Hydraulic Oil ISO VG 46 vs ISO VG 68

Introduction

Hydraulic oil is essential for the safe and efficient operation of hydraulic systems. It transfers power, lubricates pumps and valves, helps control heat, and protects components against wear and corrosion. Among the most commonly used industrial hydraulic oil grades are ISO VG 46 and ISO VG 68. While both are widely used, they are not interchangeable in every application. The key difference is viscosity. ISO VG 68 is thicker than ISO VG 46 at the reference temperature. Choosing between them depends on the hydraulic system design, operating temperature, pump requirements, load, and manufacturer recommendations.

What Does ISO VG Mean?

ISO VG stands for International Organization for Standardization Viscosity Grade.

The ISO VG system classifies industrial lubricating oils according to their kinematic viscosity at 40°C.

The approximate viscosity ranges are:

Therefore, ISO VG 68 is more viscous than ISO VG 46.

This difference affects how easily the oil flows through the hydraulic system and how effectively it maintains an oil film under particular operating conditions.

Can You Mix ISO VG 46 and ISO VG 68?

It is generally not recommended to mix different hydraulic oils simply to change viscosity.

Even if both products are mineral-based hydraulic oils, they may have different:

1. Additive packages
2. Base oils
3. Performance levels
4. Compatibility characteristics

If a viscosity change is required, the system should be assessed properly and the appropriate oil-change procedure followed.

How to Choose the Right Hydraulic Oil

Before selecting ISO VG 46 or ISO VG 68, check the following:

1. Manufacturer Recommendation

This should always be your starting point.

2. Operating Temperature

Measure actual fluid temperature rather than relying only on ambient temperature.

3. Hydraulic Pump Type

Different pump designs can have specific viscosity requirements.

4. Operating Pressure

Higher-pressure systems may have different lubrication requirements.

5. Load

Heavy loads can place greater demands on the hydraulic lubricant.

6. Environmental Conditions

Dust, water, humidity, and temperature can influence lubricant selection and maintenance.

7. Hydraulic Oil Specification

Check whether the equipment requires a specific anti-wear or performance specification.

Hydraulic Oil Maintenance Best Practices

Selecting the correct viscosity is only the beginning.

To maintain hydraulic system reliability:

Monitor Oil Condition

Look for changes in color, odor, viscosity, or contamination.

Control Contamination

Keep dust, dirt, and water away from the hydraulic system.

Replace Filters

Use appropriate filters and replace them according to the maintenance schedule.

Check Oil Levels

Maintain the correct reservoir level.

Monitor Temperature

Unexpected increases in hydraulic oil temperature may indicate a system problem.

Perform Oil Analysis

For critical equipment, periodic oil analysis can help identify wear, contamination, oxidation, and other developing problems.

Conclusion

ISO VG 46 and ISO VG 68 hydraulic oils are both valuable lubricant grades, but they serve different viscosity requirements.

ISO VG 46 offers a lower viscosity and generally easier flow, while ISO VG 68 provides higher viscosity and may be suitable for systems requiring a thicker lubricating film or operation at higher temperatures.

The right choice depends on equipment design, operating temperature, load, pump requirements, hydraulic-fluid specifications, and manufacturer recommendations.

For reliable hydraulic performance, never choose oil simply because it is thicker or marketed as heavy-duty.

Choose the viscosity your equipment is designed to use.

With the right DANA hydraulic oil, proper contamination control, regular monitoring, and disciplined maintenance, businesses can support hydraulic system efficiency, component protection, and long-term equipment reliability.

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