Is hydraulic oil the same as engine oil? What is the difference between hydraulic oil and engine oil?

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Regarding this issue, first of all: hydraulic oil is not engine oil, and it is important to clearly distinguish between the two to avoid mixing them up during use. In China, hydraulic oil is primarily used in various hydraulic systems, and its viscosity grade is determined by the operating conditions of those systems. The additives used include antioxidants, rust inhibitors, and anti-wear agents, which are quite different from those found in diesel engine oils. Therefore, we must never use hydraulic oil as engine oil. In terms of application areas, hydraulic oil is primarily used in the industrial lubricant sector, whereas engine oil is more commonly used in the automotive industry; these are some of the differences in their areas of use. In terms of their external color, hydraulic oil is usually a golden-yellow transparent liquid, while engine oil tends to have a slightly bluer color. From a manufacturing perspective, most hydraulic oils are considered semi-finished products. Their notable feature is their ability to withstand high pressures, although their production process is slightly less sophisticated than that of engine oils. One of the most prominent characteristics of engine oil is its lubricating function. Compared to hydraulic oil, the particles in engine oil have smaller sizes, and its viscosity is generally higher than that of hydraulic oil. Regarding the question raised by many netizens about using hydraulic oil as engine oil, it is not recommended to mix these two types of oil together under normal circumstances; after all, their functions and effects differ, and this point must be kept in mind.