Gearbox Oil Explained: ISO VG 220 vs 320 vs 460 – Which Oil Does Your Gearbox Need?

Choosing the correct gearbox oil is one of the simplest ways to protect an industrial gearbox, reduce wear, control temperature and extend service life. The problem is that many gearbox labels simply show terms like ISO VG 220, ISO VG 320 or ISO VG 460, without clearly explaining what those numbers actually mean.

This guide explains the difference between ISO VG 220, 320 and 460 gearbox oil, when each grade is normally used, and why the correct lubricant matters for worm gearboxes, inline gearboxes, helical bevel gearboxes and complete motor gearbox assemblies.

What Does ISO VG Mean in Gearbox Oil?

ISO VG stands for International Standards Organisation Viscosity Grade. It is a way of classifying industrial oils by their viscosity, which means how thick or resistant to flow the oil is.

The number after ISO VG is linked to the oil’s approximate kinematic viscosity at 40°C. For example:

• ISO VG 220 is thinner than ISO VG 320 and ISO VG 460.
• ISO VG 320 is thicker than ISO VG 220 but thinner than ISO VG 460.
• ISO VG 460 is the thickest of the three and gives a heavier oil film.

In simple terms, the higher the ISO VG number, the thicker the oil. Thicker oil can provide a stronger lubricating film under heavy loads, but it can also create more drag, more churning losses and harder cold starts if it is too thick for the gearbox.

ISO VG 220 vs 320 vs 460: Simple Comparison

This is why you should never choose gearbox oil by viscosity alone. You also need to consider gearbox type, gear material, load, speed, operating temperature and whether the unit needs mineral, synthetic, EP, compounded or worm-drive-specific oil.

Why Gearbox Oil Matters So Much

Inside a gearbox, the oil has several important jobs. It must separate the gear teeth, protect bearings, reduce friction, carry heat away from the gear mesh, resist foaming, prevent corrosion and protect the internal components during start-up and continuous running.

If the oil is too thin, the oil film may not be strong enough under load. If the oil is too thick, the gearbox can run hotter because the gears have to churn through a heavier lubricant. Both problems can shorten gearbox life.

Correct oil selection is especially important on industrial applications such as conveyors, mixers, packaging lines, pumps, fans, lifting equipment and processing machinery. If you are selecting a complete drive package, it is worth matching the gearbox correctly with the right AC motor, mounting style and service factor from the beginning.

Which Gearbox Oil Should You Use?

The correct gearbox oil depends on the gearbox manufacturer’s specification first. If the gearbox nameplate, manual or datasheet states ISO VG 320, then ISO VG 320 is normally the starting point. If it states ISO VG 460, do not downgrade to ISO VG 320 unless the manufacturer confirms it is acceptable.

As a general guide:

• Use ISO VG 220 where the manufacturer specifies it, or where the gearbox is relatively small, higher speed, lightly loaded or operating in cooler ambient temperatures.
• Use ISO VG 320 where the manufacturer specifies it, or where the gearbox needs a balanced industrial gear oil for normal enclosed gearbox service.
• Use ISO VG 460 where the manufacturer specifies it, or where the gearbox is slower, more heavily loaded, larger, hotter-running or needs a stronger oil film.

For replacement gearboxes, always check the original manufacturer’s oil recommendation before filling the unit. This is particularly important when replacing older units with modern industrial gearboxes, because oil type and viscosity can vary between brands and gearbox designs.

Worm Gearbox Oil: Why It Needs Extra Care

Worm gearboxes need special attention because they usually have a high sliding action between the worm shaft and the worm wheel. Many worm gearboxes also use a steel worm with a bronze or bronze-alloy worm wheel.

This means oil choice is not only about ISO VG viscosity. The additive package also matters. Some general industrial EP gear oils are designed for spur, helical, bevel or steel-on-steel gearing, but may not be the correct choice for bronze worm wheels unless the oil manufacturer and gearbox manufacturer confirm compatibility.

For worm gearboxes, you may see recommendations for:

• Compounded worm gear oil for sliding worm gear contact.
• PAG synthetic worm gear oil for higher efficiency and better performance in certain worm drives.
• ISO VG 320 or ISO VG 460 depending on the gearbox size, ratio, load and operating temperature.

If you are buying or replacing a worm gearbox, check the lubricant requirement for the specific unit. This applies to ranges such as Motovario NMRV worm gearboxes, Varvel worm gearboxes, Tramec worm gearboxes and Bonfiglioli worm gearboxes.

ISO VG 220 Gearbox Oil: When Is It Used?

ISO VG 220 is a lower-viscosity industrial gearbox oil compared with ISO VG 320 and ISO VG 460. It flows more easily, which can be useful in smaller gearboxes, faster-running units or cooler operating environments.

ISO VG 220 may be suitable where:

• The gearbox manufacturer specifically recommends ISO VG 220.
• The gearbox is running at a relatively high input speed.
• The load is moderate rather than heavy shock load.
• The gearbox is operating in cooler ambient conditions.
• The unit needs reduced drag or better cold-start flow.

However, ISO VG 220 can be too thin for some slower, heavily loaded or hot-running gearboxes. If a worm gearbox or large industrial reducer specifies ISO VG 320 or ISO VG 460, using ISO VG 220 may reduce the oil film strength and increase the risk of wear.

ISO VG 320 Gearbox Oil: The Common Middle Ground

ISO VG 320 is a common industrial gear oil grade because it sits between ISO VG 220 and ISO VG 460. It is often used where the gearbox needs a stronger oil film than ISO VG 220, but without the extra thickness of ISO VG 460.

ISO VG 320 may be suitable where:

• The gearbox manufacturer specifies ISO VG 320.
• The unit is a general enclosed industrial gearbox.
• The gearbox has moderate load and normal operating temperature.
• The gearbox needs a balanced grade for protection and efficiency.
• The application runs for long periods and stable lubrication is important.

For many industrial users, ISO VG 320 is the grade they see most often on gearbox datasheets and oil charts. But it is still not universal. A gearbox may need ISO VG 220, ISO VG 460, synthetic oil, food-grade oil, worm-drive-specific oil or another grade entirely depending on the design.

ISO VG 460 Gearbox Oil: When Thicker Oil Is Needed

ISO VG 460 is thicker than ISO VG 320 and is normally used where the gearbox needs a heavier lubricating film. This can be useful in slower-speed, high-load or hotter-running applications.

ISO VG 460 may be suitable where:

• The gearbox manufacturer specifies ISO VG 460.
• The gearbox is larger or more heavily loaded.
• The gearbox runs at lower output speed with higher torque.
• The unit operates in a warmer environment.
• The gearbox has high sliding contact, such as certain worm gear applications.

The danger is using ISO VG 460 where it is not needed. Oil that is too thick can increase drag, raise operating temperature, reduce efficiency, cause foaming and increase the load on the motor. On a motor gearbox package, this can make the connected conveyor motor work harder than necessary.

How to Choose the Correct Gearbox Oil Grade

Use this checklist before choosing between ISO VG 220, 320 and 460.

1. Check the Gearbox Nameplate or Manual

The manufacturer’s recommendation is the most important starting point. Look for the required ISO VG grade, oil type, fill quantity and any approved lubricant list.

2. Identify the Gearbox Type

Worm gearboxes, inline helical gearboxes and helical bevel gearboxes do not always use the same lubricant type. A helical bevel gearbox may be happy with an approved industrial EP gear oil, while a bronze worm gearbox may need a worm-drive-specific lubricant.

3. Check the Gear Materials

If the gearbox contains a bronze worm wheel, do not assume any generic EP gear oil is safe. Use an oil confirmed as suitable for yellow metals or a worm gear oil recommended by the manufacturer.

4. Consider Load and Shock Loading

Heavy loads, frequent starting, reversing, impact loads and high torque can require a stronger oil film. In some cases, this may point towards a higher viscosity grade or a different oil type.

5. Consider Speed

Higher-speed gearboxes often need oil that flows well and does not create excessive churning losses. Slower, higher-torque gearboxes may require a thicker oil film.

6. Consider Temperature

Oil gets thinner as it gets hotter and thicker as it gets colder. A gearbox running in a warm factory, near process heat or under continuous load may need different oil consideration compared with a gearbox running outdoors in winter.

7. Do Not Mix Oil Types

Do not mix mineral, PAO synthetic, PAG synthetic or food-grade oils unless the lubricant manufacturer confirms compatibility. If switching oil type, the gearbox may need to be drained and flushed properly first.

Signs the Gearbox Oil May Be Wrong

Wrong gearbox oil can create symptoms that look like gearbox failure, motor overload or poor installation. Common warning signs include:

• Gearbox running hotter than normal after an oil change.
• Oil leaks caused by excess pressure, foaming or seal incompatibility.
• Foaming oil visible through the level plug or breather area.
• Noisy operation caused by poor lubrication film or gear wear.
• Higher motor current due to increased gearbox drag.
• Bronze or metallic particles in drained oil.
• Burnt smell or dark oil from overheating or oxidation.
• Short bearing life caused by poor lubricant flow or contamination.

If the gearbox is driving a pump, fan or conveyor, lubrication problems can also affect the connected motor. For example, excess gearbox drag may increase load on pump motors, fan motors or conveyor drive motors.

Gearbox Oil Fill Level: Do Not Overfill the Gearbox

More oil does not automatically mean better lubrication. Overfilling a gearbox can cause churning, foaming, pressure build-up, seal leaks and higher operating temperature.

Most industrial gearboxes should be filled to the correct level plug or oil level mark, depending on mounting position. Mounting position matters because the oil level required for a foot-mounted gearbox may not be the same as a flange-mounted or shaft-mounted unit.

If the gearbox has been installed in a different mounting position from the original specification, check the oil quantity again. The correct oil level is just as important as the correct ISO VG grade.

Mineral vs Synthetic Gearbox Oil

Gearbox oil can be mineral-based or synthetic. Mineral gear oils are widely used in standard industrial gearboxes, while synthetic oils may be chosen for higher temperature stability, longer service intervals, improved efficiency or specialist applications.

Synthetic gearbox oil may be worth considering where:

• The gearbox runs continuously.
• The gearbox operates at higher temperature.
• The unit is difficult to access for maintenance.
• The application needs improved efficiency.
• The manufacturer specifically recommends a synthetic lubricant.

For worm gearboxes, some synthetic PAG oils are designed specifically for bronze-on-steel worm gear contact. However, you should only use them when suitable for the gearbox and seal materials, and you should avoid mixing them with incompatible oils.

Gearbox Oil for Different Gearbox Types

Worm Gearboxes

Worm gearboxes often need special attention because of their sliding gear contact and bronze worm wheel materials. Always check whether the gearbox requires a specific worm gear oil, compounded oil or PAG synthetic lubricant. Shop our worm gearbox range if you need a replacement gearbox or complete drive solution.

Inline Gearboxes

Inline gearboxes typically use helical gearing and may require an approved industrial gear oil suitable for enclosed gear units. Browse our inline gearbox range for compact industrial drive applications.

Helical Bevel Gearboxes

Helical bevel gearboxes are commonly used where efficient right-angle power transmission is needed. Oil selection should follow the gearbox manufacturer’s viscosity and oil type recommendation. View our helical bevel gearbox range for high-efficiency industrial applications.

Motor Gearbox Assemblies

When a gearbox is paired with an electric motor, incorrect oil can increase drag and operating temperature. This can affect the complete drive system, not just the gearbox. If you are building a complete package, browse our AC motors and brake motors alongside the correct gearbox selection.

Common Gearbox Oil Mistakes to Avoid

• Using engine oil instead of gearbox oil: Engine oil is not the same as industrial gearbox oil and should not be used unless specifically approved.
• Using automotive gear oil without checking compatibility: Automotive oils may contain additive systems that are not suitable for certain industrial gearboxes.
• Assuming thicker oil is always better: Too much viscosity can cause overheating, drag and foaming.
• Ignoring bronze worm wheels: Some worm gearboxes need oil compatible with yellow metals.
• Mixing oil types: Mineral, PAO, PAG and other oils should not be mixed without confirmation.
• Overfilling the gearbox: Too much oil can be just as damaging as too little oil.
• Ignoring mounting position: Oil level and fill quantity can change depending on how the gearbox is mounted.
• Not replacing breathers or seals: A blocked breather or worn seal can cause leaks and contamination.

Gearbox Oil Change Checklist

Before changing gearbox oil, follow this simple maintenance checklist:

• Confirm the gearbox make, model and ratio.
• Check the manufacturer’s oil grade and lubricant type.
• Confirm whether the gearbox uses mineral, synthetic, PAG, compounded or food-grade oil.
• Check whether the gearbox contains bronze components.
• Drain the old oil while warm, if safe to do so.
• Inspect the old oil for metal particles, water contamination or burnt smell.
• Clean the magnetic drain plug if fitted.
• Replace seals, breathers or plugs if required.
• Refill to the correct level plug, not simply to the top of the gearbox.
• Run the gearbox and recheck for leaks, noise and temperature.

If you need replacement parts, mounting components or related drive accessories, view our gearbox accessories and motor accessories.

Shop Gearboxes by Brand

At Worm Gear Motors Online, we supply a wide range of industrial gearboxes, motors and drive components for replacement, maintenance and new machine builds. Browse our key gearbox ranges below:

• Motovario NMRV Worm Gearboxes
• Varvel Worm Gearboxes
• Tramec Worm Gearboxes
• Bonfiglioli Worm Gearboxes
• Pujol Gearboxes
• Amtecs Gearboxes

FAQs About Gearbox Oil

What is the difference between ISO VG 220 and ISO VG 320?

ISO VG 320 is thicker than ISO VG 220. ISO VG 220 flows more easily and may be used in smaller, faster or cooler-running gearboxes where specified. ISO VG 320 gives a heavier oil film and is commonly used in many industrial enclosed gearboxes where recommended by the manufacturer.

What is the difference between ISO VG 320 and ISO VG 460?

ISO VG 460 is thicker than ISO VG 320. It may be used for slower, heavier-loaded or hotter-running gearboxes where the manufacturer specifies it. However, using ISO VG 460 in a gearbox designed for ISO VG 320 can increase drag, heat and foaming.

Can I use ISO VG 320 instead of ISO VG 460?

Only if the gearbox manufacturer or lubricant supplier confirms it is suitable. ISO VG 320 is thinner than ISO VG 460, so it may not provide enough film strength in gearboxes designed for heavier oil.

Can I use ISO VG 460 instead of ISO VG 320?

Not without checking the manufacturer’s recommendation. Thicker oil is not always better. ISO VG 460 can create extra drag and higher operating temperature if the gearbox was designed for ISO VG 320.

What oil goes in a worm gearbox?

Many worm gearboxes require a specific worm gear oil, compounded oil or synthetic lubricant suitable for sliding contact and bronze gear materials. Always check the gearbox manual, nameplate or approved lubricant list before filling a worm gearbox.

Should a gearbox be filled to the top with oil?

No. Most gearboxes should be filled to the correct level plug or oil level mark. Overfilling can cause foaming, pressure build-up, leaks and overheating.

Can I mix different gearbox oils?

You should avoid mixing gearbox oils unless the lubricant manufacturer confirms compatibility. This is especially important when switching between mineral oil, PAO synthetic oil and PAG synthetic oil.

Final Answer: Which Gearbox Oil Do You Need?

If your gearbox manual states ISO VG 220, use the correct approved ISO VG 220 oil. If it states ISO VG 320, use the correct approved ISO VG 320 oil. If it states ISO VG 460, use the correct approved ISO VG 460 oil.

The most important point is that viscosity is only one part of the decision. You must also check the gearbox type, gear materials, oil base type, additive compatibility, temperature, speed, load and mounting position.

For worm gearboxes, be especially careful. A bronze worm wheel may need a worm-drive-specific oil rather than a general industrial EP gear oil. For inline and helical bevel gearboxes, always follow the manufacturer’s approved lubricant specification.

Need help choosing a replacement gearbox, motor or drive package? Browse our full range of industrial gearboxes, worm gearboxes, inline gearboxes, helical bevel gearboxes and electric motors at Worm Gear Motors Online.