Should I use 5W30 or 5W40 in summer?

Under Malaysia's year-round high-temperature climate, high-temperature protection performance should be a key consideration when choosing engine oil. The main difference between 5W30 and 5W40 lies in their high-temperature viscosity. The former has a kinematic viscosity of 9.3-12.5 mm²/s at 100°C, featuring a thinner oil film and better fluidity, making it suitable for new vehicles or precision engines (such as Japanese models). It can reduce fuel consumption by approximately 3%-5% and ensures quicker cold starts. The latter has a viscosity of 12.5-16.3 mm²/s, offering a thicker oil film and 20% greater shear resistance, making it particularly suitable for older vehicles (with over 80,000 kilometres), turbocharged models, or frequent long-distance high-speed driving in high-temperature environments (exceeding 30°C). If the vehicle manual does not specify requirements, German cars or high-mileage vehicles should prioritize 5W40 to enhance high-temperature sealing, while newly purchased Japanese or Korean vehicles may benefit more from 5W30 for improved fuel efficiency. Although March is currently a transitional season, given the anticipated temperature rise, switching to 5W40 in advance would be a more prudent choice if the vehicle exhibits minor oil consumption or frequently operates under high-load conditions.