Why can't automotive lubricants be mixed?

There are still many varieties of automotive lubricants on the market, and car owners can try products from many brands. However, especially with engine oil, there are significant differences between different types. The formulations of lubricants from different brands are certainly not the same. So why can't automotive lubricants be mixed? Below, the editor will briefly explain to everyone.

All types of automotive lubricating oils share the same base oil, differing only in viscosity grades, with the distinction lying in the variety and quantity of their additive components. Therefore, lubricating oils are typically classified by the type and amount of additives they contain. Lubricating oils with different additive formulations must not be mixed, as this could cause chemical reactions among the additives in the oil, impairing the intended performance of the lubricant or potentially leading to machine damage.

With the continuous improvement of additives and their formulations, some universal oils have been developed and produced. For example, lubricating oils such as QE/CC and QF/CD for gasoline and diesel engines can be used universally within the specified grade range. Therefore, whether lubricating oils can be mixed should be determined based on the requirements of the manual, comprehensively comparing the name, type, and brand of the oil, and reasonably selecting the appropriate grade and brand for use.

Even within the same type of engine oil products, there are different viscosity grades. I clearly remember a friend once saying: "I think 40 viscosity oil is a bit too thick, and 30 is a bit too thin, so I plan to mix them together—35 viscosity should be just right!" I just want to say: "Dear, I know you're good at math, but viscosity isn't calculated that way." This is similar to the issue with antifreeze's freezing point—mixing high and low freezing point antifreeze doesn't result in an average freezing point.