Overview
EN ISO 4263-4:2006 - “Petroleum and related products - Determination of the ageing behaviour of inhibited oils and fluids - TOST test - Part 4: Procedure for industrial gear oils” (CEN/ISO) specifies a laboratory method to assess the ageing behaviour of industrial gear oils. The test accelerates oxidation by exposing oil samples to air and elevated temperatures and evaluates degradation after a defined period (312 h) using several chemical and physical endpoints. This part covers gear oils classified as CKC, CKD, CKS and CKT (per ISO 6743-6).
Key Topics and Requirements
- Test principle: Thermo-oxidative stability test (TOST) - oil samples reacted in presence of air, excluded from light, at specified temperatures depending on gear-oil category.
- Test temperatures: Typical temperatures are 95 °C (CKC), 121 °C (CKD) and 150 °C (CKS/CKT).
- Duration: Standard exposure time is 312 hours.
- Measured endpoints:
- Kinematic viscosity at 100 °C (change used to quantify degradation)
- Insoluble content (precipitation number)
- Acid number increase (where required)
- Sediment content by filtration
- Additive content variation
- Infra-red oxidation measurements
- Apparatus and controls:
- Oxidation cell: borosilicate tube ~600 mm length, 41 mm internal diameter, calibrated to 300 ml ±1 ml.
- Thermostatically controlled heating bath: maintain sample temperature to ±0.2 °C.
- Air supply and dryer, with flowmeters accurate for ~10 l/h ±0.5 l/h per cell.
- Specific reagents such as heptane and acetone; strong cleaning solutions (note hazard warnings for chromosulfuric acid).
- Sampling and cleanliness: Sampling per ISO 3170; detailed glassware cleaning and safety precautions are specified.
Applications and Users
This standard is used to support:
- Lubricant formulation and R&D - evaluate additive packages and base-oil stability.
- Quality control and batch release - confirm product ageing resistance and shelf-life performance.
- Failure analysis and root-cause investigations - determine oxidation-related degradation mechanisms.
- OEM and procurement specifications - provide repeatable test data for gear oil selection.
Primary users include lubricant manufacturers, independent testing laboratories, OEM drivetrain engineers, standards bodies, and procurement/specification teams.
Related Standards (if applicable)
- ISO 4263 (other parts): Part 1 (mineral oils), Part 2 (HFC hydraulic fluids), Part 3 (synthetic hydraulic fluids)
- ISO 6743-6 (gear oil classification)
- Normative references used in the method: ISO 3104 (viscosity), ISO 3170 (sampling), ISO 3696 (water for labs), ISO 12185 (density) among others.
Keywords: EN ISO 4263-4:2006, TOST test, industrial gear oils, ageing behaviour, kinematic viscosity, precipitation number, acid number, sediment by filtration, lubricant testing.
