What Are Different Types Of Hydraulic Fluid?

By Power Tools

March 10, 2021

There is a range of different types when it comes to hydraulic fluids and each one has its own unique properties.

Different machinery such as car transmissions and factory machinery used hydraulic fluid to run sufficiently.

Every type of hydraulic fluid is made with different chemicals with varying characteristics. Certain hydraulic fluids have a scent while others are completely odorless.

One fluid may be environmentally friendly when the next could be dangerous to our ecosystem.

What Are Different Types of Hydraulic Fluid

Determining which type of hydraulic fluid suits you best is generally down to a personal preference but there are a few important factors to consider first.

If your vehicle or machinery is in need of some care, hydraulic fluid could be the savior. Ensuring you find one that is compatible with seals, bearings, and other components is vital to help hydraulics run smoothly.

You should also consider its viscosity, fix resistance, and whether it is environmentally stable.

Using hydraulic fluid that is damaging to the environment could have dire consequences for many years to come.

To meet the various needs of different systems, there are six types of hydraulic fluids:

  • Petroleum-based fluids – Most commonly used. Readily available and economical with the best lubrication ability. Few corrosive problems. Compatible with all seal materials.
  • Emulsions (oil-in-water & water-in-oil) – Fluids mixed together that don’t chemically react with each other. Emulsions from petroleum-based oil are most often used. Oil-in-water has water characteristics but poor viscosity leading to leakage problems. Water-in-oil is fire-resistant with good viscosity and lubrication properties.
  • Water glycol – Nonflammable and commonly used for aircraft hydraulic systems. Low lubrication ability and not suitable for high-temperature applications. Prone to oxidation inhibitors. Toxic and corrosive toward zinc, magnesium, and aluminum. 
  • Synthetic fluids – Fire-resistant and suitable for high-temperature applications. Good viscosity and lubrication characteristics. Unsuitable for low-temperature applications. Not compatible with most sealing materials like nitrile.  Not environmentally-friendly.
  • Vegetable oils – Environmentally safe with good lubrication properties, average viscosity, and less expensive. Fire-resistant with certain additives. Easily oxidized and absorbs moisture. Requires good inhibitors to minimize any oxidation problems.
  • Biodegradable hydraulic fluids – Eco-friendly. Uses sunflower, soybean, rapeseed, etc as the base oil. Reduces pollution in cases of oil leaks or hydraulic hose failures. Similar to mineral oil-based anti-wear hydraulic fluids.

What is the difference between 32 and 46 hydraulic oil?

There are three grades to consider with hydraulic fluid; the viscosity grade and hydraulic oil type grade 32-46-68. The specifications are usually determined by the weight and viscosity of the oil.

The lower the number, the thinner the oil will be while the higher the number, the thicker the oil. Depending on temperatures, oil viscosity changes as it can become thinner in hotter temperatures and thicker in colder environments.

The main difference between 32 and 46 hydraulic oil is that 46 is thicker and has a more solid-like texture than 32-grade oil. Of course, 68 hydraulic oil is even thicker and more solid-like than 46.

What is the difference between ISO 46 and AW 46 hydraulic oil?

ISO (International Organization of Standardization) refers to the oil’s viscosity while AW stands for “anti-wear”. Each type of hydraulic equipment requires a different hydraulic oil.

AW oil is a premium oil designed for use with all hydraulic systems which recommend the use of anti-wear hydraulic oil. 

Most hydraulic oils are measured with the ISO grade but some with anti-wear properties are measured in other ways because they contain additives within the oil.

ISO 46 is not better or worse than AW 46 hydraulic oil. These numbers simply refer to the viscosity and not the quality of the oil. The quality is typically determined by the manufacturer.

What is the difference between ISO 32 and AW 32 hydraulic oil?

ISO 32 is the viscosity range for industrial oils. These are usually used in hydraulics but tell you nothing about the additives that may have been used.

AW 32 must contain anti-wear agents as well as other additives but these can be harmful to some applications.

The only difference is that there are additives contained within the oil when dealing with AW 32.

Can you mix different types of hydraulic fluid?

The short answer to this is, no. It is always best to avoid mixing different types of hydraulic fluids as each one has different formulations and additives contained within. These are added for different systems so it is not safe or reliable to believe two different hydraulic oils could be compatible.

Mixing different hydraulic fluids can cause serious damage to machinery and even be life-threatening. It is possible that an additive contained in one hydraulic fluid could travel up through certain hoses in vehicles and react with high hydraulic power and high voltage, potentially causing some sort of explosion.

Mixing fluids with different viscosities, but are still the same type, will impact the viscosity of the lubricant. The final viscosity will end up being variable and based upon the viscosities of the mixed fluids and how much fluid was mixed.

If the final viscosity is too low, the film thickness wouldn’t be enough to provide enough separation between two bearing elements and this could lead to failure. On the other hand, if the viscosity is too high, heat can generate and energy consumption can increase leading to a breakdown in the hydraulics.

Which hydraulic oil is thicker? 32 or 46?

Oil with a higher viscosity grade has thicker oil which is more solid-like. Therefore, 46 hydraulic oil is considerably thicker than 32. This is usually because hydraulic oil 46 weighs more as well.

Of course, hydraulic oil with a viscosity of 68 is much thicker than 46.

Is hydraulic oil the same as hydraulic fluid?

The main difference between hydraulic oil and hydraulic fluid is that the latter is used in automatic transmissions such as automobile systems. Hydraulic oil can not be used in these systems or for these purposes.

Out of all hydraulic fluids, hydraulic oil is the most common and this is why many people use these terms together. 

Hydraulic fluid is very useful in hydraulic systems such as excavators, garbage trucks, and hydraulic brakes. Hydraulic fluid is primarily used to transfer energy but it can be used in other ways too.

These range from heat transfers, sealants, lubrication, to the removal of contamination. These fluids typically have thermal stability, hydrolytic stability, a long life, have low chemical corrosiveness, and are a lower cost.

Hydraulic oil is a highly flammable fluid. It is helpful in energy transfer within a hydraulic system. As it is highly flammable, this oil shouldn’t be used in an igneous source.

If this occurs the oil spray can easily ignite under high-pressure conditions. This is one reason why many people prefer to use hydraulic fluid instead.

Hydraulic oil contains additives as well as oil. The oil isn’t only a medium for energy transfer but also acts as a coolant and lubricant. This helps to reduce corrosion in hydraulic systems allowing them to perform well under many different temperatures.

What is the difference between ISO and AW hydraulic oil?

Firstly, to understand what these hydraulic oils are, you will need to know what they stand for. ISO stands for International Organization of Standardization.

These are oils that meet the specifications of the ISO which have standards that require them to be met in most existing oils, food oils, cosmetics, medical oils, and industrial oils.

These standards were created over the years by various experts in each field. This was so oils could be of a certain quality and become easier to label. The ISO provides standards for the viscosity of hydraulic oils in order for the public to know exactly what they are purchasing.

AW stands for anti-wear hydraulic oil. ISO classifies these oils as HO (hydraulic oil). AW oils protect hydraulic machinery so that they last a long time and run efficiently. These oils are available in many viscosities and have a range of additives applied for anti-wear purposes.

AW oils are made from petroleum-based and an anti-wear additive (usually zinc dialkyl dithiophosphate – ZDDP) to protect the hydraulic pump. Each oil is made for specific application requirements so each one has unique purposes.

The base oil quality and quantity of additives mean that certain AW oils perform differently and affect the price point of various lubricants.

The main difference between both is that AW oils have additives contained in the oil while ISO oils do not.

Is universal tractor fluid the same as hydraulic fluid?

The most important factors of hydraulic oil are viscosity, wear corrosion and fire-resistant properties. These all affect the performance of a hydraulic system.

It can be considered that tractor fluid is a subcategory of hydraulic fluid as tractor fluids should be able to achieve most of the functions of hydraulic fluid.

Both fluids differ because of their properties and applications. While hydraulic oil is used to transfer power, tractor fluid is a medium for lubricating moving parts within the transmission such as bearings, final drives, and a wet brake system.

Although varied in their uses and purposes, tractor fluid and hydraulic fluid are similar but not the same.