Choosing the correct hydraulic oil viscosity is important for protecting hydraulic pumps, valves and other components while maintaining efficient system performance. The most common hydraulic oil viscosity grades include ISO VG 32, ISO VG 46 and ISO VG 68.
But what is the difference, and which one should you use?
What Does ISO VG Mean?
ISO VG refers to the International Organization for Standardization Viscosity Grade of an industrial lubricant. The number indicates the oil's approximate viscosity at 40°C.
In simple terms, the higher the ISO VG number, the thicker the hydraulic oil.
| Hydraulic Oil Grade | Relative Viscosity | Typical Applications |
|---|---|---|
| ISO VG 32 | Thinner | Cooler environments, mobile equipment, high-speed systems |
| ISO VG 46 | Medium | General industrial and mobile hydraulic systems |
| ISO VG 68 | Thicker | Hot environments, heavy-duty equipment and slower hydraulic systems |
ISO VG 32 Hydraulic Oil
ISO VG 32 is a relatively low-viscosity hydraulic oil. It can be suitable for equipment operating in cooler conditions or hydraulic systems where the manufacturer specifies a lower viscosity.
Its lower viscosity can also help with cold-start performance and systems operating at higher speeds.
ISO VG 46 Hydraulic Oil
ISO VG 46 hydraulic oil is one of the most widely used grades for general-purpose hydraulic applications.
It provides a balance between fluid flow, component protection and operating-temperature performance, making it common in industrial machinery, hydraulic power units, manufacturing equipment and mobile machinery.
ISO VG 68 Hydraulic Oil
ISO VG 68 hydraulic oil is thicker than VG 32 and VG 46. It may be appropriate for equipment operating at higher temperatures or systems where a higher operating viscosity is specified by the manufacturer.
However, using an oil that is too thick can increase resistance to flow, particularly during cold starts.
ISO VG 32 vs 46 vs 68: Which Hydraulic Oil Do I Need?
There isn't one universally "best" hydraulic oil viscosity. The correct grade depends on the equipment manufacturer's specification, operating temperature, hydraulic system design and application.
As a general rule:
- VG 32 → cooler temperatures and systems requiring lower viscosity
- VG 46 → common general-purpose hydraulic applications
- VG 68 → higher temperatures and applications requiring higher viscosity
Always check the machine manufacturer's lubricant specification before changing viscosity grades.
What About Shell Tellus Hydraulic Oil?
For industrial hydraulic applications, Shell Tellus S2 M is one option within Shell's range of hydraulic fluids. The correct viscosity grade should still be selected according to the equipment manufacturer's requirements and operating conditions.
If you're unsure whether you need ISO VG 32, 46 or 68, don't simply choose based on the oil currently in the machine. Confirm the manufacturer's specification first.
Need Help Choosing Hydraulic Oil?
Not sure which hydraulic oil viscosity your equipment requires?
Send LubeLine the machine make and model, application and current lubricant specification, and our technical team can help identify the appropriate hydraulic oil and viscosity grade for your equipment.
Need hydraulic oil for your equipment? Contact LubeLine Distribution for product advice and supply.