What is the difference between 5w30 and 5w40?
3 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°C: 5w40 has higher viscosity than 5w30, while 5W-30 has slightly lower viscosity than 5W-40, offering better protective performance under high-temperature conditions. 2. Differences in fluidity and protection: Lower engine oil viscosity means thinner oil film and better fluidity, but provides poorer protection under high temperature and high pressure.
When I first bought my car, I didn’t understand the difference between 5W30 and 5W40 either. Later, the mechanic at my regular repair shop told me it mainly depends on driving habits. In winter, where temperatures drop below -20°C in our northern region, 5W30 allows for quicker cold starts and better fluidity during startup. During summer, when stuck in traffic or driving long distances on highways, 5W40’s higher viscosity provides better protection when engine temperatures soar. Since I drive an SUV and often take mountain roads in the suburbs, I’ve switched to 5W40 and noticed the engine noise has reduced significantly. However, if you mostly drive in the city for tasks like picking up kids, 5W30 is more fuel-efficient and cost-effective—it really depends on how you usually drive.
Yesterday, while helping my young neighbor pick out engine oil, we discussed this. The number before the W is 5, indicating similar cold-start performance. The difference lies in the numbers 30 and 40, where 40-grade oil has higher viscosity at high temperatures. Older German cars with higher engine temperatures and frequent long-distance driving are better off with 40-grade oil for peace of mind. Newer Japanese cars often recommend 30-grade oil for better fuel efficiency and environmental friendliness. After switching to 40-grade oil, my neighbor's decade-old Passat saw a noticeable improvement in its oil consumption issue. However, always check your maintenance manual—using the wrong grade might cause abnormal oil pressure.
