Hydraulic oil
By MAXILUB Technical Team · 6 min read · Published · Updated
ISO VG is a viscosity classification
ISO 3448 establishes a viscosity-classification system for industrial liquid lubricants, including hydraulic fluids. The grade number represents the nominal kinematic viscosity at 40 C. It helps buyers compare thickness at the reference temperature, but it does not identify the base oil, additive system, pump performance, seal compatibility or manufacturer approval.
Use the table to interpret a requirement
A manual that calls for ISO VG 46 is asking for a product whose measured viscosity falls within that grade band. The table below is useful for reading a manual or product data sheet; it is not permission to move to the next lighter or heavier grade. Equipment design, start-up temperature and operating temperature determine the required grade.
A cross-reference must match more than the number
Before replacing an existing hydraulic oil, compare the current product and proposed product for viscosity grade, anti-wear or rust-and-oxidation performance, OEM or pump requirements, zinc or ashless formulation, base-oil type and documented compatibility. Similar ISO VG numbers do not prove that two fluids are interchangeable.
Send a complete request to MAXILUB
Include the equipment make and model, exact manual wording, current product, ISO VG, operating environment, monthly volume, package preference and delivery ZIP code. MAXILUB can then review available product documentation and quote an appropriate commercial package without treating the viscosity grade as the entire specification.
Common hydraulic-oil ISO viscosity grades
| ISO grade | Nominal viscosity at 40 C | ISO VG band at 40 C | Buying reminder |
|---|---|---|---|
| ISO VG 32 | 32 mm2/s (cSt) | 28.8-35.2 mm2/s | Common lighter grade; verify start-up and operating limits |
| ISO VG 46 | 46 mm2/s (cSt) | 41.4-50.6 mm2/s | Common mid-range grade; verify pump and manual requirement |
| ISO VG 68 | 68 mm2/s (cSt) | 61.2-74.8 mm2/s | Heavier than 46; do not select from climate alone |
| ISO VG 100 | 100 mm2/s (cSt) | 90-110 mm2/s | Application-specific; confirm the exact equipment requirement |
ISO VG bands are viscosity-classification ranges at 40 C. They do not establish product quality or interchangeability.