Hydraulic oil

Introduction

Hydraulic oil, also known as hydraulic fluid, is essential for numerous industrial, agricultural, and mobile machines. Hydraulic oil is often underestimated, which is why OlieOnline is happy to draw more attention to these products. We will address: the differences between various types of hydraulic oil, what to consider when purchasing, the risks of using the wrong oil, and how to know when it needs replacement.
In this article, you'll get a complete overview with answers to all relevant questions, supplemented with recent real-world examples, facts, figures, and current insights from the hydraulics sector. Frequently asked questions are also extensively covered, such as: the difference between hydraulic oil and hydraulic fluid, which oil to choose for an excavator, oil change intervals, key properties of high-quality oil, mixing, purchasing, consequences of using incorrect oil, and how to know when it’s time for an oil change.

What is hydraulic oil and how does it work?

Hydraulic oil is a fluid specifically developed to transmit power within hydraulic systems. By moving this oil through the system, force is applied to components such as pistons, cylinders, or motors to transfer power.

• Power transmission: The primary function of hydraulic oil is to transmit power throughout the system.
• Lubrication: The oil reduces friction between moving parts, minimizing wear.
• Cooling: By absorbing and dissipating heat, the oil prevents overheating of components.
• Corrosion protection: Additives in the oil help protect metal components against rust and other forms of corrosion.
• Contamination control: High-quality hydraulic oil can effectively trap dirt and impurities, improving system performance.

In addition to acting as a power transmission medium, hydraulic oil also provides protection: it prevents metal-to-metal contact, offers lubrication, guards against wear, rust, and corrosion, and dissipates heat. These requirements are often overlooked when selecting hydraulic oil.

Hydraulic applications are common across agriculture, construction, industry, inland shipping, and transport sectors. Therefore, hydraulic oils are of critical importance. To give you an idea of the forces involved: industrial presses can operate at pressures of 700 bar or more. The higher the pressure, the higher the temperature generated in (servo) valves, and the more crucial fine filtration becomes! Tractors and aircraft often have other specific hydraulic oil r

What is the difference between hydraulic oil and hydraulic fluid?

In the Netherlands, the terms ‘hydrauliek olie’, ‘hydrauliekolie’ and ‘hydraulische olie’ are used interchangeably. Linguistically, ‘hydraulische olie’ is sometimes considered the correct term, but in commerce, industry, and technical documentation, all three mean exactly the same. Internationally, the term "hydraulic oil" or "hydraulic fluid" is used. When purchasing, you don’t need to worry about the naming; the specifications and standards (such as ISO VG 46 or DIN 51524 HLP) determine the right choice — not the name. Keep in mind that the quality of a hydraulic oil lies in how long it retains its performance.

Types of hydraulic oil: mineral, synthetic and biodegradable

Every hydraulic oil consists of a base oil combined with additives that are designed to improve specific properties:

• Base oil: Can be mineral or synthetic, depending on the application.
• Additives: These reduce oxidation, limit wear, stabilize viscosity, and promote water separation.

Generally, hydraulic fluids are divided into three main types:

1. Mineral: Made from refined petroleum with added anti-wear agents, antioxidants, and rust inhibitors. Most widely used globally (~85%).
2. Synthetic: Based on synthetic oil with PAO (polyalphaolefins) — synthetic hydrocarbons used in high-performance lubricants. They are Group IV synthetic oils (API classification) and are made by polymerizing alpha-olefins. Advantages include better performance under extreme temperatures and loads.
3. Biodegradable: e.g. Shell Panolin products, specially developed for use in environmentally sensitive areas (like water management, forestry, and nature reserves). Modern bio-oils are mostly ester-based. Saturated esters have a longer service life and are more energy-intensive to produce, hence higher in cost — but they often outperform regular mineral oils.

Hydraulic oils are also categorized by viscosity (fluid thickness), expressed as ISO VG (Viscosity Grade) such as 32, 46, or 68. There are also special-purpose oils, like fire-resistant hydraulic oil (for steel mills or underground mining) and food-grade oil (for food production environments).

Viscosity: what do ISO VG 15, 22, 32, 46 and 68 mean?

The ISO VG value of hydraulic oil indicates its thickness (viscosity) at 40°C. The higher the number, the thicker the fluid. ISO VG 15, 22, and 32 are typically used in light, fast-switching hydraulic systems. ISO VG 46 is common for outdoor equipment (like excavators and cranes), while ISO VG 68 is preferred in heavier systems or where higher temperatures and loads occur. The machine manufacturer determines the correct viscosity class because they know the exact operational forces and temperatures. Follow their guidance to avoid system malfunctions. Typically, the pump type determines the viscosity choice.

Oil that is too thin increases wear, risk of leakage, and power loss. Oil that is too thick slows the system and increases energy use. In practice, choosing the right oil based on machine specifications and working climate is crucial. In Europe, ISO VG 32, 46, and 68 are the most widely used in industrial applications.

Which hydraulic oil do I need for my excavator?

This is a question we are often asked. For excavators, loaders, and other earthmoving machines, manufacturers typically recommend a high-quality mineral hydraulic oil with excellent oxidation stability and strong anti-wear properties. The most commonly used is ISO VG 46 (often referred to as HVLP 46 or HLP 46). For excavators, it is recommended to use a hydraulic oil with a high viscosity index — DIN HVLP instead of DIN HLP — since outdoor temperatures can vary significantly by season.

In hotter climates or under heavier loads (e.g., prolonged summer work or industrial applications), ISO VG 68 or similar is required. Always refer to the user manual or service guide of your machine: manufacturers like Caterpillar, Hitachi, Liebherr, and Volvo clearly state the required viscosity and specification — such as DIN 51524 HLP/HVLP, ISO HM/HV, or brand-specific standards. Some brands even recommend using motor oil as hydraulic oil. That’s not a bad idea, as it may offer certain advantages over traditional hydraulic oils. If in doubt, consult OlieOnline experts. Using the wrong oil can quickly lead to malfunctions and damage, and may void your warranty.

Ask OlieOnline experts for advice if you’re unsure — they will help explain the differences. As we always say: Knowledge is our strength!

How often should hydraulic oil be changed in a hydraulic system?

The oil change interval depends on several factors: operating intensity, system load, environmental conditions (dust, moisture, temperature fluctuations), base oil type, brand quality, and maintenance practices. In industry, the following guidelines are common for mineral-based hydraulic oil:

• Heavy-duty machines: every 2,000 to 4,000 operating hours
• Standard-duty machines: every 3,000 to 8,000 hours
• Agricultural or construction machines used intermittently: at least once per year, or every 2 years maximum — or earlier if there are warning signs (such as discoloration, odor, or foaming).

Visually inspect your oil regularly for color and clarity, or — if possible — have it tested annually in a lab. Good oil management prevents up to 80% of hydraulic failures, based on OlieOnline’s experience.

If your systems are large enough, we can arrange oil analysis. Important: Many manufacturers specify exact service intervals — always follow these closely to maintain warranty coverage!

What are the characteristics of a high-quality hydraulic oil?

A good hydraulic oil combines the following properties:

• Optimal viscosity and viscosity index: stable performance across a wide temperature range
• High oxidation stability: slows aging and prevents sludge or varnish deposits
• Excellent anti-wear performance
• Strong protection against rust, corrosion, and foaming
• Efficient air release (trapped air can cause cavitation)
• Effective water separation and good filterability
• Compatible with sealing materials such as NBR, FKM, and PU

Globally recognized brands invest in R&D and choose premium base oils and additive technologies (anti-wear, oxidation, and rust inhibitors). The quality and quantity of these additives directly impact maintenance costs and the lifespan of hydraulic components.

Can I mix different types of hydraulic oil?

Mixing different hydraulic oils is strongly discouraged by manufacturers and specialists. The reason is that the quality and condition of the existing oil are often unknown.

Combining oils based on different base stocks must be avoided (e.g., mixing mineral oil with synthetic or bio-based oil). The additive systems may be incompatible, leading to chemical reactions or sediment formation.

In emergency situations (e.g., breakdowns or urgent repairs), mixing may be unavoidable. Only do so with oils that meet the same specifications, and flush the system as soon as possible. Never mix zinc-containing oils with ashless (zinc-free) hydraulic oils — chemical incompatibility can cause wear and system failure. Differences in color or smell may also indicate incompatibility.

What should I consider when buying hydraulic oil?

When purchasing hydraulic oil, always consider the following:

• Price vs. quality: cheap oil often results in higher wear and operational costs. Choose a globally recognized brand.
• Viscosity/class (ISO VG 15, 22, 32, 46, 68): must match system, pump type, and climate.
• Standards/certifications (e.g., DIN 51524, ISO 11158): always follow your machine’s recommendation.
• Application: standard, fire-resistant, biodegradable, or food-grade oil.

Ask OlieOnline experts for advice if in doubt — we’re here to help you understand the differences. As we say: Knowledge is our strength!

What are the consequences of using the wrong hydraulic oil?

Using the wrong hydraulic oil (wrong viscosity, additives, or type) can have immediate and serious consequences:

• Accelerated wear of pumps, valves, cylinders, and bearings
• Increased leakage and/or pressure loss
• Damage from cavitation or excessive energy consumption
• Formation of foam, sludge, or varnish
• Clogging of filters and pipes due to faster contamination
• Warranty may be void if incorrect oil use is proven
• The system may eventually seize completely, requiring expensive repairs

Example from the field: if oil that’s too thin is used in a forklift or loader, it may not lift properly (insufficient pressure build-up), and internal wear increases. If the oil is too thick, movements become sluggish and energy use rises.

How can I tell if my hydraulic oil needs replacing?

Old or contaminated hydraulic oil can be recognized by:

• Discoloration — brown, black, milky, or cloudy appearance
• Strong, unusual smell (burnt or rancid)
• Increased foaming or air entrapment
• Reduced system responsiveness (slower, louder, or irregular)
• Filters clogging more frequently
• Lab analysis showing high wear metals, depleted additives, or water contamination

Quick test: place a drop of oil on a white tissue. If you see visible metal particles, muddy or dark color, or a strange smell, change the oil immediately. For professional or high-value systems, periodic lab analysis is essential for predictive maintenance and to avoid unexpected downtime.

Frequently Asked Questions (Hydraulic Oil FAQ)

What types of viscosity grades are available?

The ISO VG standards range from 15 to 460. For most hydraulic applications, ISO VG 15, 22, 32, 46, 68, and 100 are the most commonly used grades.

How is hydraulic oil classified?

Based on ISO/DIN standards: ISO HM and HV (DIN HLP/HVLP). HM/HLP is standard mineral oil; HV/HVLP includes viscosity index improvers for better performance in temperature fluctuations.

Can I use engine oil as hydraulic oil?

In some cases, yes — if the excavator manufacturer explicitly allows it. Normally, engine oil is not suitable for hydraulic systems due to different compositions and additives and may cause damage.

Are biodegradable hydraulic oils just as good?

Yes, they are — but they require more attention when it comes to filtering and moisture control. The presence of water breaks down the oil — this is how it "knows" it has entered the environment.

Does changing the oil more often help prevent clogging?

Yes, timely oil changes help prevent deposits and extend service life (and help avoid 80% of failures).

How should hydraulic oil be stored?

In a dry, frost-free area, in its original sealed packaging and out of direct sunlight — this prevents quality loss.

Where does the quality difference in hydraulic oils come from?

OlieOnline always recommends choosing a globally recognized brand. These companies have the resources for extensive research and cannot afford reputation damage. What matters is that the oil’s protective properties are guaranteed under all speeds and conditions. Not every hydraulic oil delivers this! A major quality difference lies in how LONG and how EFFECTIVELY the oil maintains its performance.

Often, you don’t immediately notice when your oil quality has degraded. Most wear and damage is only discovered afterwards — and you may not realize the cause was poor hydraulic oil.

What is the influence of temperature on hydraulic oil?

Some hydraulic oils have better viscosity stability, meaning they thin out less at high temperatures and remain fluid at low temperatures. High heat accelerates wear. An oil cooler can be a smart investment — but always consider the quality of the hydraulic oil you’re buying.

At high temperatures, carbon particles may form — especially in aged or low-quality oil. These particles can settle on internal parts such as valves and pump components, causing major issues. The quality of the base oil and additive package determines how long the hydraulic oil remains effective.

What is HLP oil?

HLP is a DIN standard. DIN HLP defines the minimum requirements for indoor-use hydraulic oil. Generally, globally recognized brands exceed this HLP standard — but this says nothing about how long the oil will maintain its performance.

Practical examples, statistics, and hydraulic system failures

Hydraulic systems are found in airplanes, excavators, bridges, factories, and even car lifts. Pressure levels vary by application: aircraft often use hydraulic fluid at over 3,000 psi (200+ bar), while presses and lifts can exceed 500–700 bar. According to OlieOnline’s experience and research, around 80% of all hydraulic failures are caused by contaminated or incorrect oil. With proper oil management and routine inspections, most of these costly failures can be prevented.

At NASA, the space shuttle’s hydraulic pumps ran at 3,600 RPM and delivered about 3,050 PSI — a great example of how crucial high-performance oil is under extreme conditions.

In practice: a hydraulic pump in a heavy crane running on ISO VG 46 with viscosity improvers will last significantly longer under normal weather conditions than if thinner ISO VG 32 oil is used.

Every 10°C increase in temperature doubles the rate of oxidation. So an oil cooler can add significant value when temperatures rise.

Hydraulic oil maintenance and change intervals

Regular maintenance and timely oil changes are essential for hydraulic system performance and longevity. Contamination, aging, and temperature fluctuations degrade oil quality — leading to wear and inefficiency.

Maintenance tips:

• Check oil levels regularly.
• Analyze oil for contamination.
• Use filters to keep the oil clean.
• Change the oil according to the manufacturer’s recommendation.

Innovations in hydraulic oil

With advancing technology, synthetic hydraulic oils are now available that perform better in extreme temperatures, allow longer drain intervals, and improve machine energy efficiency. These oils contain advanced additives that reduce wear and support extended component life.

Below are more hydraulic fluid classifications:

Specialist hydraulic oil advice

We understand it can be overwhelming with over 100 types of hydraulic oil available — especially if you're not familiar with them. Always start by consulting your machine's manual, as we will ask what is stated there! Once that's clear, seek detailed advice to ensure performance and equipment reliability.

We are your hydraulic oil specialists. If you're unsure, don’t worry — we have the knowledge and expertise to give you personal advice tailored to your machine, working conditions, and expected oil service life.

The right hydraulic oil

Specific hydraulic oils are available for hydraulic systems — and you can order them from OlieOnline. Using the right oil ensures performance, service life, and protection.

Order your hydraulic oil from OlieOnline

At OlieOnline, you’ll find the best hydraulic oils from globally recognized quality brands. Knowledge is our strength! We understand the technology and can advise you across a wide range of options. Quantities are listed in the product descriptions — and for bulk oil orders, we’re happy to discuss your needs personally.

Still not sure which hydraulic oil to choose? You’re welcome to contact our specialists. For more information about hydraulic oil — or any other lubricants — don’t hesitate to get in touch. We’re happy to help.

Corrosion and wear

When hydraulic components such as pumps, cylinders, or motors fail, it can be very costly — and often unplanned. The link to poor oil quality is rarely made. Friction causes wear despite lubrication. A good hydraulic oil reduces friction, which lowers both temperature and wear.

Perform regular maintenance and drain condensation water. If this is not possible, consider a moisture-absorbing hydraulic oil. This so-called dispersant hydraulic oil will help protect your equipment against corrosion and wear.

Hydraulic oil stress

The use of hydraulic oil depends on machine design, application, and pressure levels. Machines are becoming more powerful — but reservoirs are smaller. This increases stress on the oil. In areas with large temperature fluctuations, it’s smart to select a hydraulic oil with a high viscosity index (VI).

HVLP oils resist viscosity changes under varying temperatures, offering better protection in both cold and hot conditions. Protect your system against overheating with a properly selected high-quality hydraulic oil.

The environment affects hydraulic oil

Many hydraulic systems operate in dusty or sandy conditions. This contamination enters the system, so filtration is essential. Hydraulic oil must be highly filterable. Manufacturers like Caterpillar, Komatsu, Terex, and sometimes Liebherr, recommend using engine oil instead of hydraulic oil for some models.

Do you work in an environmentally sensitive area? OlieOnline offers a wide range of biodegradable hydraulic oils. Feeling overwhelmed? That’s why we always say: hydraulic oil is the most underrated lubricant!

Where can I buy hydraulic oil?

Buying hydraulic oil is easy online! With expert advice from OlieOnline, you’ll choose the right oil and avoid unpleasant surprises. Already know which one you need? You can order directly on our website.

Our product range includes a wide variety of hydraulic oils in small (20 liter) and large volumes (1000 liters or bulk). Ordering is easy and fast. Prefer to go through the order with one of our staff to make sure it’s correct? We’re happy to help you by phone or email.

Summary & Conclusion

Hydraulic oil is the lifeblood of any hydraulic system — from agricultural and construction machinery to heavy industry. Invest in the right oil with attention to viscosity, specification, and classification. Check and change your oil regularly, and watch for signs of aging or contamination.

Hydraulic oil is essential for proper system performance. By choosing the right oil and performing regular maintenance, you’ll reduce downtime, wear, and inefficiency. Whether you choose mineral or synthetic, make sure the specifications match your equipment’s requirements and work environment. This not only optimizes performance — it also extends equipment life significantly.

Always follow the manufacturer’s recommendations, choose global quality over price, and consult a specialist when in doubt. This helps prevent costly breakdowns, wear, and unexpected failures. Correct oil use, maintenance, and monitoring can save thousands per year — and ensure a safe, sustainable, and efficient operation. Still have questions? Contact us — we’re here to help!