Hydraulic Oil vs Lubricating Oil: The Differences Explained

Difference Between Hydraulic Oil and Lubricating Oil

What Is Lubricating Oil?

Lubricating oil is a type of lubricant used to reduce friction between two moving objects that are in contact. It also serves several other purposes, including cooling, rust prevention, cleaning, sealing, and buffering.

Lubricating oil can be further divided into diesel engine oil and gasoline engine oil, each with various grades to choose from.

lubricating oil

What Is Hydraulic Oil?

Hydraulic oil

Hydraulic oil is a special type of lubricant used in hydraulic systems that operate through liquid pressure energy. Its role is multi-faceted, serving as a medium for energy transmission, anti-wear protection, lubrication, anti-corrosion and anti-rust, cooling and sealing.

This oil is specifically designed to transmit pressure and is divided into three types: common hydraulic oil, anti-wear hydraulic oil, and low-condensation point hydraulic oil.

Engineering machinery hydraulic oil is a specialized version of hydraulic oil, formulated specifically to meet the demanding requirements of construction machinery and die casting machines. This type of hydraulic oil offers improved wear resistance, rust resistance, emulsification resistance, oxidation stability, hydrolysis stability, and thermal stability compared to other hydraulic oils.

Differences Between Lubricating Oil and Hydraulic Oil


From the explanation above, it is evident that both lubricating oil and hydraulic oil possess similar functions such as anti-wear, cooling, rust prevention, cleaning, and sealing. This is why we often hear about the use of hydraulic oil as a lubricant.


  1. The main role is different.

In the primary role, lubricating oil and hydraulic oil for engineering machinery differ. The primary function of lubricating oil is to reduce the damage caused by friction between objects, while the primary function of hydraulic oil in engineering machinery is to transmit pressure (power).

  1. The focus is different.

Due to their contrasting main functions, lubricants primarily focus on reducing friction, reducing wear, and avoiding metal bonding. On the other hand, hydraulic oil places more emphasis on the viscosity index, requiring it to perform efficiently at high temperatures and to ensure smooth flow at low temperatures while reducing energy usage.

Hydraulic Oil and Lubricating Oil Selection

Lubricating oil selection

It is crucial to choose the right type and grade of oil based on the operating conditions of the engine. Many of you are aware that the selection of lubricants should be based on the seasonal temperature of the region to determine the appropriate lubricant label and viscosity grade.

Hydraulic oil selection

The proper selection of hydraulic oil is the first step in using it correctly.

Generally, the following principles should be followed when selecting hydraulic oil:

  • Excellent performance
  • Economically reasonable
  • Reliable quality
  • Easy to manage

When selecting hydraulic oil, it is important to choose one with a low volume expansion coefficient and a high specific heat capacity. Additionally, the hydraulic oil should have a low pour point and low freezing point. The high ignition point and flash point should also be taken into account.

When determining the appropriate viscosity grade for hydraulic oil, the primary factors to consider are the operating pressure, ambient temperature, and speed of the hydraulic system. This is distinct from the considerations for lubricating oil.

After choosing an appropriate hydraulic oil, it is crucial to properly maintain it during use. Consider the following points:

① Prevent contamination of the hydraulic oil

Contaminants can pose a significant hazard, including corrosion of equipment, clogging of filters and orifices, acceleration of oil aging, and corrosion of components.

② Avoid the introduction of air

Mixing air into the hydraulic oil can cause cavitation, noise, and accelerated deterioration of the oil, negatively impacting its performance.

③ Prevent moisture from entering the system

Mixing cooling water and steam with hydraulic oil can corrode metal components, accelerate oil degradation, and reduce the oil’s lubricity.

④ Control the operating temperature of the hydraulic oil

Mineral oil-based hydraulic oil can operate continuously at a temperature range of 50-65℃, with a maximum service temperature of 120-140℃. When the oil temperature increases, the oxidative deterioration of the oil is accelerated and the resulting acid can cause corrosion of metal components.

What Is the Hazard of Using Hydraulic Oil as a Lubricant?

The viscosity of hydraulic oil is typically lower while that of lubricating oil is generally higher.

As a result, when using hydraulic oil as a lubricant, it becomes more difficult for it to form an oil film, leading to increased wear on the machine and potentially even more serious consequences.

The primary role of hydraulic oil and lubricant differs, and their additives are also different. When the two oils are mixed, performance changes and chemical reactions may occur, causing the oil to deteriorate and leading to increased machine wear.

The operating temperature of a hydraulic system is not high, but the unit pressure of hydraulic oil transmission is significant. In contrast, the operating temperature of an engine crankcase is high and high-temperature, high-pressure gas from combustion can quickly cause hydraulic oil to fail, resulting in increased machine wear and greater losses.

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Founder of MachineMFG

As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.

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