Hydraulic Oil vs Lubricating Oil: The Differences Explained

What is lubricating oil and what is hydraulic oils?

Lubricating oil

Lubricating oil

Lubricating oil is a kind of lubricant.

It is between two relatively moving objects and has the function of reducing the friction of two objects due to contact.

In addition, it has the functions of cooling, rust prevention, cleaning, sealing and buffering.

Lubricating oil is divided into diesel engine oil and gasoline engine oil.

They each have different grades to choose from.

Hydraulic oil

Hydraulic oil

Hydraulic oil is a hydraulic medium used in hydraulic systems that use liquid pressure energy.

It plays the role of energy transmission, anti-wear, system lubrication, anti-corrosion, anti-rust, cooling and sealing in the hydraulic system.

Hydraulic oil is a special oil that transmits pressure ( power ).

It is divided into common hydraulic oil, anti-wear hydraulic oil and low-condensation point hydraulic oil.

Engineering machinery hydraulic oil is a hydraulic system special oil developed for the actual working environment requirements of construction machinery and die casting machine.

Compared with other hydraulic oils, engineering machinery hydraulic oils have better wear resistance, rust resistance, emulsification resistance, oxidation stability, hydrolysis stability and thermal stability.

Similarities and differences between lubricating oil and hydraulic oil


From the above explanation, we can see that lubricating oil and hydraulic oil also have the functions of anti-wear, cooling, rust prevention, cleaning and sealing.

And this is why we often hear some words about the use of hydraulic oil as a lubricant.


  1. The main role is different.

In the main role, lubricating oil and engineering machinery hydraulic oil are still different.

The main function of the lubricating oil is to reduce the damage caused by the friction of the object; the main function of the hydraulic oil of the engineering machinery is to transmit the pressure (power).

  1. The focus is different.

Because of their different main functions, lubricants are more focused on reducing friction, reducing wear and preventing metal sintering.

The hydraulic oil pays more attention to the viscosity index, which requires the hydraulic oil to perform well at high temperatures to ensure easy flow at low temperatures and reduce energy consumption.

Hydraulic oil and lubricating oil selection

Lubricating oil selection

It is very important to select the appropriate oil type and level of use based on the operating conditions of the engine.

I believe many of you know that the choice of lubricants should be based on the seasonal temperature of the region to select the appropriate lubricant label and viscosity grade.

Hydraulic oil selection

The rational selection of hydraulic oil is the first step in the correct use of hydraulic oil.

In general, the selection of hydraulic oil should follow the following principles:

  • Excellent performance
  • Economically reasonable
  • Reliable quality
  • Easy to manage
  1. When using hydraulic oil, we need to select hydraulic oils with low volume expansion coefficient and high specific heat capacity.
  2. The hydraulic oil has a low flow point and freezing point. The high ignition point and flash point must also be considered when selecting hydraulic oil.
  3. When choosing the viscosity grade of hydraulic oil, we mainly consider the working pressure, ambient temperature and speed of the hydraulic system. This is also different from the lubricating oil.

After selecting suitable hydraulic oil, it is very important to manage and maintain during use. Pay attention to the following points:

① Prevent hydraulic oil from being contaminated

The biggest hazard of pollutants is corrosion of the equipment, clogging of filters and orifices, acceleration of oil aging and corrosion of components;

② Prevent air from entering

Mixing in air can cause cavitation and noise, and cause the hydraulic oil to deteriorate prematurely, affecting the use;

③ Prevent moisture from entering

The mixing of cooling water and steam will corrode the metal in the hydraulic system, accelerate the deterioration of the oil, and reduce the lubricity of the hydraulic oil;

④ Control the operating temperature of the hydraulic oil

For mineral oil type hydraulic oil, it can work continuously at 50~65℃, and the maximum service temperature is 120~140℃.

When the oil temperature rises, the oxidative deterioration of the hydraulic oil is accelerated, and the acid generated by the oxidation causes corrosion of the metal component.

What is the hazard of using hydraulic oil as a lubricant?

The viscosity of hydraulic oil is generally relatively small, and the viscosity of lubricating oil is generally relatively large.

Therefore, when hydraulic oil is used as lubricating oil, the formation of oil film is more difficult.

This is easy to cause the machine to wear more and even lead to more serious consequences.

The main role of hydraulic oil and lubricant is different.

Therefore, the additives in them are also different.

When the two oils are mixed, the performance changes and even the chemical reaction occurs, which causes the oil to deteriorate, which in turn causes the machine to wear more.

The operating temperature of the hydraulic system is not high, but the unit pressure of hydraulic oil transmission is very large.

However, the operating temperature of the engine crankcase is very high, coupled with the intrusion of high temperature and high-pressure gas in the combustion chamber, which will make the functions of the hydraulic oil fail more quickly, resulting in increased wear of the machine, which will lead to greater losses.

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1 thought on “Hydraulic Oil vs Lubricating Oil: The Differences Explained”

  1. Your answer to “What is the hazard of using hydraulic oil as a lubricant?” focuses on differences in viscosity.

    But could an ISO 68 hydraulic oil be used in a gear box as well as an ISO 68 circulating oil?

    Thanks for an informative article.

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