HM and HV hydraulic oils are not different viscosity grades. They are different hydraulic oil performance categories defined by ISO standards.
The key difference between HM and HV hydraulic oil is viscosity index. HM oils have standard viscosity index, while HV oils have a higher viscosity index and maintain viscosity more consistently as temperature changes.
This page explains what HM and HV hydraulic oil actually mean, how they differ in practice, and how to select the correct type based on operating conditions rather than assumptions.
What HM hydraulic oil means
HM is an ISO 11158 hydraulic oil classification for mineral-based anti-wear hydraulic oils with standard viscosity index.
HM hydraulic oils are formulated to provide:
- Anti-wear protection
- Oxidation stability
- Rust and corrosion protection
- Reliable performance at stable operating temperatures
HM oils are the most commonly specified hydraulic oils for industrial and mobile hydraulic systems operating within a relatively narrow temperature range.
What HV hydraulic oil means
HV is an ISO 11158 hydraulic oil classification for hydraulic oils with a higher viscosity index.
HV hydraulic oils contain viscosity index improvers that reduce the rate at which viscosity changes with temperature.
This allows HV oils to:
- Remain fluid during cold start
- Maintain sufficient film thickness at elevated operating temperature
- Operate effectively across wider temperature ranges
The key difference between HM and HV hydraulic oil
The difference between HM and HV hydraulic oil is not wear protection. Both are anti-wear hydraulic oils.
The difference is viscosity stability with temperature.
| Feature | HM hydraulic oil | HV hydraulic oil |
|---|---|---|
| Viscosity index | Standard | High |
| Temperature range | Narrow to moderate | Wide |
| Cold start behaviour | Acceptable within limits | Improved flow |
| High temperature film strength | Depends on viscosity grade | Better retention at temperature |
When HM hydraulic oil is the correct choice
HM hydraulic oil is typically suitable where:
- Operating oil temperature is stable
- Seasonal temperature variation is limited
- The manufacturer specifies HM or equivalent standards
- Cold start conditions are not severe
In many industrial applications, HM hydraulic oil provides reliable performance without the need for viscosity index improvers.
When HV hydraulic oil is the correct choice
HV hydraulic oil is typically selected where:
- Equipment operates across wide temperature ranges
- Cold starts occur at low ambient temperatures
- Oil temperature rises significantly during operation
- The manufacturer permits or specifies HV oils
HV oils are often preferred for mobile equipment, outdoor installations, and systems exposed to seasonal temperature changes.
Is HV hydraulic oil better than HM
No. HV hydraulic oil is not inherently better than HM hydraulic oil.
HV oils solve temperature related viscosity problems. If temperature variation is not an issue, HM hydraulic oil may be entirely appropriate and may offer better shear stability in some applications.
The correct choice depends on operating conditions, not hierarchy.
HM and HV compared with AW hydraulic oil
AW is a market term indicating the presence of anti-wear additives.
In practice:
- Most oils sold as AW hydraulic oil fall under ISO 11158 HM
- HV hydraulic oils are also anti-wear oils
- AW does not distinguish between HM and HV
For technical specification, ISO classifications should always be used instead of market terminology.
Frequently asked selection questions
What is the difference between HM and HV hydraulic oil
HM and HV are ISO hydraulic oil categories. HV oils have higher viscosity index and maintain viscosity more consistently across temperature changes.
Can HV hydraulic oil replace HM
Sometimes, if permitted by the manufacturer and if temperature variation justifies its use.
Does HV hydraulic oil provide more wear protection
No. Both HM and HV oils are anti-wear oils. The difference is viscosity behaviour, not additive protection.
Related reference pages
For market terminology clarification, refer to What does AW mean on hydraulic fluid . For viscosity grade selection, refer to Which is better hydraulic oil ISO VG 32 or ISO VG 46 .
Technical support
If you require confirmation of the correct hydraulic oil category or viscosity grade for your equipment, technical support is available.
For product selection support, contact Sinopec Online or call +44 020 8068 3444.