Can fully synthetic oils from different brands be mixed?
2 Answers
Fully synthetic oils from different brands should not be mixed. Although the base oils are similar, the processing techniques and additives vary between brands, and even different grades within the same brand may use different additives. Mixing them can lead to chemical reactions between the additives, causing the oil or hydraulic fluid to lose its original physical and chemical properties. This can result in the failure of lubrication, cooling, and pressure transmission functions, potentially leading to vehicle or mechanical failures or even severe damage. Fully synthetic oil is a product of modern chemical technology advancements, offering superior lubricity, lower friction resistance, resistance to oxidation, and strong cleaning properties compared to mineral oil.
I think it's best not to mix different brands of full synthetic engine oils, mainly because their formulations vary too much. The base oils of full synthetics are similar, but the additives each brand uses—like detergents, anti-wear agents—are completely different. Mixing them could trigger chemical reactions that form sediment or clumps, compromising lubrication. If oil passages get clogged or oil pressure drops, the engine risks overheating or accelerated wear. From cases I've studied, some owners had no immediate issues with temporary mixing, but long-term it hikes maintenance costs. In emergencies like running low mid-trip, a small amount of the same grade full synthetic can be mixed as a stopgap, but switch back to a single brand ASAP. Using matched oil during maintenance with regular changes saves money and protects your engine.
