What is the difference between 5w30 and 5w40?

[StPeter]

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.

[LeGianna]

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.

[VanSadie]

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.

[LeElias]

When I ran an auto repair shop, I encountered cases where car owners misused engine oil. The most noticeable difference between 5w30 and 5w40 lies in their high-temperature performance. The 30 viscosity is thinner, offering better fuel economy, while the 40 is thicker, providing stronger high-temperature protection. In southern cities during summer, when stuck in traffic for half an hour, 40 oil remains more stable in the engine. A pickup truck that frequently carried loads showed reduced valve noise after switching to 40. However, using 30 is perfectly fine for new cars; only older or modified vehicles need to consider 40. Choosing the wrong oil might trigger the oil warning light, which is no small matter.

[StGia]

Last week my cousin asked me about the difference between these two engine oils. Simply put, it's about the viscosity variation under high temperatures. The 5w30 is suitable for most new cars, providing a lighter and more fuel-efficient drive. If you frequently race or drive on mountain roads, using 5w40 offers better engine protection. After switching to 40 in my old Jeep, the power output became much smoother when climbing hills. However, it's important not to mix them, as blending different viscosities can affect performance. For newer car models, 30 is sufficient unless you often drive fully loaded uphill.

[MacEmma]

My friend always struggles with seasonal maintenance. The key is to look at the numbers 30 and 40, which represent the high-temperature viscosity grade. A 30 has better fluidity, saving about half a liter of fuel in city driving. A 40 performs more stably when the engine overheats, making it especially suitable for older cars or turbocharged vehicles. When I was driving for Didi, I tested it—using 40-grade oil kept the RPM more stable during traffic jams with the AC on. However, you should adjust the maintenance cycle accordingly; high-viscosity oil recommends shorter oil change intervals. For new cars, 30 is perfectly sufficient, while older cars should consider 40 for better reliability.