LUBRICATION GUIDE
Hydraulic Oil Grades Explained: Viscosity and Type
By the PCG Technical Desk · Updated 27 September 2026
Quick answer: A hydraulic oil is described by two things. The first is its viscosity grade (ISO VG 32, 46, 68…). The second is its type: the additive performance class, such as R&O (HL), anti-wear (HM / DIN HLP) or high-VI anti-wear (HV / DIN HVLP). You need both to pick the right oil.
Types under ISO 6743-4 and DIN 51524
| ISO 6743-4 | DIN 51524 | What it is | SERVO examples (IOCL) |
|---|---|---|---|
| HL | Part 1 (HL) | Rust & oxidation inhibited, no anti-wear | Servocirol (DIN 51524 H / HL) |
| HM | Part 2 (HLP) | HL + anti-wear additives | Servosystem HLP; Servosystem (anti-wear, IS 10522) |
| HV | Part 3 (HVLP) | HM + high viscosity index for wide temperatures | Servosystem HVLP (DIN 51524 Part 3), Servohydrex |
| HFA / HFC / HFD | — | Fire-resistant fluids | Servoaquol, Servofyress WG / HFDU / HFDR |
| HEES etc. | — | Environmentally acceptable | Servosystem BD / BD S |
Which type do most machines need?
Modern industrial pumps under pressure need anti-wear (HM/HLP) oil. R&O oils suit lightly loaded circulation systems and some turbine-quality applications. HV oils help mobile and outdoor equipment that starts cold and runs hot. Fire-resistant fluids are needed near hot metal and in mines.
See the full SERVO hydraulic oil range, or read 46 vs 68 for viscosity choice.
Outside Karnataka? The technical information on this page applies anywhere in India. PCG Business Solutions supplies SERVO in seven Karnataka districts. If you are in another state, send us your requirement and we will point you to IndianOil's authorised channel for your area, or answer any technical question about the grade.
