Which has lower fuel consumption, 5w30 or 5w40?

[LeValeria]

Compared to 5w40 engine oil, 5w30 has lower fuel consumption, but this may vary depending on the specific vehicle model and usage environment. Here are the differences between 5w30 and 5w40: 1. Different high-temperature viscosity: 5W30 has smaller high-temperature viscosity, better fluidity, which helps reduce fuel consumption and allows faster engine cooling; 5W40 has higher high-temperature viscosity, is thicker, has poorer fluidity and greater resistance, but exhibits less fluctuation and is more stable. 2. Different applicable ambient temperatures: 5W30 can be used in summer environments with temperatures below 30 degrees Celsius, while 5W40 can be used in summer environments with temperatures below 40 degrees Celsius.