Can Semi-Synthetic and Full Synthetic Engine Oils Be Mixed?
2 Answers
Semi-synthetic and full synthetic engine oils should not be mixed. The reason is that full synthetic oil contains no mineral oil, while semi-synthetic oil contains a small amount of mineral oil. Engine oil, also known as motor lubricant, is composed of base oil and additives. The base oil is the main component of lubricating oil, determining its basic properties, while additives compensate for and improve the deficiencies in the performance of the base oil. The differences between synthetic and semi-synthetic oils include: 1. Different base oils: Synthetic oil is a mixture of Group III, IV, and V base oils, while semi-synthetic oil uses Group III base oil. 2. Different replacement intervals: Synthetic oil has a service life of one year or 10,000 kilometers, whereas semi-synthetic oil should be replaced every six months or 7,500 kilometers.
As a long-time car enthusiast, I think mixing semi-synthetic and full synthetic oils is something to be really careful about. Full synthetic base oils are purer and have more stable molecular structures, and the additives in them might chemically react with those in semi-synthetics. Mixing them can alter viscosity and reduce lubrication effectiveness. I've seen fellow car owners experience increased engine noise or unexplained higher fuel consumption after mixing oils. Over time, this accelerates component wear, and replacing an engine is a huge hassle. It's best to stick to one brand of oil and avoid switching randomly. When changing oil, make sure to fully drain the old oil residue to prevent mixing issues. Always refer to the manual for oil recommendations—don't cut corners to save money, as safe driving comes first. In emergencies, a small mix might work temporarily, but get a full oil change as soon as possible afterward.
