Which is thicker, 5W30 or 5W-40?

5W-40 engine oil has a higher viscosity than 5W-30, which is mainly reflected in the oil film thickness and shear resistance in high-temperature environments. It is suitable for new cars or low-mileage vehicles (within 100,000 kilometres), as it can improve cold start speed and reduce fuel consumption by approximately 0.3-0.5 L per 100 kilometres. In contrast, 5W-40 has a high-temperature viscosity of 12.5-16.3 mm²/s, with a thicker oil film, providing stronger protection for high-load operating conditions (such as turbocharged engines, long-distance high-speed driving or aggressive driving) and old engines (it can reduce oil consumption by more than 50%). New Japanese, Korean and American cars usually recommend 5W-30, while German turbocharged cars or driving in high-temperature areas are more suitable for 5W-40. At the same time, it should be noted to avoid mixing oils of different viscosities and regularly check oil consumption for dynamic adjustment.