What is the difference between 5w30 and 5w-40?
2 Answers
The letter 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 differences between 5w30 and 5w40 engine oils are as follows: 1. Different kinematic viscosity standards at 100 degrees Celsius: 5w40 has higher viscosity than 5w30, while 5W-30 has slightly lower viscosity than 5W-40, providing better protection under high-temperature conditions. 2. Differences in fluidity and protection: The lower the oil viscosity, the thinner the oil film and the better the fluidity, but under high temperature and high pressure, the protection is worse.
I've been driving different car models and frequently switch between 5W30 and 5W40 oils. From experience, there's little difference between them during cold starts in winter—both allow the engine to rotate smoothly since the 5W indicates the same low-temperature fluidity. However, in summer heat, the difference is noticeable: 5W30 is thinner, with less resistance, saving about 5% on fuel. My car gets better fuel efficiency with this in mild climates. On the other hand, 5W40 is more viscous, forming a thicker oil film in hot weather to protect engine components and prevent wear, making it suitable for hot regions or long-distance driving. I've also found that choosing the wrong oil can affect performance—for example, using 5W30 in high-temperature areas may lead to increased engine noise. The key is to follow the vehicle manual, as some engines specify 30 or 40, which can impact warranty. Overall, 30 viscosity is ideal for daily fuel savings, while 40 offers stronger protection under thermal load conditions.
