AMSOIL guide
ISO Hydraulic Oil Guide
ISO 22, 32, 46, 68, and 100 are the standard viscosity grades for industrial and mobile hydraulic systems, set by the ISO 3448 classification that defines viscosity in centistokes at 40°C. The most common all-around grade is ISO 46, and AMSOIL builds two ISO 46 families: Synthetic Anti-Wear Hydraulic Oil ISO 46 (AWI) for indoor industrial duty, and Synthetic Multi-Viscosity Hydraulic Oil ISO 46 (HVI) for mobile and outdoor equipment with a wide ambient swing. Both ship in quarts, 5-gallon pails, and 55-gallon drums.
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ISO viscosity grades at a glance
Every ISO grade is defined by a target kinematic viscosity at 40°C, plus a tolerance band of plus or minus 10%. The numbers below come straight from the ISO 3448 standard and are what every reputable hydraulic oil supplier ships against.
| ISO grade | Viscosity at 40°C (cSt) | Typical use |
|---|---|---|
| ISO 22 | 19.8 to 24.2 | Cold-climate mobile equipment, snowplow hydraulics, outdoor systems |
| ISO 32 | 28.8 to 35.2 | Indoor industrial machines with low ambient temperature |
| ISO 46 | 41.4 to 50.6 | General-purpose industrial and mobile hydraulics, moderate climates |
| ISO 68 | 61.2 to 74.8 | Hot-climate mobile hydraulics, heavier loads, older vane pumps |
| ISO 100 | 90 to 110 | High-temperature or sustained-load circuits, marine and heavy industrial |
Anti-wear vs R&O hydraulic oil
Hydraulic oils split into two main additive families. Anti-wear (AW, ISO HM) fluids carry zinc-based or ashless EP additives that protect vane, gear, and piston pumps under high pressure. They are the default for modern industrial and mobile hydraulic systems. R&O (rust and oxidation, ISO HL) fluids skip the anti-wear load and focus on corrosion control and oxidation life. They suit low-pressure circulation systems, plain bearings, and some legacy machinery built before AW chemistry was standard.
Substituting R&O for an AW spec leads to accelerated pump wear under load. Substituting AW for R&O is usually safe, but some turbines and compressors are sensitive to zinc additives and call for an ashless AW or a true R&O. Verify the OEM specification before crossing additive families.
Application guide: pick the grade from the equipment
| Equipment / scenario | Recommended grade | Where to buy |
|---|---|---|
| General industrial hydraulics, moderate climate | ISO 46 AW (AWI) | Buy online | Product details |
| Skid steers, excavators, mobile equipment with wide ambient swing | ISO 46 HVI (multi-viscosity) | Buy online | Product details |
| Cold-climate snowplow, snow blower, outdoor power pack | ISO 22 AW or HVI | Buy online | Product details |
| Indoor machine shop press, lift, low ambient | ISO 32 AW | Buy online | Product details |
| Hot-climate skid steer, telehandler, heavier load | ISO 68 HVI | Buy online | Product details |
| Marina, forestry, near-water equipment | ISO 46 biodegradable (HEES) | Buy online | Product details |
Why synthetic anti-wear hydraulic oil pays for itself
Up to 12,000-hour drain interval
Mobile-equipment service life four to six times a conventional AW oil, with oil analysis as the confirmation step.
Wide-temperature pumpability
High viscosity index keeps the fluid in the pump's workable window from cold morning start to hot afternoon load.
Oxidation and varnish control
Synthetic base oil resists the oxidation that turns conventional fluid into the varnish that sticks proportional valves and clogs filters.
Pump-stand validated
AWI passes the Eaton Vickers 35VQ25 vane pump test and Denison HF-0, HF-1, HF-2 piston-pump tests, the same wear screens OEMs use.
Demulsibility and air release
Water and entrained air separate quickly so the pump sees solid fluid instead of foam, which is the single most common cause of cavitation damage.
Bulk-friendly packaging
Quart, 5-gallon pail, and 55-gallon drum sizes scale to garage, shop, and fleet use without changing product code.
How to pick the right ISO grade in three steps
Open the equipment manual.
The OEM lists a specific ISO VG or a viscosity range at operating temperature. That is the authoritative number; do not move one grade up or down without a reason that is in the manual.
Check the cold-start viscosity limit.
Most pump manufacturers publish a maximum Brookfield viscosity at startup. If the equipment cold-soaks below the cold-start limit on the spec'd grade, step down a grade or switch to a multi-viscosity HVI formulation in the same hot-grade number.
Match the additive family.
An AW spec wants an AW oil. A turbine or compressor spec'd for R&O may explicitly forbid zinc-based AW chemistry. Match the additive family, then choose between conventional and synthetic based on operating temperature, duty cycle, and drain-interval target.
AWI vs HVI: anti-wear ISO 46 vs multi-viscosity ISO 46
Both AWI and HVI hit the ISO 46 viscosity grade at 40°C. The difference is what happens away from 40°C. AWI has a viscosity index around 130, which is good for a synthetic AW oil and the right pick for indoor industrial systems that hold a steady operating temperature.
HVI runs a viscosity index closer to 160, so the fluid stays thicker at high operating temperature and thinner at cold startup. That widens the workable range across a 100°F ambient swing without changing grades seasonally. For an excavator that sits overnight at 10°F and sees 110°F afternoon hydraulic-tank temperature in summer, HVI keeps the pump fed without forcing a winter-grade and summer-grade fluid swap.
Bottom line: which ISO hydraulic oil should you use?
- General-purpose industrial hydraulics, moderate climate. Pick AMSOIL Synthetic Anti-Wear Hydraulic Oil ISO 46 (also online from AMSOIL).
- Mobile equipment with wide ambient swing. Pick AMSOIL Synthetic Multi-Viscosity Hydraulic Oil ISO 46.
- Cold-climate snowplow or outdoor power pack. Pick AMSOIL Synthetic Anti-Wear Hydraulic Oil ISO 22.
- Hot-climate, heavier-load mobile hydraulics. Pick AMSOIL Synthetic Multi-Viscosity Hydraulic Oil ISO 68.
- Marina, forestry, near-water equipment. Pick AMSOIL Synthetic Biodegradable Hydraulic Oil ISO 46.
Save on AMSOIL with Preferred Customer pricing
AMSOIL Preferred Customer membership is $20 USD per year ($10 USD for a six-month trial) and unlocks up to 25% off on every product, with free shipping on qualifying orders over $100. Add the membership to the same cart as your order and qualifying products switch to member pricing on that checkout, with no separate sign-up step. See the breakdown on the AMSOIL Preferred Customer page, or sign up directly through the AMSOIL Preferred Customer enrollment page.
ISO hydraulic oil FAQ
What does the ISO number on a hydraulic oil mean?
The ISO viscosity grade (ISO VG) is the fluid's nominal kinematic viscosity in centistokes at 40°C. ISO 22 measures roughly 22 cSt at 40°C, ISO 46 around 46 cSt, ISO 68 around 68 cSt, and ISO 100 around 100 cSt. Higher numbers indicate thicker oil at the reference temperature. The grade is independent of additive chemistry, so two ISO 46 oils still differ in anti-wear, oxidation, and demulsibility.
What is anti-wear hydraulic oil (AW or HM)?
AW stands for anti-wear, and HM is the ISO 6743-4 classification for mineral hydraulic oils with anti-wear additives. Both carry zinc-based or ashless anti-wear chemistry that protects vane, gear, and piston pumps under high pressure. AMSOIL builds the 100% Synthetic Anti-Wear Hydraulic Oil ISO 46 (AWI) for that role, with full pump-stand testing and OEM-grade EP performance.
Anti-wear (AWI) vs multi-viscosity (HVI): which do I pick?
AWI is a straight ISO 46 fluid for stable indoor temperatures and standard industrial duty cycles. HVI (high viscosity index) is built around the same ISO 46 grade with a much higher VI, so it stays in the workable viscosity window across a wider temperature swing. Pick HVI for mobile equipment that cold-soaks overnight and sees hot afternoons, and AWI for indoor industrial machines that hold a tighter operating temperature.
Is ISO 46 the same as SAE 20?
They overlap at 40°C but the two scales are not interchangeable. ISO 46 hydraulic oil sits roughly between SAE 15 and SAE 20 motor oil in 40°C viscosity. The additive packages are completely different. Hydraulic oil is tuned for anti-wear, demulsibility, air release, and filterability; motor oil carries detergents and dispersants the hydraulic circuit does not want. Do not substitute motor oil for hydraulic oil in regular service.
Can I mix ISO 32 and ISO 46 hydraulic oil?
Short-term, yes, if both fluids share the same anti-wear chemistry (zinc-based AW with zinc-based AW, or ashless with ashless). The blend lands between the two grades. Long-term, drain and refill with a single ISO grade matched to the pump's specification so the viscosity at operating temperature stays in the pump manufacturer's window.
How often should hydraulic oil be changed?
Conventional anti-wear hydraulic oil is typically changed every 2,000 operating hours in moderate-duty systems, with shorter intervals for high-temperature or contaminated service. AMSOIL Synthetic Anti-Wear Hydraulic Oil is rated for up to 12,000 hours in mobile equipment and up to 2x OEM in industrial systems. Pair the extended drain with periodic oil analysis to confirm wear metals, water, and TAN stay in bounds.
Does AMSOIL hydraulic oil come in 5-gallon pails and drums?
Yes. AMSOIL Synthetic Anti-Wear Hydraulic Oil and Synthetic Multi-Viscosity Hydraulic Oil ship in quarts, 5-gallon pails, and 55-gallon drums in every common ISO grade. Bulk pricing scales with the larger package sizes, and Preferred Customer membership stacks up to 25% off the same package.
Where do I buy AMSOIL hydraulic oil?
Order online from AMSOIL on the hydraulic oil page, which lists every ISO grade in both AW and multi-viscosity formulations. The matching hydraulic oil overview on Synthetic Oil Distributor covers the same lineup with side-by-side spec comparisons.
Order AMSOIL hydraulic oil
Order online from AMSOIL's Synthetic Anti-Wear Hydraulic Oil ISO 46 product page. To unlock up to 25% off, add an AMSOIL Preferred Customer membership to the same cart and qualifying products switch to member pricing immediately, with no separate sign-up step.