The Impact of Viscosity Index on Hydraulic System Efficiency

Keeping hydraulic systems running smoothly isn’t just about having oil — it’s about having the right oil. And one factor that often gets overlooked is the viscosity index (VI). This number tells us how an oil’s thickness changes with temperature, and it can make a big difference in efficiency, performance, and equipment life. 

Too thick or too thin, and your pumps and valves can struggle, overheat, or wear out faster. At Fubex Lubricants, we offer high-quality hydraulic oil for all types of engines. Enjoy fast shipping, a price match guarantee, and no-questions-asked returns. Need help choosing the right oil? Call us at +971 50 544 9614 — our friendly team is ready to assist!

Awais I., Sales Director, says, ‘‘At Fubex Lubricants, our hydraulic oils keep machines running smoothly, protect against wear and rust, and ensure reliable performance every day.’’

In this article, we’ll explore why viscosity index matters and how choosing the right hydraulic oil can keep your system performing at its best, every time.

What Is the Viscosity Index of Engine Oil?

The viscosity index (VI) of an engine oil shows how much the oil’s thickness changes when the temperature goes up or down.

Here’s an easy way to remember it:

• When the temperature increases, the oil becomes thinner.
• When the temperature drops, the oil becomes thicker.

This means that the way an oil is made — its formula and quality — is very important. A good-quality oil will not get too thin when it’s hot or too thick when it’s cold.

The viscosity index tells you how stable the oil’s thickness stays with temperature changes. Oils with a high VI work better in engines because they can handle both hot and cold conditions without losing their performance. So, knowing the VI helps you choose the right oil for your engine’s temperature range.

How Is the Oil’s Viscosity Index Measured?

To find an oil’s viscosity index, experts measure how fast it flows (called kinematic viscosity) at 40°C and 100°C. These results are then compared to two standard reference oils.

Here’s a quick comparison:

• Regular mineral oils have a VI between 95 and 100.
• Refined mineral oils (hydrotreated) can reach around 120.
• Hydrocracked and synthetic oils often have a VI above 120, with some synthetics going up to 140.
• Naphthenic oils have the lowest VI, around 80.

In short, the higher the viscosity index, the better the oil can handle temperature changes — keeping your engine protected and running smoothly.

How Fluid Viscosity Affects Hydraulic Systems

Hydraulic systems use special fluids to move power and keep everything running smoothly. The viscosity of that fluid — which means how thick or thin it is — plays a big role in how well the system works. Let’s break down how it affects different parts of the system.

Mechanical Efficiency

Mechanical efficiency means how well the fluid reduces friction between moving parts inside the system.

• If the oil is too thick (high viscosity), it moves slowly and causes more friction.
• This makes the system sluggish, reduces speed, and can cause wear or even failure over time.

To work smoothly, the hydraulic fluid needs to be just the right thickness — not too thick and not too thin.

Volumetric Efficiency

Volumetric efficiency is about how much power is lost inside the system.

• If the oil is too thin (low viscosity), it can easily slip through small gaps inside pumps and valves.
• This causes leaks inside the system, lowers pressure, and wastes energy.
• The system becomes less responsive and heats up faster, which shortens the life of the parts.

So, oil that’s too thin means less power and more wear.

Hydrodynamic Lubrication

Hydrodynamic lubrication (also called fluid film lubrication) happens when a thin layer of oil separates moving parts so they don’t touch directly.

• If the oil is too thin, the film becomes too light, and parts can rub together.
• If it’s too thick, it causes extra friction and heat.

This is similar to how a car slides on water when the road is wet — the oil layer acts like that water, keeping parts from touching. The key is balanced viscosity to protect parts without slowing the system down.

Cavitation

Cavitation happens when the oil supply can’t keep up with the system’s speed. This creates tiny air bubbles (cavities) that collapse quickly, damaging metal surfaces.

• Thick oils (high viscosity) move slowly, making it easier for cavitation to happen.
• This can cause metal erosion, heat, and loss of lubrication.

Using oil with the right flow rate helps prevent cavitation problems.

Heat Dissipation

Hydraulic fluids also help carry away heat from the system.

• As oil heats up, it becomes thinner, which can reduce its ability to protect parts.
• That’s why it’s important to use an oil with a high viscosity index (VI) — it stays more stable at different temperatures.

High VI oils can absorb and transfer heat better without losing their key properties.

Air Release

Air release means how quickly the oil can let trapped air escape.

• If air stays in the oil, it causes poor performance, noise, and cavitation.
• Thicker oils hold onto air bubbles longer — just like honey traps bubbles more than water does.

To fix this, systems may use larger tanks to give air time to escape before the oil moves through again.

Filtration Ability

The filtration ability of hydraulic oil shows how well it passes through filters that clean out dirt and debris.

• Filters create a bit of pressure when oil flows through them — this is called pressure drop.
• Thicker oils are harder to push through filters, causing a higher pressure drop.

That’s why the right viscosity helps keep both the oil clean and the system efficient.

In Short

Getting the right viscosity in hydraulic fluid is super important.

• If it’s too thick, the system becomes slow and wastes energy.
• If it’s too thin, the system loses power and wears out faster.

Using high-quality hydraulic oils with the right viscosity — like those from Fubex Lubricants — helps your hydraulic system run smoothly, stay cool, and last longer.

Why Hydraulic Fluid Viscosity Is So Important

The viscosity of hydraulic fluid — how thick or thin it is — plays a huge role in how well your hydraulic system works. It’s not as simple as it seems because viscosity affects many parts of the system at once.

To choose the right hydraulic oil, you need to think about how your system operates — including its temperature, pressure, and working conditions.

If the oil’s viscosity is too low, it won’t protect the parts well. If it’s too high, the system will run slowly and waste energy.

That’s why it’s important to pick a fluid with the right viscosity for your system’s temperature range. In places with very hot or cold conditions, you may need a higher viscosity oil to keep everything running smoothly and efficiently.

Choosing the Right Hydraulic Oil for Your System: Our Top Picks

Discover the best hydraulic oils that keep your machines running stronger, longer, and smoother in any condition. Dive in to see our top picks and find the perfect Fubex oil for your system’s peak performance!

Fubex HYDRO AW ISO VG-10W

One of our most trusted hydraulic oils is the Fubex HYDRO AW ISO VG-10W, and for good reason. It’s built to deliver lasting performance, protect against rust, and keep your system safe from water damage. This oil keeps your hydraulic pumps running smoothly, even under high heat. With excellent foam control and filter compatibility, it’s the smart choice for powerful, reliable performance.

Fubex HYDRO AW ISO VG-15 Hydraulic Oil

The Fubex HYDRO AW ISO VG-15 is a customer favorite — and it’s easy to see why. Built for heavy-duty machines and gearboxes, it delivers unbeatable protection in tough conditions. It resists foam, heat, and pressure to keep your equipment running smoothly. With strong anti-rust power and leak prevention, it’s the ultimate choice for total hydraulic protection.

Fubex HYDRO AW HVI SYN ISO VG-22

The Fubex HYDRO AW HVI SYN ISO VG-22 is engineered for power, stability, and long-lasting performance. Designed to stay strong under pressure, it keeps pumps running smoothly in both hot and cold conditions. Its high-viscosity formula resists breakdown, even in extreme heat or heavy use. Perfect for hydraulic systems and gearboxes, it delivers unmatched protection and reliability.

Fubex HYDRO AW HVI SYN ISO VG-10W

The Fubex HYDRO AW HVI SYN ISO VG-10W is built for performance in every condition. It keeps hydraulic systems running smoothly, even in freezing or changing temperatures. Designed to resist wear, rust, and foam, it delivers lasting protection for heavy-duty equipment. Whether on or off the road, this oil ensures powerful, clean, and reliable operation.

Fubex HYDRO AW HVI ISO VG-10W

The Fubex HYDRO AW HVI ISO VG-10W stands out for its clean, high-quality formula and powerful protection. Designed for machines that face wide temperature changes, it keeps performance steady and reliable. Its advanced anti-wear and anti-rust additives guard every part from damage. With fast water separation and anti-foam control, it ensures smooth, precise hydraulic operation every time.

Fubex HYDRO AW HVI ISO VG-46

The Fubex HYDRO AW HVI ISO VG-46 is a high-performance anti-wear hydraulic oil built for heavy-duty systems. Its strong formula protects parts from wear and keeps the oil stable, even under extreme temperatures. With excellent anti-foam and oxidation resistance, it ensures smooth and reliable operation. Perfect for hydraulic circuits, controls, and regulation systems, it delivers consistent performance under heavy loads.

Other Important Performance Characteristics

The viscosity index (VI) of a hydraulic fluid shows how its thickness changes when the temperature goes up or down. Fluids with a higher VI stay more stable in different temperatures, which makes them more efficient and reliable.

But viscosity index isn’t the only thing that matters. For the best performance, hydraulic fluids need several other important qualities too. Let’s look at them one by one.

• Wear Resistance: This means the fluid can protect metal parts from rubbing and wearing out. Fluids with anti-wear additives form a thin protective layer that helps parts last longer.
• Oxidation Stability: When oil gets hot, it can react with oxygen and break down. Fluids with antioxidant additives resist this, helping the oil last longer and keeping costs lower.
• Thermal Stability: Good hydraulic oil can handle high temperatures without breaking down. This prevents problems like sludge, varnish, and clogged filters that can slow down the system.
• Hydrolytic Stability: Sometimes water can get into the hydraulic system. Fluids with strong hydrolytic stability resist damage from water, stopping the formation of acids and sludge that harm the system.
• Demulsibility: This means the oil can separate from water easily. That way, the water can be removed before it causes rust or performance issues.
• Rust and Corrosion Protection: Hydraulic fluids need additives that prevent rust on metal parts. This keeps both the oil and the equipment clean and free of corrosion.
• Foam Inhibition: When air mixes with oil, it can create foam, which reduces the oil’s ability to protect the system. Fluids with foam inhibitors prevent this problem and keep performance smooth.
• Compressibility: Good hydraulic oil should not compress easily. Low compressibility helps prevent valve failure, power loss, and cavitation, especially in high-pressure systems.
• Filterability: Hydraulic oil must flow easily through filters to remove dirt and debris. Fluids with dispersant additives stop sludge from forming, keeping the system clean and efficient.
• Seal Compatibility: The oil must work well with different rubber seals in the system. If it doesn’t, seals can swell or leak, leading to performance issues.

A high-performance hydraulic fluid must balance all these features — not just viscosity. Oils like Fubex Hydraulic Fluids are designed with the right additives to give strong protection, smooth operation, and long-lasting performance.

When choosing the best hydraulic oil, always look beyond the viscosity index and consider all these factors to keep your equipment working at its best.

FAQs

Q1: How to extend the life of hydraulic oil with filtration

To make hydraulic oil last longer, keep it clean with filters and check it regularly. Follow a maintenance schedule and watch for leaks to prevent contamination.

Q2: Why anti-wear hydraulic oils are vital for excavators

Anti-wear (AW) hydraulic oils help excavator parts slide smoothly, reducing wear on pumps, cylinders, and valves. They keep the system running longer, prevent breakdowns, and stop rust, sludge, and overheating.