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Hydraulic Oil 101 : A Complete Guide to Hydraulic Oils

What is hydraulic oil?

Hydraulic oil is very different from other types of oils and lubricants. Hydraulic oil is a non-compressible fluid which is used to transfer power between hydraulic machinery and equipment. It is also commonly known as hydraulic fluid. It can be generally synthetic- or can also be mineral-based.Although the main role of this fluid is to transfer power, hydraulic fluid can also act as a coolant, sealant or as a lubricant within the machinery and equipment.

What is the main difference between synthetic and mineral based hydraulic oil?

Although there are various types of oil, lubricants and bases but the majority of these are mineral based or synthetic. So the mineral based hydraulic oils are produced from crude oil fractions but the synthetic hydraulic oils are made up of chemically produced base oils or fluids.

Synthetic oils are generally formulated to add superior physical properties as compared to basic mineral oils. It helps in high temperature performance; add biodegradability and also oxidation stability.

How Do Hydraulic Systems Work?

The main role of the hydraulic oil in the system is to transfer as much power as possible from the one end of that system to the other end through its hydraulic components. When there is an external force applied to the non-compressible hydraulic fluid which is usually driven from a piston within the cylinder – that oil is then pushed through the hydraulic chamber and thus ultimately generates a force on the other part of the system which is also called as target end. This results in a massive movement or action. This output is used to drive performance and achieve the end result.

While applying the force to the object produces compression. Best part of hydraulic oil is that they are non compressible which means that the liquid/fluid cannot be compressed at all. Mainly all the liquids are compressible to some degree but with hydraulic oil it is nil. Gases are also compressible that is why it can’t be used in hydraulic systems.

What Is Hydraulic Oil Used For? What Are Its Uses And Applications?

There are various ways to use hydraulic oils. It is used in a wide variety of applications across many industries. Just to give you some insight into the uses for hydraulic fluid and why it plays a crucial role in almost all types of industries and verticals are as follows:

• Lift Trucks

The hydraulic system within the trucks and stackers will help in lifting the heavy goods with ease because of the hydraulic systems built in the truck. Hydraulic oils make it possible.

• Automotive Lifts

One of the key applications of hydraulics is seen in car lifts (car jacks, automotive lifts, etc.). It requires hydraulic jack oil to make it possible because of the power generation.

• Wright Mowers

It is a mower that works well in cemeteries and other restrictive grassy regions. Again, the hydraulic part of the machines needs hydraulic oil for power.

• Snow Plows

Hydraulic oil is used for a snow plow equipment which is essential in the powerful operation wither it is lifting, tilting or moving the snow plow blade. Antifreeze properties of the hydraulics help it perform with ease which may not be possible with any other fluid.

• Skid Steer Loader

Skid steer hydraulic plays a big role at all times.

• Aircraft (Aviation)

In the aviation industry, it is the hydraulic oil which is reliable and useful in all circumstances. It is used in aviation control systems, hangar doors, jacks and controls for aircraft

• Tractors

There is a dedicated hydraulic oil for tractors since it operates under tough conditions.

• Cruise Ships

Hydraulic is used in cruise ships to carry out daily operations be it transporting goods or operating the heavy machineries including the engine of the ship.

• Marine Industry

Hydraulic oils play a significant role for marine industry as it relies heavily on heavy machinery and equipment but thanks to hydraulic oil they are able to do it with ease.

Hydraulic Fluid Properties

Now the question arises what are the key properties and characteristics of hydraulic oil which are crucial to perform the tasks for both commercial and industrial applications?

We can summarize them as follows:

  • Non-compressible
  • Thermally stable
  • Anti corrosion properties
  • Anti-wearing properties
  • Water resistant
  • Longevity
  • Cost Effective
  • Efficient

These are some of the most important properties of hydraulic oil. It is recommended to use only high quality oils for optimum results and to achieve greater performance. There are a wide range of hydraulic oils available in the market therefore you should choose carefully and from an authentic suppliers.

Hydraulic Oil Additives

There are extra additives which are required from time to time to help perform better under different conditions. Some of the common hydraulic fluid additives include:

  • Anti-wear

It does not only help prolong the life of equipment and the machinery but also improves the overall performance of the system.

  • Cold flow

Some additives are required to enable operations of the machinery and equipment under extreme cold weather conditions.

  • Anti-foaming

This is also required to control and limit the foaming of the oil. Anti foam additive make this possible and it is highly effective.

  • Anti-oxidant

It helps in preventing sludge formation.

  • Anti-rust

These additives form a protective coating which decreases the risk of rust damage in the system because of oxygen contact.

Hydraulic oil properties can be adjusted based on the type of additives which are used, but the most common types have a high viscosity index and are also incompressible. Thus, additives play a crucial role in controlling and adjusting the application of the hydraulic oil depending on the requirements and conditions. So hydraulic oil with the following applications can be achieved:

  • Hydraulic oil for low temperature conditions
  • Hydraulic oil for high-temperature applications
  • Hydraulic oil for heavy-duty use
  • Environmentally-friendly hydraulic oil

Hydraulic Oil Grades

There are various specifications available to choose from and they are typically determined most importantly by the weight and viscosity of the oil.
Further, main hydraulic oil is classified into the following two types.
They are L-HM and L-HV. What are HM and HV grades?

HM Hydraulic oil:

Hydraulic oil with anti-foaming, anti-corrosion, anti-rust and anti-wear performance.

HV Hydraulic oil:

Hydraulic oil with anti-foaming, anti-corrosion, anti-rust and anti-wear performance having high viscosity index used for hydraulic circuits subject to strong temperature variations as well as load constraints and very high pressures.

Hydraulic Oil Viscosity Explained

The viscosity of a hydraulic fluid is perhaps the most critical element when it comes to the transfer of hydraulic power. Again, it depends upon its applications. The ideal range for viscosity of a fluid is often between the range of 10 and 100 cSt.

Hydraulic Oil Viscosity Index

Key point here is that Viscosity index must not be confused with viscosity. Viscosity Index is a different parameter and is used differently to determine the applications. People often get confused between these terms and also end up using it interchangeably. Thus, it is important to get the basics right. It becomes extremely important to know the difference and have better clarity, let’s find the difference between these two important terms in the world of oils:

Viscosity – Viscosity or viscosity rating is a measure of oil’s resistance to flow. It is a crucial element of hydraulic oil. Since oil’s viscosity often changes with respect to temperature, it is reported based on temperature, for example @ 40°C. Lower viscosity fluids tend to flow more easily and quickly, whereas high viscosity fluids usually flow slowly because of its thickness.

Viscosity Index – Whereas viscosity index denotes the extent of thickness, or resistance to the flow, with relation to temperature.

The SAE (Society of Automotive Engineers) created a classification table (VI Scale) to show low to high viscosity levels depending on temperature °C. Originally the scale only went up to 100°C but with advances in hydraulic oil blends, the scale now goes above this number!

Viscosity IndexClassification
110°C and greaterVery High

The higher the number or the grade, the better the resistance to temperature change. This range is important for the classification of viscosity and to assess the quality of hydraulic oils.
It is only when you understand these terms will you be able to spot the right set of hydraulic oil or any type of engine or lubricant for your machine. With right knowledge and understanding you can make the right decisions.


There are various types of lubricants and hydraulic oils available in the market. Experts advise to carefully check the standards of the oil and lubricants before buying. It is advisable to buy it from authentic and trustworthy suppliers. At Shield oils, we believe in maintaining high standards of products. We know what our clients look for. Get in touch with us, if you are looking for the best quality hydraulic oils or lubricants. We are one of the best and most trusted supplies and manufacturers of lubricants.

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  1. Thanks for pointing out that there are different commercial lubricants I should consider depending on the usual temperature my machines would be having. I will be opening my own business soon and one of my first major goals for it would be to open its own factory for production once it gets big enough. As such, proper knowledge of heavy machinery and their maintenance would be very important to understand later down the line.

  2. Can you send me your website. So that we can go further.