Castrol's best all-synthetic engine oil is Castrol Polar Protection, which belongs to all synthetic engine oil with Class III base oil, and its maintenance mileage is about 10000 km. At present, synthetic engine oil is about 10,000 kilometers, and there is not much difference. However, I use GT Maroon 5 engine oil with four types of PAO, which is of higher quality and can maintain 15000 km, which is more durable than the general three types in synthetic engine oil.