Overview
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" specifies a laboratory method to determine the accelerated ageing behaviour of industrial gear oils (categories CKC, CKD, CKS, CKT as defined in ISO 6743-6). The standard uses controlled exposure to air and elevated temperatures to evaluate oil degradation over a 312 h test period and reports changes in kinematic viscosity, insoluble content (precipitation number) and other indicators of oxidation and additive depletion.
Key topics and technical requirements
- Scope: Gear oils in categories CKC, CKD, CKS and CKT.
- Test principle: Oxidative ageing in glass oxidation cells under air flow and elevated temperature; end-point after 312 h ± 2 h.
- Temperature by oil type:
- CKC: 95 °C
- CKD: 121 °C
- CKS / CKT: 150 °C
- Air flow: 10 L/h ± 0.5 L/h per cell (air dried and oil-free).
- Primary measurements:
- Kinematic viscosity at 100 °C (ISO 3104) - report increase after ageing.
- Insoluble content / precipitation number (Annex B) - quantify precipitate after solvent treatment and centrifugation.
- Visual rating of deposits and adhesivity on the tube walls.
- Optional/augmenting analyses:
- Acid number increase (ISO 6618 / ISO 6619).
- Sediment content by filtration (Annex C).
- Additives content variation (Annex D).
- Infra‑red oxidation (IR spectrum, measure absorbance at 1 710 cm‑1; Annex E).
- Apparatus & preparation: Borosilicate oxidation cell (300 ml oil), thermostatted heating bath, flowmeters, air dryer, calibrated thermometers, and strict glassware cleaning procedures (warning on chromosulfuric acid disposal and safety).
- Reporting: Results expressed as viscosity increase, precipitation-number change, deposit severity/adhesivity and any additional test outcomes.
Applications and who uses it
- Lubricant manufacturers - R&D and formulation optimisation for oxidation resistance and additive performance.
- Quality control & certification labs - routine batch testing and conformity to purchasers’ specifications.
- OEMs and gear designers - verifying gear oil suitability and expected ageing behaviour for industrial gearboxes.
- Procurement and asset managers - specifying minimum ageing resistance and shelf-life criteria.
- Failure analysis teams - investigating oxidation-related lubricant degradation and deposits.
Keywords: ISO 4263-4:2006, TOST test, industrial gear oils, ageing behaviour, kinematic viscosity, precipitation number, oxidation cell, gear oil testing, accelerated ageing.
Related standards
For laboratories and engineers specifying or testing gear oils, ISO 4263-4:2006 provides a reproducible TOST procedure to assess oxidative stability and practical ageing indicators used in product development, quality control and procurement.
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