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Hydraulic Oil Guide - Facts and Information

Read our detailed guide on commercial and industrial hydraulic oil including its uses, properties and differences. To purchase hydraulic oil, call 0330 678 0880 today.

Our Guide to Hydraulic Oil

It can be tricky knowing which hydraulic oil is best to use for your machinery when there is a range of factors involved. So, let us give you a detailed insight into hydraulic oil, where we cover topics such as its uses, production and viscosity.

Click on the below questions to take you right to the answer!

hydraulic oil

What is hydraulic oil?

Hydraulic oil, also known as hydraulic fluid, is a synthetic or mineral-based, non-compressible fluid that’s used to transfer power in hydraulic machinery and equipment. At Nationwide Fuels, we supply 99% mineral-based hydraulic oils.

No operation is feasible without hydraulic oil. Made up of oils and additives, it transfers power whilst also acting as a lubricant and coolant. It works in a large range of temperatures and reduces wear, corrosion and rust.

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

Most oils are either synthetic or mineral-based. Mineral based hydraulic oils are derived from crude oil fractions, whereas synthetic hydraulic oils are manufactured using chemically produced base fluids.

Synthetic products can be formulated to impart superior physical properties as compared to mineral oils, such as high temperature performance, oxidation stability and biodegradability.

What is hydraulic oil used for?

As well as to transfer power, it also serves as a lubricant, coolant and sealant in machinery and equipment. It is used in pretty much every industry due to their large number of benefits; application examples include:

  • Forklift trucks and stackers – to power the forks which lift heavy goods
  • Wood (log) splitters – to power the ram mechanism on a hydraulic oil log splitter
  • Agricultural machinery and vehicles – to operate the hydraulic brakes and hydraulic systems such as boom arms
  • Aircraft – hydraulic oil must be reliable for control systems, aircraft hangar doors, aircraft jacks and aircraft controls
  • Automotive lifts – car lifts and car jacks require hydraulic jack oil to provide safety as well as performance
  • Nautical – for marine vessel stabilisers to reduce the amount of oil which can affect a ship’s balance and cause sea sickness
  • Snow ploughs – an essential component in the operation of the hydraulic lift, tilt and angle movements, and blended with anti-freeze additives
  • Construction – used in a range of light, mid and heavy-duty construction machinery such as cranes, excavators and tipper trucks

Hydraulic oil additives

Depending on what you use hydraulic fluid for, there may be additional additives that are needed to help it perform well under different operating conditions. Additives include:

  • Anti-foaming – reduces foaming caused by detergents in the fluid, which can reduce the lubricating aspect of the fluid and cause machinery damage
  • Anti-oxidant – allows the oil to be used for longer and reduces sludge build-up
  • Anti-rust – forms a protective coating which reduces damage from rust and oxygen
  • Anti-wear – helps extend the lifetime of equipment (AW hydraulic fluids)

The above additives can be used on their own or in conjunction with other blends created for different functions. A hydraulic oil’s properties can be adjusted depending on which additives are used its general characteristics include a high viscosity index and being incompressible.

Common uses of hydraulic oil and the type of additive(s) used to help optimum performance


  High heat Heavy-duty Cold weather
Examples Hot metal shears

Coke furnace door openers

Diecasting machines

Construction machinery Offshore supply



Problem Under high heat, oil becomes less viscous and flows easier which can cause leaks, rapid deterioration or loss of the required properties High-pressure environments will break machinery In arctic conditions, oil can start to solidify – if equipment is not properly lubricated it will seize up
Solution Additives retain their viscosity when exposed to high temperatures Anti-wear additives to cope under pressure Anti-freeze additives to avoid freezing or waxing. Low-temperature hydraulic oil is a popular name for fluid used here.

Is there a difference between hydraulic oil and hydraulic fluid?

Although hydraulic oil and hydraulic fluid are terms that are often used interchangeably, there are some subtle differences.

Hydraulic fluid has the same uses as hydraulic oil, more commonly used in aircraft systems and automobile systems such as automatic transmissions, power brakes and steering.

Hydraulic oil ratings

Many end-users require ratings and approvals so they can rest assured that they’re using the correct oil for their equipment and machinery.

When a company sells an additive pack, they work with a manufacturer to produce an oil that works seamlessly with the manufacturer’s application. This will be traceable by a hydraulic oil supplier who has used the additive in the fluid.

Hydraulic oil grade list

  • AGMA – (American Gear Manufacturer’s Association, leading gear oil standards).
  • SAE – (Society of Automotive Engineers).
  • ISO VG – (International Standards Organisation). The higher the VG number the more viscous the fluid is. The VG number refers to which hydraulic oil is thicker, also known as the hydraulic oil weight.

Grades with a W next to them indicate the weight (apart from automobile engine oil, which refers to winter oil). In the UK, ISO VG is used mainly for grading hydraulic oil.

A rough guide to common hydraulic oil ISO grades and their applications

  • ISO 15 Hydraulic Oil – typically used in power steering and hydraulic brake systems
  • ISO 22 Hydraulic Oil – generally used in airlines for air tools etc.
  • ISO 32 Hydraulic Oil – ideal for use in high-powered machine tools
  • ISO 46 Hydraulic Oil – normally required for industrial plant working under high-pressure etc
  • ISO 68 Hydraulic Oil – designed for use in systems which require a large load-carrying ability
  • ISO 100 Hydraulic Oil – tends to be used in industrial machinery with heavy loads

Please note, some grades may cross over so it’s important to check with your supplier or manufacturer before use. Call us on 0330 678 0880 to find out which hydraulic oil is right for you.

Hydraulic oil properties

Its properties are what make it so popular in commercial/industrial applications and are key in a hydraulic system’s ability to work under harsh operating conditions. Good hydraulic oils have a combination of the following properties:

  • Non-compressible
  • Fire-resistant
  • Non-corrosive
  • Thermally stable in a range of temperatures
  • Anti-wearing
  • Unable to cavitate
  • Tolerant to water (resistant to water contamination)
  • Long-lasting
  • Cost-effective
  • Viscous, regardless of temperature

There are very few oils that perfectly adhere to the above criteria. However, there are a range of hydraulic oils that are specialised for the environments in which they are required to operate

Hydraulic oil classification

This refers to fluids that have different performance levels. Examples include:

  • HL: refined mineral oils with anti-rust and anti-oxidation properties
  • HM: the same properties as HL with improved anti-wear properties
  • HH: non-inhibited refined mineral oils
  • HR: HL oils with VI improvers

For more information, give us a call on 0330 678 0880 or visit here.

Hydraulic oil analysis

Also referred to as condition monitoring, it provides a detailed look at your oils to help you get the most out of them before switching your hydraulic application or damaging machinery.

At Nationwide Fuels, we offer hydraulic oil analysis to all industries. We take a sample, analyse it in our onsite laboratory and provide you with a detailed report on whether you’re using the best oil for your application or whether an alternative would be better suited. This provides complete peace of mind that your expensive equipment is in safe hands and protected against dirty or worn oil.

If you’re a regular user of hydraulic oil, analysis should be high on your list. The benefits include:

  • Cost-effective solution to avoid unnecessary replacement
  • Reduces damage to machinery by identifying any issues early on
  • Enhanced life and performance of machinery and oil
  • Reduces risk of operating injuries and costs in claims, damages and downtime

Hydraulic oil flashpoint

Hydraulic oil flash point refers to the lowest temperature at which enough vapours are released from the fluid which are combustible. This is typically between 260 – 399°C. The lower the flashpoint, the easier it is to ignite.

They play a crucial part in commercial applications so it’s important that you purchase them from a reputable fuel supplier like Nationwide Fuels. Get in touch today on 0330 678 0880 to find out more.

Hydraulic oil temperature range

Depending on what hydraulic oil is used for, it may endure both hot and cold temperatures which can render it useless if the oil hasn’t been blended with the right additives.

Hydraulic oils have temperature stability which simply means that they will maintain their properties within a particular temperature range. Anything outside of this range will have a negative impact on its temperature stability, causing the fluid to either wax or freeze in cold temperatures or lose viscosity and potentially leak in excessive heat.

Hydraulic oil viscosity

Viscosity is a key property of hydraulic oil and is the measurement of its resistance to flow. This means that it will resist compression at different rates depending on its viscosity and will take longer to pass through an orifice as the viscosity increases.

Hydraulic oil with a high viscosity will be thicker and harder to compress and move, whereas a low viscosity oil will be thinner and pass through much easier. The viscosity is measured in Centistokes (cSt) at temperatures of 40°C or 100°C in a laboratory setting using a viscometer. The value will always have the temperature next to it, as without this it’s meaningless.

The viscosity is key in many different applications – the wrong viscosity could make the equipment function poorly.

The viscosity and temperature of hydraulic oil are closely linked. As the temperature increases, the viscosity decreases – think of oil in a cooking pan; as the pan heats up, it becomes much more liquefied. Likewise, as the temperature decreases, the oil becomes more viscous.

Viscosity index

The viscosity index (VI) is used to measure a change in viscosity of hydraulic oil under changing temperatures. If it has a low viscosity index, a change in temperature will affect the viscosity more than if it has a high viscosity index.

Hydraulic oil with a high viscosity index is usually used in an application with a greater range of ambient/operating temperatures.

A straight paraffinic mineral base oil tends to produce an oil with a low viscosity index, whereas one with viscosity improvers will produce a fluid with a high viscosity index.

The Society of Automotive Engineers (SAE) created a classification table (VI Scale) to show low to high viscosity levels depending on the temperature (°C). In the early days, the scale only went up to 100°C, however advances in hydraulic oil blending mean that the scale now goes much beyond this number.

hydraulic oil viscosity

Viscosity conversion chart

hydraulic oil viscosity

To understand the above chart, you need to read horizontally. It assumes 96 VI single grade oils, which is equivalent to viscosity at 40°C only.

Viscosity limits are simply a guesstimate; for more accurate data you should refer to your hydraulic oil supplier, ISO, AGMA and SAE specifications.

W grades are represented in terms of approximated 40°C viscosity. For low-temperature limits, you must check with SAE specifications.

How do hydraulic systems work?

The primary role of hydraulic oil is to transfer power from one end of a system to another end using a variety of hydraulic components.

An external force, such as a piston within a cylinder, is applied to the hydraulic oil which pushes the oil through the hydraulic system. Eventually, this produces a force on another part of the system which then results in a movement or action.

Please note that a key property of hydraulic oil is that it’s non-compressible, allowing for the most efficient transfer of force.

What is hydraulic oil made of?

Hydraulic oil is made up of one base fluid and then a number of additional ingredients which can be mixed depending on the desired properties required by your operations.

Examples include:

  • Esters
  • Mineral oil
  • Glycol
  • Silicone
  • Ethers

Environmentally-friendly hydraulic oil

Biodegradable hydraulic oil is commonly used in applications where a spill or leak could contaminate the environment. The typical base oil in these fluids includes rapeseed oil and other vegetable oils which means that it will degrade naturally in the event of an accidental spill.

If you operate a farm, forest or environmentally sensitive site, environmentally-friendly hydraulic oil should be strongly considered for your operations.

Hydraulic oil price

As you can see, hydraulic fluids are an essential part of industrial and commercial applications. Pick the right hydraulic oil and the benefits add up; productivity gains and reduced overall operating costs. Nationwide Fuels deliver hydraulic oil in a range of quantities to businesses across the UK within 48 hours of purchase.

Wondering which hydraulic fluid to choose for your system? To learn more or request a price, call our oil experts today on 0330 678 0880.

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