Hydraulic Oil

Hydraulic Oil — ISO VG 32, 46 and 68 for Industrial and Mobile Equipment

Hydraulic oil does far more than transmit power in a hydraulic system — it lubricates pump components, cylinders, valves and motors; carries heat away from high-work-rate components; prevents corrosion on internal metal surfaces; and maintains a stable film between moving parts to minimise wear. Selecting the right hydraulic oil viscosity grade and additive package for the operating conditions is fundamental to system efficiency, pump life and overall reliability. AIMS supplies hydraulic oil grades stocked for fast Australia-wide dispatch.

Viscosity Grades — Which to Choose

• ISO VG 46 — the most common viscosity grade used in industrial hydraulic systems operating at typical ambient temperatures (15–35°C). The default choice for most stationary plant.
• ISO VG 32 — specified for systems operating in cold conditions or at high speeds where lower viscosity improves cold-start performance and energy efficiency.
• ISO VG 68 — for high-temperature environments, heavily loaded systems, or applications where higher viscosity is needed to maintain adequate oil film thickness at operating temperature.

Always check the equipment manufacturer's specification — using an incorrect viscosity grade affects system efficiency and can cause excessive wear or inadequate lubrication. For ISO VG ↔ SAE ↔ AGMA cross-reference and the full viscosity-vs-temperature relationship, see the Oil Viscosity Chart.

Anti-Wear (AW / HM / HV) Hydraulic Oils

Premium anti-wear hydraulic oils (designated AW or HM to ISO 11158) contain zinc-based (ZDDP) or zinc-free anti-wear additive packages that protect pump components under high-load and high-pressure conditions. AW hydraulic oils are the standard specification for industrial hydraulic systems with vane, piston and gear pumps. HV (high viscosity index) oils are specified where wider operating temperature ranges are expected. Zinc-free anti-wear hydraulic oils are available for systems with servo valves and other sensitive components where zinc-based additives may cause deposits or valve sticking.

For the full breakdown of hydraulic oil categories (HL, HM, HV, HEPG, HEES, HFC, HFD), pump compatibility and how to read a hydraulic oil specification sheet, see the Hydraulic Oil Guide covering ISO VG grades, AW vs HV and compatibility with seals and paints.

Fire-Resistant & Biodegradable Grades

Fire-resistant hydraulic fluids are required where hot surfaces, open flames or molten metal are present — steel mills, die casting machines, foundries and underground coal mines. Water-glycol (HFC), water-in-oil emulsion (HFB) and phosphate ester (HFD) fluids have different handling and compatibility requirements from mineral oil. Always verify seal, hose, paint and reservoir compatibility before converting a system from mineral oil to a fire-resistant fluid — many seal materials swell or harden in HFD service.

Biodegradable hydraulic oils based on synthetic esters (HEES) or vegetable oils (HEPG) are specified for forestry, marine, agriculture and other environmentally sensitive applications where spills could cause environmental contamination.

Common Failure Causes & How Oil Choice Helps

• Pump wear: wrong viscosity at operating temperature, or oxidised oil losing anti-wear additives.
• Valve sticking: contamination, varnish from oil oxidation, or chemical incompatibility (zinc-based additives in servo-valve systems).
• Cylinder seal failure: high temperatures, the wrong fluid type for the seal material, or particulate contamination scoring rod surfaces.
• Foaming and aeration: water contamination, air entry through return-line, or wrong oil for the operating temperature.

Routine oil sampling and condition monitoring catches these before component damage occurs.

Related Lubricants & Equipment

• Lubrication — the full AIMS range of lubricants including grease, gear oil, chain oil, slideway oil and machine cutting fluid.
• Gear Oil Guide — for gearbox lubrication selection (EP ratings, GL-4 vs GL-5, viscosity).
• Industrial Lubricants Guide — full overview of industrial lubricant types and how to choose.
• Hydraulics — hydraulic components, hoses and fittings.
• Oil Seals & O-Rings — shaft and cylinder seals.

Order Hydraulic Oil from AIMS Industrial

AIMS Industrial supplies hydraulic oil in standard pail, drum and IBC quantities for industrial and commercial customers. Technical data sheets and safety data sheets are available for all stocked grades. For volume pricing, specific OEM-grade requirements or technical questions, contact our team — we ship Australia-wide from our Sydney warehouse.

People Also Ask — Hydraulic Oil

Q: What hydraulic oils does AIMS stock?

ISO VG 32, VG 46, VG 68, and VG 100 hydraulic oils — the workshop standards for most hydraulic equipment. Specialty hydraulic fluids: zinc-free for environmentally-sensitive applications, biodegradable for forestry and water-contact equipment, fire-resistant HFC/HFD for high-temperature environments, food-grade NSF H1 for food processing. Brand mix includes Anglomoil, Castrol, Penrite, and dedicated hydraulic oil specialists. Match grade to equipment manufacturer's spec — wrong oil grade reduces equipment life. See [Hydraulic Oil Guide](/blogs/product-guides/hydraulic-oil-guide).

Q: ISO VG 32, 46, or 68 — which?

ISO VG 32 (lower viscosity): cold-climate operation, light-duty systems, fast-acting hydraulic systems. ISO VG 46 (medium viscosity): most workshop and industrial hydraulics — the workshop standard. ISO VG 68 (higher viscosity): hot-climate operation, heavy-duty systems, slower-acting hydraulics. ISO VG 100: very heavy industrial, mining equipment, high-temperature operation. Match to manufacturer spec on the equipment nameplate or service manual. Don't switch without engineering review.

Q: AW (anti-wear) hydraulic oil — what does it mean?

AW (Anti-Wear) hydraulic oil: contains zinc-based ZDDP (zinc dialkyldithiophosphate) additives that protect against wear under boundary lubrication conditions. Workshop standard for most hydraulic systems. R&O (Rust and Oxidation) hydraulic oil: simpler additive package without anti-wear additives. Used in light-duty systems and applications where zinc-based additives can't be tolerated. For most workshop hydraulics: AW oil. For specialty applications (food machinery, environmentally-sensitive): zinc-free or specialty fluids.

Q: How often do I change hydraulic oil?

Depends on equipment, duty cycle, and contamination. Workshop hydraulics with moderate use: every 1-2 years OR 2000 operating hours, whichever comes first. Heavy industrial hydraulics: 1000-2000 hours or annual. Mining and continuous duty: dedicated oil analysis programs (sample testing every 250-500 hours). Visible signs requiring change: dark colour, water contamination (cloudy), unusual smell, debris in oil. Change full system (drain, flush, refill) rather than just topping up — old oil dilutes new oil's additive package.

Q: Can I mix hydraulic oil brands?

Same grade and additive type: generally yes — mixing AW VG 46 from different brands is usually OK. Mixing different additive packages (AW with zinc-free, or HFD with mineral oil): NO — incompatible additives can form sludge and damage seals. When in doubt, drain and replace rather than mix. For workshop with multiple hydraulic equipment, standardising on one brand and grade simplifies inventory and reduces mixing errors. Document the oil used in each system.