Short answer: "AW" means anti-wear hydraulic oil — a fluid with anti-wear additives (typically ZDDP) plus rust and oxidation inhibitors that protect pumps and valves under pressure. The number — ISO 32, 46, or 68 — is the ISO viscosity grade, the oil's kinematic viscosity at 40 °C. Lower number = thinner oil (ISO 32), higher number = thicker (ISO 68). Pick the grade based on your pump type, operating temperature, and the equipment maker's specification, not by preference.
What "AW" means
Anti-wear (AW) hydraulic oils add an anti-wear additive package — most commonly zinc dialkyldithiophosphate (ZDDP) — to a refined base oil, along with rust and oxidation inhibitors and anti-foam agents. This protects high-pressure vane and piston pumps from metal-to-metal wear. Plain R&O (rust & oxidation) oils lack this AW protection and are used in lighter, lower-pressure systems.
What the ISO number means
ISO Viscosity Grade (ISO VG) is the oil's kinematic viscosity at 40 °C, in centistokes (cSt):
- ISO 32 ≈ 32 cSt @ 40 °C — thinner
- ISO 46 ≈ 46 cSt @ 40 °C — mid-range
- ISO 68 ≈ 68 cSt @ 40 °C — thicker
The grade is about viscosity only; all three can be AW oils.
Where each grade is used
- AW ISO 32: lighter, lower-viscosity systems; cold-climate or cooler operating temperatures; higher-speed systems; many mobile machines in cold weather.
- AW ISO 46: the most common general-purpose industrial and mobile hydraulic grade — a balanced choice for moderate temperatures and typical pressures.
- AW ISO 68: higher operating temperatures and pressures, warmer climates, heavier-duty or older systems that benefit from a thicker film.
How to choose
- Follow the OEM spec first — the machine builder specifies an AW grade and often a standard (e.g., DIN 51524-2 HLP, ISO 11158 HM, Denison, Eaton/Vickers).
- Match operating temperature — colder ambient/lighter loads favor ISO 32; hotter/higher-pressure favor ISO 68; ISO 46 is the common middle.
- Match pump type — vane and piston pumps need genuine AW protection.
- Don't switch grades arbitrarily — viscosity affects efficiency, film strength, and component life.
Ultra1Plus hydraulic oils
Ultra1Plus supplies anti-wear hydraulic oils, Made in USA, from retail through bulk drum and tote formats:
- Hydraulic oil & HTF: Shop hydraulic oil & HTF
- Hydraulic fluids (off-highway): Shop hydraulic fluids
Need a specific AW ISO grade or a bulk drum/tote? Check the spec on the product page or request bulk pricing.
Frequently asked questions
What is AW ISO 68 hydraulic oil used for?
AW ISO 68 is an anti-wear hydraulic oil with an ISO viscosity grade of about 68 cSt at 40 °C. It's used in hydraulic systems running at higher temperatures and pressures, in warmer climates, and in heavier-duty or older equipment that benefits from a thicker oil film. Always match the equipment maker's specification.
What does "AW" mean in hydraulic oil?
AW stands for anti-wear. These oils contain anti-wear additives (typically ZDDP) plus rust and oxidation inhibitors to protect vane and piston pumps under pressure.
What is the difference between AW 32, AW 46, and AW 68?
The number is the ISO viscosity grade at 40 °C: ISO 32 is the thinnest, ISO 46 is mid-range and most common, and ISO 68 is the thickest. All are anti-wear hydraulic oils; choose the grade by temperature, pressure, pump type, and OEM spec.
Can I use ISO 46 instead of ISO 32 or 68?
Only if the equipment specification allows it. Viscosity affects efficiency, film strength, and component life, so follow the OEM-recommended grade rather than substituting.
Is AW hydraulic oil the same as R&O oil?
No. R&O oils have rust and oxidation protection but lack the anti-wear additives that AW oils use to protect high-pressure pumps.