AW68 hydraulic fluid is a high-viscosity lubricant engineered for heavy industrial and mobile hydraulic systems operating under high pressure and elevated temperatures.
AW68 hydraulic fluid is an ISO Viscosity Grade 68 lubricant built for the toughest jobs in industrial and mobile hydraulics. Understanding what is AW68 hydraulic fluid used for starts with its viscosity — it’s thicker than standard hydraulic oils, making it ideal for heavy loads, high heat, and systems prone to leakage under load. This fluid powers equipment that pushes, lifts, and digs under extreme conditions, and its formulation is designed to protect gear, vane, and piston pumps from wear.
What Is AW68 And What Makes It Different?
AW68 belongs to the ISO Viscosity Grade system, where the number 68 indicates a kinematic viscosity of roughly 68 mm²/s at 40°C. That puts it between thinner grades like ISO 32 and 46 and heavier gear oils — roughly equivalent to an SAE 20 weight lubricant. The higher viscosity means it maintains a load-bearing film under high pressure where lighter oils would squeeze out and cause metal-on-metal contact.
Most AW68 fluids contain zinc anti-wear additives that reduce pump wear and extend equipment life. They also meet a range of industry standards including ASTM D6158 HM, ISO 11158, DIN 51524 (HLP), Parker Hannifin HF-0/HF-2, and Cincinnati P-68/P-69/P-70. Major brands like ExxonMobil manufacture their own certified versions—Mobil Hydraulic AW 68 meets Denison HF-0 and HF-2 requirements, confirming its suitability for high-pressure pump systems.
| Property | Value | Test Method |
|---|---|---|
| Viscosity @ 40°C | 68 mm²/s | ASTM D445 |
| Viscosity @ 100°C | 8.2–8.97 mm²/s | ASTM D445 |
| Viscosity Index | 95–105 | ASTM D2270 |
| Pour Point | -18°C to -27°C | ASTM D97 |
| Flash Point | 226°C–241°C | ASTM D92 |
| Density @ 15°C | 0.88 kg/L | ASTM D4052 |
| Dielectric Strength | >35 kV | — |
| Additive Type | Zinc anti-wear | — |
Where AW68 Is Used: Equipment, Pumps, And Operating Conditions
AW68 is the standard choice for heavy hydraulic systems that run under continuous high pressure. You’ll find it in bulldozers, cranes, hydraulic presses in the 10-to-40 ton range, excavators, and agricultural machinery like tractors and harvesters. It handles gear pumps, vane pumps, radial piston pumps, and axial piston pumps — the full range of designs found in mobile and industrial equipment.
The fluid excels in high-temperature environments where thinner oils would thin out and leak past seals. It also tolerates minor water contamination and dirt better than lower-viscosity alternatives, making it a practical pick for construction sites and farming operations where conditions aren’t perfectly clean. For a direct comparison of top-rated AW68 hydraulic fluid products, our roundup covers the leading options available in the US market. Its dielectric strength above 35 kV also makes it safe to use in equipment near electrical components.
What Are The Key Limitations Of AW68?
AW68 is a specialized fluid that works best within its design range. Here are the main constraints to keep in mind:
- Cold-weather performance. With a pour point between -18°C and -27°C, the fluid thickens significantly at freezing temperatures. Equipment run in cold climates needs a warm-up period to avoid pump starvation.
- Wrong applications. Using AW68 in light-duty machinery — small presses under 5 tons, CNC equipment, or log splitters — reduces efficiency and can cause sluggish operation. Those systems typically need ISO 32 or 46.
- Water contamination limits. While AW68 handles minor water better than some oils, excessive water still causes foaming. Systems with heavy water ingress may need a specialized fluid rated for wet environments.
- Zinc compatibility. Standard AW68 contains zinc anti-wear additives. Some modern servo-valves and specific seal materials require non-zinc (HF-0) fluids. Check OEM specs before mixing.
- Drain interval. Basic AW68 grades typically require changes every 2,000 operating hours. High-performance variants can stretch that, but the standard fluid needs regular replacement.
FAQs
Can I run AW68 in sub-zero temperatures?
Not without precautions. Below -18°C the fluid becomes very thick and may not flow into pumps, risking cavitation and damage. If cold operation is unavoidable, use an ISO 32 grade or install a fluid heater to warm the system before startup.
What happens if I mix AW68 with ISO 46 in the same system?
Mixing viscosity grades dilutes the oil’s properties. The resulting blend will have a viscosity somewhere between 46 and 68, which may not provide adequate film strength for high-load pumps or may be too thick for cold starts. The safest move is to drain and refill with one grade confirmed by the equipment manufacturer.
Is AW68 the right fluid for a log splitter or small press?
Usually not. Most log splitters and small shop presses specify ISO 32 or 46 because their pumps are smaller and run at lower pressures. AW68 will make them sluggish, increase heat, and reduce cycle speed. Check the equipment manual — the correct grade is almost always listed.
References & Sources
- ExxonMobil. “Mobil Hydraulic AW 68 Technical Data Sheet.” Confirms viscosity specs, additive type, and Denison HF-0/HF-2 compliance.
- Lott Oil. “Standard Hydraulic Oil AW68 Product Data.” Provides pour point, flash point, and drain interval figures.