What is the difference between fully synthetic and semi-synthetic engine oil?
2 Answers
The differences between fully synthetic and semi-synthetic engine oil are: 1. Different replacement cycles: Fully synthetic oil should be replaced once a year or every 10,000 kilometers during use; semi-synthetic oil should be replaced every six months or every 7,500 kilometers during use. 2. Different applicable vehicle conditions: Fully synthetic oil can be used under various harsh conditions or when pursuing engine maintenance; semi-synthetic oil is more suitable for economical small-displacement vehicles with smooth driving. 3. Different additives used: Fully synthetic oil uses additives with high TBN content, making the oil last longer and clean the engine; semi-synthetic oil uses additives with low TBN content, shortening the oil maintenance cycle and producing sulfide ash.
I often do car maintenance myself, and there's quite a difference between full synthetic and semi-synthetic oils. Full synthetic is made from purely artificially synthesized base oils, with more uniform molecular structure, providing smoother cold starts in winter and better resistance to oxidation at high temperatures, allowing oil changes up to 12,000 km. Semi-synthetic is a blend of mineral and synthetic oils, offering a compromise in performance with a shorter oil change interval of around 8,000 km. Full synthetic is significantly more expensive, but if your car has a high-power turbocharged engine or you frequently drive long distances, it's worth the investment. I've seen engines opened up for inspection—those using full synthetic look as clean as new inside, while semi-synthetic ones show some sludge. The choice depends on your budget and usage conditions, but for peace of mind, full synthetic is the reliable option.
