The Difference Between Semi-Synthetic and Full Synthetic Engine Oil

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Full synthetic engine oil is more expensive than semi-synthetic engine oil. The differences between full synthetic and semi-synthetic engine oils are as follows: Difference 1: Different base oils. Semi-synthetic engine oil uses Group III base oil; full synthetic engine oil is a blend of Group III, IV, and V base oils. The replacement intervals differ—semi-synthetic engine oil should be replaced every six months or 7,500 kilometers, while full synthetic engine oil can last one year or 10,000 kilometers. Difference 2: Operating temperature range. Full synthetic oil has a wider temperature range. Under the same conditions, it can protect the engine with lower viscosity, whereas semi-synthetic oil has higher requirements. Applicability also varies—semi-synthetic oil is more suitable for economical small-displacement engines with smooth driving, while full synthetic oil performs well under harsh conditions, offering better high-temperature resistance and low-temperature performance. Difference 3: Different additives. Full synthetic oil contains higher TBN (Total Base Number) additives, extending oil life and improving engine cleanliness. Semi-synthetic oil has lower TBN content, shortening the maintenance interval and potentially producing sulfated ash. Due to premium base oils and superior additives, full synthetic oil exhibits less volatility, greater stability, reduced friction, and viscosity that remains stable across temperature changes. Difference 4: Price difference. Full synthetic oil involves more advanced refining and additive technologies, resulting in higher production costs. Thus, it is priced higher than semi-synthetic oil. Performance-wise, full synthetic oil outperforms semi-synthetic oil, providing better engine protection and internal cleaning.