AW32 vs AW46 vs AW68 Hydraulic Oil (ISO VG): How to Choose?
Industrial lubricants - hydraulic oil AW32, AW46, AW68
When selecting hydraulic oil, you’ll often come across three common anti-wear grades: AW32, AW46, and AW68. But what do these numbers mean, and how do you choose the best option for your machinery? Is a higher number always the better choice? This guide explains the key differences between these essential grades, walks you through the right selection process, and highlights the critical risks of using the wrong viscosity.
The main difference between AW32, AW46, and AW68 hydraulic oils lies in their viscosity—a measure of how thick or thin the fluid is at a specific temperature. In general, the higher the number, the higher the viscosity. Thicker oils (like AW68) are better suited for higher operating temperatures or heavier-duty systems, while thinner oils (like AW32) perform better in colder environments or lighter applications.
What Does “AW” Stand For? “AW” stands for Anti-Wear
This means the hydraulic oil contains specialized additives designed to reduce metal-to-metal wear in high-pressure hydraulic systems.
AW oils are the industry standard, widely used across demanding applications such as:
■ CNC machinery
■ Automation equipment
■ Hydraulic presses
■ Heavy industrial systems requiring reliable performance under sustained load.
Hydraulic Oil Grades & Applications
These hydraulic oil grades correspond directly to the ISO VG (International Standards Organization Viscosity Grade) classification system. Each number reflects the oil’s kinematic viscosity, measured in centistokes (cSt) at 40°C, which is a critical factor in hydraulic fluid performance and system efficiency.
| Model | ISO VG | Viscosity at 40°C (cSt) | Temperature Range | Common Applications |
|---|---|---|---|---|
| WILL AW-32 | ISO VG 32 | ~32 cSt | Low-temp (<20°C) | High-speed systems, indoor compressors, automation lines |
| WILL AW-46 | ISO VG 46 | ~46 cSt | Normal (20–35°C) | CNC lathes, injection molding machines, handling equipment |
| WILL AW-68 | ISO VG 68 | ~68 cSt | High-temp (>35°C) | Outdoor machines, hydraulic lifts, presses |
How to Choose the Right Grade
Selecting the optimal hydraulic oil grade isn't about choosing the highest viscosity, it's about matching the fluid precisely to your operating conditions and equipment specifications. Consider these three critical factors:
1. Operating Temperature (Viscosity Index)
■ Low Temperatures / Cold Startups (< 20°C): Requires lower viscosity (e.g., AW32) to ensure fluid flows effortlessly, preventing pump cavitation and cold-start resistance.
■ Standard Ambient / Indoor Operation (20°C–35°C): The industry baseline (e.g., AW46) offers balanced fluidity and protection under normal factory conditions.
■ High Heat / Continuous Outdoor Use (> 35°C): Demands higher viscosity (e.g., AW68) to maintain a sufficient lubricating film and avoid thermal breakdown.
2. System Pressure & Operating Speed (Mechanical Load)
■ High-Speed, Low-Pressure Systems: Lower viscosity fluids reduce internal fluid friction, lower energy consumption, and minimize heat accumulation.
■ Heavy-Duty, High-Pressure Systems: Higher viscosity fluids provide superior film strength, protecting pumps, valves, and actuators from severe metal-to-metal wear.
3. Equipment Manufacturer Guidelines
■ Strict Tolerances: Modern high-precision CNC machinery and automated lines specify an exact ISO VG range in their manuals.
■ Warranty Protection: Using fluids outside OEM specifications risks reduced operational efficiency, component damage, and potential warranty voidance.
Critical Risks of Using the Wrong Hydraulic Oil
Using the wrong hydraulic oil viscosity can have a significant negative impact on your system’s performance and longevity. If the oil is too thin, it may result in low system pressure and insufficient lubrication. On the other hand, oil that’s too thick can cause the system to overheat, respond sluggishly, and work harder than necessary—leading to increased wear and tear on critical components over time. To avoid these issues, it’s essential to consult your equipment manufacturer's specifications and use a reliable hydraulic oil viscosity chart when selecting the appropriate ISO VG grade for your application.
Final Tip: Always Choose Based on Application
Viscosity isn’t one-size-fits-all. Choosing the right AW hydraulic oil protects your equipment, maximizes efficiency, and reduces maintenance costs. When in doubt:
✅ Check your equipment manual
✅ Review environmental conditions
✅ Use an accurate viscosity chart
Export Documents & Compliance Support
HLJH can support export-related documentation based on product series, destination country, and order requirements. Available documentation may include Certificate of Origin (COO), REACH Declaration, RoHS Declaration, SDS, TDS, and other product-related documents when applicable. Certificate of Analysis (COA) may be provided upon customer request, depending on product series, batch requirements, and order conditions. Please indicate your required documents when submitting an inquiry.
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Last Updated: 2026-07-28
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