Which Hydraulic Oil Is Better - Aw 46 Or Aw 68 ?

By Author: bdean
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Choosing the right hydraulic oil is essential for maintaining equipment performance, reducing wear, and extending machinery life. Among the most commonly used hydraulic oil grades are AW 46 and AW 68. Both are formulated with anti-wear additives to protect hydraulic components, but they differ in viscosity and suitability for particular operating conditions.
If you are unsure whether AW 46 or AW 68 is better for your machinery, understanding their differences can help you make an informed decision. This guide explains their properties, applications, benefits, and selection criteria.
What Is AW 46 Hydraulic Oil?
AW 46 hydraulic oil is an anti-wear hydraulic fluid with a nominal kinematic viscosity of approximately 46 centistokes (cSt) at 40°C. It is designed to lubricate hydraulic pumps, valves, cylinders, and other components while helping reduce friction and wear.
Its relatively lower viscosity compared with AW 68 allows it to flow more easily under suitable operating conditions. This makes it a common choice for industrial hydraulic systems, mobile equipment, and machinery operating within the temperature ...
... and viscosity limits specified by the manufacturer.
Key benefits of AW 46 include:
• Good flow characteristics in compatible hydraulic systems.
• Anti-wear protection for pumps and other moving components.
• Support for efficient hydraulic operation when the correct viscosity is maintained.
• Suitability for a wide range of industrial and mobile applications.
AW 46 is often selected for equipment operating in moderate temperature conditions, provided it meets the manufacturer's specifications.
What Is AW 68 Hydraulic Oil?
AW 68 hydraulic oil has a nominal kinematic viscosity of approximately 68 cSt at 40°C. It is thicker than AW 46 at the same reference temperature and is formulated to provide lubrication and anti-wear protection in compatible hydraulic systems.
The higher viscosity may help maintain an adequate lubricating film under certain operating conditions. However, the oil must still meet the equipment manufacturer's viscosity and performance requirements.
Key benefits of AW 68 include:
• Higher viscosity than AW 46 at 40°C.
• Anti-wear protection for compatible hydraulic components.
• Suitability for hydraulic systems designed for thicker fluids.
• Potentially appropriate performance in warmer operating environments, depending on the equipment and oil formulation.
AW 68 is commonly considered for industrial machinery and hydraulic systems that require a higher-viscosity fluid. It should not be selected solely because the equipment operates in a warm environment.
AW 46 vs AW 68 Hydraulic Oil: Key Differences
The primary difference between AW 46 and AW 68 is viscosity. Both grades can provide anti-wear protection, but their flow and lubrication characteristics differ.
Feature AW 46 AW 68
Nominal viscosity at 40°C 46 cSt 68 cSt
Relative thickness Lower Higher
Flow characteristics Flows more easily at the same temperature More resistant to flow at the same temperature
Typical selection Systems specifying ISO VG 46 Systems specifying ISO VG 68
Common applications Compatible industrial and mobile hydraulic systems Compatible industrial hydraulic systems requiring higher viscosity
Cold-start behaviour Generally easier to pump at the same temperature May require more effort to pump at the same temperature
Actual performance depends on the oil formulation, temperature, hydraulic system design, and operating conditions.
Which Hydraulic Oil Is Better: AW 46 or AW 68?
Neither grade is universally better. The correct choice depends on the machinery manufacturer's recommendations, operating temperature, system design, and required viscosity.
Choose AW 46 When:
• The equipment manufacturer specifies ISO VG 46 hydraulic oil.
• The system requires a lower-viscosity fluid.
• Easier fluid circulation is important under the intended operating conditions.
• Your machinery operates within the recommended temperature range for AW 46.
Choose AW 68 When:
• The manufacturer specifies ISO VG 68 hydraulic oil.
• The hydraulic system requires a higher-viscosity fluid.
• Operating conditions and system clearances are compatible with the thicker oil.
• The equipment is designed to maintain adequate flow and lubrication with AW 68.
Important: Using an oil that is too thick can increase resistance to flow, particularly during cold starts. Oil that is too thin may not provide the required lubricating film. Always check the equipment manual before changing grades.
Can AW 46 or AW 68 Be Used in Cars and Diesel Engines?
Hydraulic oil is designed for hydraulic systems, not automatically for every automotive application.
Engine oil lubricates internal engine components and is formulated to meet specific engine performance requirements. Diesel engines, in particular, require oil that meets the manufacturer's viscosity and performance specifications.
Similarly, cars may use different fluids for their engines, transmissions, power steering systems, brakes, and other components. These fluids are not necessarily interchangeable.
AW 46 or AW 68 should only be used in a vehicle system if the manufacturer explicitly approves the relevant fluid specification. Do not substitute hydraulic oil for engine oil, diesel engine lubricant, brake fluid, or transmission fluid simply because their viscosities appear similar.
Tips for Selecting the Right Hydraulic Oil
Consider these practical steps before purchasing hydraulic oil:
1. Check the equipment manual: Confirm the recommended ISO viscosity grade and required performance standards.
2. Consider operating temperatures: Oil viscosity changes with temperature, affecting flow and lubrication.
3. Review additive requirements: Ensure the fluid provides the anti-wear and other performance properties required by the system.
4. Avoid unnecessary grade changes: Switching between AW 46 and AW 68 without checking compatibility can affect equipment performance.
5. Follow maintenance intervals: Inspect oil condition, monitor contamination, and replace the fluid according to manufacturer guidance.
Selecting a suitable hydraulic oil can help improve reliability, reduce unnecessary wear, and support consistent machinery performance.
Conclusion
AW 46 and AW 68 hydraulic oils both provide anti-wear protection, but they serve systems with different viscosity requirements. AW 46 is the lower-viscosity option, while AW 68 is thicker at the same reference temperature.
The best choice is the grade specified by your equipment manufacturer, not simply the thicker or more expensive oil. Correct selection, regular maintenance, and adherence to operating recommendations can help protect hydraulic components and extend equipment service life.

Frequently Asked Questions (FAQs)
1. What is the main difference between AW 46 and AW 68 hydraulic oil?
The main difference is viscosity. AW 46 has a nominal viscosity of 46 cSt at 40°C, while AW 68 has a nominal viscosity of 68 cSt at the same temperature.
2. Is AW 68 better than AW 46?
Not necessarily. AW 68 is better only when the equipment requires its higher viscosity. AW 46 may be more suitable for systems designed for the lower-viscosity grade.
3. Can I replace AW 46 with AW 68?
Only if the equipment manufacturer permits the change. Using a higher-viscosity oil than recommended can affect flow, energy consumption, and system performance.
4. Can AW 46 hydraulic oil be used as engine oil?
No, not unless a specific product is explicitly approved for that engine application. Hydraulic oil and engine oil have different performance requirements.
5. Which hydraulic oil is suitable for hot weather?
AW 68 may be appropriate for certain systems operating at higher temperatures, but ambient temperature alone is not enough to determine the correct grade. Follow the manufacturer's recommendations.
6. What does AW mean in hydraulic oil?
AW stands for anti-wear. It indicates that the hydraulic fluid contains additives designed to help protect components against wear.
7. How often should hydraulic oil be changed?
The replacement interval depends on the equipment manufacturer's instructions, operating conditions, oil analysis, and contamination levels. Follow the recommended maintenance schedule rather than relying on a universal interval.