Gear Oils / 5 min
Gear Oil Selection Guide: Viscosity, Additives and Application Conditions
Industrial reducers and enclosed gearboxes must transmit power reliably under high loads and demanding operating conditions. The right gear oil forms a solid protective film on gear teeth, reduces friction and carries away heat.
Published by: Rotek Technical Content Team
Content is published based on manufacturer technical documentation and equipment requirements as the basis for final selection. This is general guidance and does not replace equipment-specific manufacturer approval.
Review our editorial guidelinesTable of Contents
- - The Core Functions of Gear Oil
- - Choosing ISO VG Viscosity
- - The Role of EP (Extreme-Pressure) Additives
- - The Effect of Temperature and Operating Environment
- - Manufacturer Specifications (DIN 51517)
The Core Functions of Gear Oil
Gear oil forms a separating film between contacting tooth surfaces, preventing metal-to-metal contact and wear. At the same time, it cools the heat generated by friction and protects against corrosion.
Choosing ISO VG Viscosity
ISO VG classification is used for gear oils. Reducers operating at low speed and high load require thicker oils (e.g. ISO VG 320 or 460), while systems running at higher speeds with lighter loads need thinner oils (e.g. ISO VG 150 or 220).
The Role of EP (Extreme-Pressure) Additives
In gears operating under shock and heavy load, oil film thickness alone cannot provide sufficient protection. EP (Extreme Pressure) additives form a protective layer on the gear surface through a chemical reaction, preventing welding and wear (micropitting) under high pressure.
The Effect of Temperature and Operating Environment
High operating temperatures cause the oil to oxidize (degrade) prematurely. In very hot environments or with long maintenance intervals, synthetic gear oils (PAO or PAG-based) with higher oxidation resistance should be preferred over mineral oils.
Manufacturer Specifications (DIN 51517)
Industrial gear oils are generally classified under the DIN 51517 standard. Part 3 (CLP) describes gear oils containing anti-wear and EP additives, and is frequently referenced by reducer manufacturers.
Frequently Asked Questions
Where is ISO VG 220 gear oil used?
ISO VG 220 gear oil is generally used in enclosed reducers operating at medium speed and medium-to-high load, in conveyor systems, and in standard industrial gearboxes. It's a widely preferred viscosity class.
What does CLP gear oil mean?
CLP is a term under the DIN 51517 standard describing industrial enclosed gear oils containing extreme-pressure (EP) additives, anti-corrosion and anti-oxidation additives. It's mandatory for heavily loaded systems.
Can hydraulic oil be used instead of gear oil?
No, hydraulic oil cannot substitute for gear oil. Hydraulic oils generally have lower viscosity and lack the dense EP additives that give gear oils their high load-carrying capacity.
When should synthetic gear oil be preferred?
Synthetic gear oil should be preferred where operating temperature is very high, where extreme loading occurs, where oil change intervals need to be extended, or where the system sits at a hard-to-reach point.
Why does gear oil foam?
Foaming in gear oil is generally caused by incorrect oil level, water entering the system, oil contamination, or the mixing of incompatible oils causing the anti-foam additives to lose their effect.