What is the difference between fully synthetic engine oil 5w30 and 5w40?

[VanAaliyah]

The difference between fully synthetic engine oil 5w30 and 5w40 lies in their viscosity: fully synthetic engine oil 5w30 has a viscosity of 30, while fully synthetic engine oil 5w40 has a viscosity of 40. In simple terms, 5w40 oil has higher viscosity than 5w30, providing better protection under high-temperature conditions. On the other hand, 5w30 flows better than 5w40, helping to reduce fuel consumption. The choice of engine oil should be based on the specifications in the car manual, as not all manufacturers' engines are designed the same. American engines, for example, are relatively more precise (with smaller gaps), making 5w30 oil (lower viscosity) more suitable. German cars typically have turbocharged engines with larger gaps, requiring the use of 5w40 oil (higher viscosity). Japanese and Korean cars often use oils with viscosities of 20 or 30, while European cars use oils with a viscosity of 40.