05/06/2026 by Jay Hatton
Choosing the proper hydraulic oil viscosity is vital for operators maintaining hydraulic machinery who are charged with lubricant procurement.
To keep hydraulic motors, pumps, valves and cylinders in hydraulic systems protected and operating effectively, equipment needs the correct oil. Deploying a lubricant with the wrong viscosity grade can cause several unwanted outcomes, including increased component wear, system overheating and inefficient operations.
Here, we compare two of the most used hydraulic oils – ISO VG 32 and ISO VG 46 – and define the conditions in which each is a suitable option.
What is ISO VG 32 hydraulic oil?
ISO VG 32 hydraulic oil is a premium, low-viscosity lubricant designed to transfer power efficiently within hydraulic systems.
ISO VG stands for “International Standards Organisation Viscosity Grade”, while the number 32 refers to the oil’s kinematic viscosity at 40°C, measured in centistokes.
It is formulated to protect against rust, wear and foaming, helping hydraulic systems deliver fast response times in industrial and mobile equipment.
What is ISO VG 46 hydraulic oil?
ISO VG 46 hydraulic oil is a premium mineral-based lubricant with a medium viscosity, designed for hydraulic systems that require a heavier-duty oil.
The number 46 refers to its kinematic viscosity at 40°C, which is the standard reference temperature used globally to classify the thickness of hydraulic oils.
When to use ISO VG 32 hydraulic oil
ISO VG 32 is a thinner hydraulic oil that flows more freely. As a result, it pressurises faster when systems start up. This property is critical in colder operating conditions, when thicker oil can cause lubrication starvation in pumps for the first critical seconds of operation.
This viscosity grade is suitable for a range of indoor equipment, including industrial presses, machine tools and factory automation systems, where machinery is designed to keep oil temperature controlled and ambient temperatures are regulated.
Pallet trucks and forklifts working in refrigerated warehouses and cold storage facilities can also benefit from its coveted characteristics, as can outdoor equipment for cold climate use, such as gritters and snow ploughs.
ISO VG 32 is also suitable for low pressure and smaller systems when a pump OEM (Original Equipment Manufacturer) recommends a lower viscosity range.
It is important to remember that ISO VG 32 creates a thinner oil film at higher temperatures. In hydraulic systems that generate significant heat under heavy loads, the oil can become too thin, increasing the risk of metal-on-metal contact and premature wear.
When to use ISO VG 46 hydraulic oil
Today, ISO VG 46 is the world’s most used hydraulic oil. It is recognised as the go-to oil grade for most mobile plant equipment, and the specific hydraulic oil grade OEM manuals advise for general outdoor use in both warm and temperate climates.
Consequently, it is suitable for diggers, dump trucks and excavators, but also sees frequent use maintaining wood chipping and log splitting equipment, among other high pressure outdoor machinery. As an agricultural oil, it lubricates and transfers power in combine harvesters, tractors and telehandlers working in spring and summer months, and warmer climates generally.
Overall, it is ideal for any hydraulic systems running consistently at ambient temperatures over 10°C. Its thicker viscosity means it maintains a more robust oil film at higher operating temperatures, which directly translates to enhanced valve and pump protection working under sustained high-pressure and loads.
Key differences between ISO VG 32 and 46 hydraulic oil
The main difference between ISO VG 32 and 46 is their viscosity. ISO VG 32 is a much thinner fluid, which means it can perform effectively during cold starts and in low pressure applications.
ISO 46 is thicker, which means it can work properly under higher loads and in warmer environments without the protective film it provides breaking down.
For high-quality ISO VG grade oils from top brands like Kluber, Morris and Petronas, browse our products at Oil Store today.
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