What is the difference between synthetic engine oils 5w30 and 5w40?
3 Answers
The difference between fully synthetic engine oils 5w30 and 5w40 is: 5w40 offers better protection at high temperatures compared to 5w30. The smaller the number before the 'W', the lower the viscosity at low temperatures, the better the low-temperature fluidity, and the lower the applicable minimum temperature. The larger the number after the 'W', the higher the viscosity of the oil. The number after 'W' mainly refers to the oil's high-temperature resistance index; the larger the number, the better the oil's protective performance at high temperatures. 5w40 provides better high-temperature protection than 5w30. Below are detailed guidelines for selecting engine oil for cars: 1. Based on vehicle age: Generally, while referring to the vehicle's maintenance manual, new cars should choose oil with slightly lower viscosity. As the vehicle ages, choose oil with slightly higher viscosity. Older car engines experience more severe wear, thus requiring relatively higher viscosity oil for smoother and more comfortable driving. 2. Based on road conditions: Road conditions can significantly affect the lifespan of the oil. In areas with poor road conditions, the oil change interval should be shortened. In urban areas where traffic congestion is frequent, leading to frequent stops while driving, it is recommended to use oil with lower viscosity. If you frequently drive long distances or on highways, it is advisable to use oil with slightly higher viscosity.
The difference between synthetic oils 5W30 and 5W40 mainly lies in their high-temperature viscosity. 5W30 has lower high-temperature viscosity, making it suitable for normal driving or mild climates. It is thinner at high temperatures, helping the engine run more smoothly and potentially improving fuel efficiency slightly. However, 5W40 has higher high-temperature viscosity, forming a thicker oil film in hot weather or under high-speed loads to protect the engine from wear. For example, when driving city roads in the north, 5W30 is both convenient and fuel-efficient; switching to 5W40 for long-distance mountain driving in summer helps avoid overheating issues. It also depends on the vehicle model—my old car, which has been running for over 30 years, saw reduced engine noise after switching to 40. In summary, the former focuses more on efficiency and daily use, while the latter offers enhanced protection. Choose based on the car's age and driving habits, and don’t ignore the vehicle manual recommendations.
I commute daily in the city and have used both 5W30 and 5W40. The difference is simple: 5W30 is relatively thinner, starts up faster, and offers better fuel efficiency for short trips and normal temperatures; 5W40 is more viscous, suitable for high-temperature environments or long-distance driving to prevent oil consumption. My car originally recommended 30-grade, but after moving to the south last year where it's hotter, I felt that 40-grade provides better protection, keeping the engine running smoothly. The key is to adjust based on region and usage—30-grade for easier cold starts in cooler climates, 40-grade for peace of mind in hot areas. Don’t switch brands randomly; always check the label and follow the manufacturer’s guidelines first.
