What's the Difference Between Full Synthetic and Semi-Synthetic Engine Oil?
2 Answers
Here are the differences between full synthetic and semi-synthetic engine oil: 1. Different base oils: Full synthetic oil is blended from Group III, IV, and V base oils; semi-synthetic oil uses Group III base oil. 2. Different replacement intervals: Full 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. 3. Different vehicle suitability: Full synthetic oil is more commonly used in turbocharged engines and high-end luxury vehicles; semi-synthetic oil is more suitable for economical, small-displacement vehicles that prioritize smooth driving.
I've been driving for over 20 years and regularly maintain my engine. Simply put, full synthetic oil is man-made with highly purified base oil and strong heat resistance. It protects the engine from failing in summer or during high-speed driving, and has better longevity—needing replacement only every 7,500 to 10,000 km. It’s suitable for high-performance cars or harsh road conditions. Semi-synthetic oil is a blend of mineral and synthetic oil, offering good cost-performance but thinning more easily under high temperatures, providing slightly weaker protection. It requires inspection every 5,000 km. When I was younger, I used semi-synthetic to save money, but now I’ve switched to full synthetic—the engine runs smoother, starts faster, and is quieter. In the long run, it’s actually more cost-effective. Always check the manual’s recommendations, though. Never use lower-quality oil in a new engine to avoid premature wear.
