 5W-40 lies in their viscosity. The number following the 'W' indicates the kinematic viscosity of the oil at 100°C. A higher number means the oil has higher viscosity, so 5W-30 oil has slightly lower viscosity than 5W-40. Additionally, their stability at high temperatures differs. 5W-40 offers better high-temperature stability compared to 5W-30. W stands for 'winter,' and the smaller the number before it, the better the oil's low-temperature fluidity. This means the oil can be used in lower environmental temperatures and provides better engine protection during cold starts. The number before the W represents the freezing point: 0W is -35°C, 5W is -30°C, 10W is -25°C, 15W is -20°C, 20W is -15°C, and 25W is -10°C. The number after the W indicates the oil's kinematic viscosity at 100°C. A higher number means higher viscosity and better protection at high temperatures. It can also be understood as representing the oil's stability at high temperatures (i.e., its resistance to thinning). A larger number indicates better high-temperature stability. 5W-30 oil is less viscous than 5W-40, making it more suitable for new engines and vehicles. 5W-40 oil has higher viscosity, making it more suitable for older vehicles as it enhances sealing and helps prevent oil consumption. However, in practice, the difference between the two is minimal. Both 5W-30 and 5W-40 have a wide temperature range and are considered all-season oils, providing good fluidity for cold starts and a thicker oil film at high temperatures for better engine protection. Under the high-speed, high-temperature, and high-pressure conditions of engine operation, oil needs to be replaced regularly. The replacement interval varies depending on the oil quality. After reaching the replacement interval, the vehicle can still be used, but the oil should be replaced as soon as possible. Typically, fully synthetic oil should be replaced every 8,000 to 10,000 kilometers. During the warranty period required by the vehicle manufacturer, failure to perform timely maintenance may result in engine issues and affect the vehicle's warranty. Expired oil can negatively impact engine performance. Over time, oil can oxidize and absorb moisture, leading to degradation and reduced performance. To ensure timely oil changes, many manufacturers now include maintenance reminder lights or notifications in their vehicles. These alerts inform the owner when it's time to replace the oil and oil filter based on mileage or time intervals.
I've been driving my small sedan to and from work, usually using 5W-30 oil. It feels particularly smooth when starting in cold weather, with lower viscosity at low temperatures, making the engine easier to start and relatively more fuel-efficient. On the other hand, 5W-40 is thicker in high-temperature environments, such as during long-distance summer trips, providing better engine protection and reducing wear. However, if used in a new car that recommends 5W-30, it can increase fuel consumption and may even cause oil pressure issues. The most important thing is to check your vehicle's manual, as different models have different requirements. Older cars or those in hot climates are better suited for 5W-40, while 5W-30 is cost-effective for regular city driving. Don't randomly choose oil grades during regular oil changes—using the wrong one could shorten engine life and affect the overall driving experience.
