Is 5W-30 or 5W40 better for high mileage?

For high-mileage vehicles (over 100,000 km), 5W-40 engine oil is a better choice. Its high-temperature viscosity (12.5-16.3 mm²/s) effectively fills engine component wear gaps, reduces oil consumption (proven to decrease by over 50%), and enhances high-temperature sealing performance and oil film strength. While 5W-30 offers faster cold starts and better fuel efficiency (saving 0.3-0.5 L per 100 km), its thinner oil film (9.3-12.5 mm²/s) may inadequately seal worn components in older engines, increasing the risk of oil consumption. If the vehicle manual does not explicitly prohibit it, high-mileage vehicles should prioritize upgrading to 5W-40. However, low-temperature fluidity must still be considered during winter in northern cold regions. Regular dipstick checks are recommended to monitor oil consumption, and mixing different viscosity oils should be avoided.