Lubricant guide ·
Which hydraulic oil grade? ISO VG 32 vs 46 vs 68
What the ISO VG number means, how the machine, the pump and Rajkot's heat decide the grade, and why a mechanical power press is a different case.
Walk into almost any unit in Shapar-Veraval or Metoda GIDC and the hydraulic power packs, presses and moulding machines will be running on one of three grades: ISO VG 32, 46 or 68. The numbers look close, but the wrong one shows up quickly. You get a sluggish machine on a cold morning, a pump that runs hot by afternoon, or seals and pumps that wear out early. Here is how to choose.
What the ISO VG number means
ISO VG stands for viscosity grade, under the ISO 3448 standard. The number is the oil's kinematic viscosity in centistokes (cSt) at 40°C, within ±10%. An ISO VG 46 oil therefore measures between about 41.4 and 50.6 cSt at 40°C. A higher number means a thicker oil: VG 68 is roughly half as thick again as VG 46 at the same temperature, and VG 32 is about 30% thinner.
Viscosity is not a measure of quality. A VG 32 oil is not "lighter duty" than a VG 68. It is simply suited to a different machine and a different operating temperature.
Start with the machine maker's specification
The right grade is the one the machine builder specifies, on the nameplate, in the manual or on the label of the power pack's tank. The hydraulic pump has an allowed viscosity range at start-up and at running temperature, and the builder has chosen a grade that keeps the pump inside it. If the manual also lists a specification such as DIN 51524 Part 2 (HLP), match that as well as the grade.
If the manual is lost, the oil already in the machine is the next-best guide, as long as the machine has been running well on it. Send us the machine make and model, or a photo of the tank label, and we can help check.
Where each grade is usually used
| Grade | Typical use |
|---|---|
| ISO VG 32 | Precision machine tools, CNC machine hydraulics, systems with servo or proportional valves, and systems that run cool or at lower pressures. |
| ISO VG 46 | The common general-purpose grade: power packs, hydraulic presses and injection moulding machines at normal operating temperatures. |
| ISO VG 68 | Heavy presses, high loads, systems that run hot, and older pumps with some wear, where the machine builder allows the heavier grade. |
Rajkot's heat and your oil temperature
Oil thins as it warms. A system that is comfortable on VG 46 in winter can run noticeably hotter in May, especially in a closed shed with the power pack beside a furnace or a moulding machine. That is one reason VG 68 is common in heavy presses in hot climates.
Before moving up a grade, though, find out why the oil is hot. A blocked or undersized cooler, a relief valve that is bypassing or a low tank level will overheat any grade. As a rule of thumb, most industrial hydraulic systems are happiest with the tank oil at roughly 40–60°C. Oil that regularly runs much hotter oxidises faster, darkens, and leaves sludge and varnish that make valves stick.
Mechanical power presses are a different case
A mechanical power press, the flywheel-and-crank type common in sheet-metal and pressing units, mostly needs gear oil for its gears and grease or oil for its bearings and slides, not hydraulic oil. Many do have a small hydraulic circuit for overload protection or for the clutch and brake, and that circuit takes whatever hydraulic oil the press maker specifies. A hydraulic press, by contrast, runs entirely on hydraulic oil. Check which kind you have before you order.
Anti-wear (HLP) or plain (HL)?
Most industrial systems need an anti-wear hydraulic oil, usually labelled HLP or AW, to DIN 51524 Part 2. The anti-wear additive protects vane and gear pumps under high pressure. Plain HL oils have no anti-wear additive and are meant for lightly loaded systems where the maker allows them. If in doubt, an anti-wear oil is the safer choice, but the specification still comes first.
Switching grade or brand
Don't top up a VG 46 system with VG 68, and don't mix brands casually. Additive packages differ, and mixing can cause foaming, blocked filters or sludge. If you are changing grade or brand, drain the old oil, flush the system if it is dirty, change the filters and refill with the new oil. Keep top-up containers clean and closed, because dirt that gets into the tank ends up in the pump and valves.
Buying hydraulic oil in Shapar-Veraval and Metoda GIDC
We stock anti-wear hydraulic oils in ISO VG 32, 46 and 68 from several brands at our shop at Tilara Gate, near the Shapar Veraval Industrial Association. Regular customers in Shapar-Veraval get same-day delivery (a minimum order applies). We also deliver to units in Metoda GIDC, also known as GIDC Lodhika, and across Rajkot, with timing confirmed per order. Every order comes with a GST bill, and factories get a bulk discount. See the hydraulic oils we stock, or read about hydraulic oil supply in Metoda GIDC.
