Hydraulic Oil 46 vs 68: Start With the Equipment Requirement
ISO VG 46 and ISO VG 68 are two common hydraulic-oil viscosity grades, but they are not interchangeable by default. The correct choice depends on the hydraulic system design, pump requirements, operating temperature and the equipment manufacturer’s specification.
Always start with the machine manual or OEM lubricant recommendation before changing viscosity grade.
What Do ISO VG 46 and ISO VG 68 Mean?
The ISO VG number refers to the oil’s nominal kinematic viscosity at 40°C. ISO VG 68 is thicker than ISO VG 46 at the same temperature.
A thicker oil is not automatically better. Excessive viscosity can increase resistance and affect cold-start flow, while an oil that is too thin may reduce film strength or leakage control in some systems.
When Is ISO VG 46 Commonly Used?
ISO VG 46 is widely used in hydraulic systems where the manufacturer specifies this viscosity grade and where operating temperatures suit it. Typical applications can include industrial machinery, mobile equipment and construction systems.
When Is ISO VG 68 Commonly Used?
ISO VG 68 is often specified for systems operating at higher temperatures or where the equipment manufacturer requires a higher-viscosity hydraulic fluid. The actual requirement still depends on the pump, clearances and system design.
Factors to Check Before Choosing
- Equipment or machine manufacturer recommendation
- Hydraulic pump type and viscosity requirement
- Ambient and operating temperature
- System pressure and duty cycle
- Existing oil specification
- Required anti-wear, oxidation and corrosion performance
- Compatibility with seals and previously used fluid
Can You Mix ISO VG 46 and ISO VG 68?
Mixing different hydraulic oils should not be treated as a normal viscosity-adjustment method. Different products may use different additive systems or base oils. If a change is required, follow the equipment and lubricant manufacturer’s changeover recommendations.
Hydraulic Oils Available from INER-G
INER-G supplies hydraulic fluids for industrial, construction and agricultural applications, including ISO VG 46 and ISO VG 68 options from several ranges.
For equipment applications, also see our Agriculture & Construction solutions.
What Information Should You Provide?
For faster product selection, provide the machine make and model, hydraulic system or pump information, the viscosity grade specified in the manual, operating temperature and the currently used oil reference.
Contact INER-G for Hydraulic Oil Selection Support »
Frequently Asked Questions
Is ISO VG 68 always better in hot weather?
No. Ambient temperature matters, but the correct viscosity must remain within the equipment manufacturer’s permitted range.
Can I replace hydraulic oil 46 with 68?
Only if the equipment manufacturer permits the change for the actual operating conditions.
What does ISO VG mean?
ISO VG is a viscosity classification system for industrial lubricants based on nominal kinematic viscosity at 40°C.
Prepared by the INER-G Technical Team. Product selection should always be verified against the equipment manufacturer’s current requirements and the product technical data.