ISO 4263-2:2003

Overview

ISO 4263-2:2003 specifies the TOST (Thin‑Oil Oxidation Stability Test) procedure for assessing the accelerated ageing behaviour of category HFC hydraulic fluids (as defined in ISO 6743‑4 and ISO 12922). The standard defines a laboratory method that exposes fluid samples to oxygen, water and metal catalysts at elevated temperature and monitors chemical degradation by measuring pH and insolubles content until defined end-points are reached.

Key topics and requirements

• Test principle: accelerated ageing of HFC hydraulic fluids at controlled temperature with oxygen flow and a steel/copper catalyst coil; periodic sampling to measure degradation.
• End-points: test terminates when pH falls to 4.0, insolubles exceed 4.0% (m/m), or after 200 hours.
• Test conditions: oxidation cell heated to 95 °C (typical requirement), oxygen supplied (≥99.5% purity) at controlled flow, samples kept in the dark.
• Catalyst assembly: paired steel and copper wires are cleaned, wound to specified dimensions and stored/handled to avoid contamination.
• Analytical measurements: pH measurement and determination of insolubles (using a specified filter medium, oven-drying and analytical balance) are used to follow degradation.
• Apparatus & reagents: oxidation cell and mushroom condenser, thermostatic heating bath, flowmeter, syringes/pipettes, membrane filters (0.4 µm), heptane, acetone, propan‑2‑ol and cleaning solutions; water quality per ISO 3696.
• Cleaning, sampling and handling: detailed procedures for glassware cleaning, catalyst preparation and sample collection; safety warnings for oxygen use and hazardous materials.
• Normative references: includes links to ISO 3170 (sampling), ISO 20843 (pH of fire‑resistant fluids), ISO 3696 (water quality), and related ISO 4263 parts.

Applications and users

ISO 4263-2 is used to:

• Evaluate oxidative stability and ageing behaviour of HFC (water‑glycol) hydraulic fluids.
• Support product development and formulation screening for manufacturers of fire‑resistant hydraulic fluids.
• Provide laboratory test data for quality control, specification compliance, shelf‑life assessment and procurement requirements.
• Assist OEMs, hydraulic system engineers, test laboratories and regulatory/standards bodies in comparing fluid performance under accelerated oxidative conditions.

Typical users: fluid formulators, independent testing laboratories, fleet maintenance engineers, OEM specification writers and procurement teams.

Related standards

• ISO 4263‑1, ISO 4263‑3, ISO 4263‑4 (other TOST procedures for mineral oils, synthetic fluids, gear oils)
• ISO 6743‑4 and ISO 12922 (classification and specification of hydraulic fluids)
• ISO 3170, ISO 3696, ISO 20843 (sampling, water quality, pH measurement)

Keywords: ISO 4263-2:2003, TOST test, ageing behaviour, HFC hydraulic fluids, hydraulic fluid ageing, oxidation test, catalyst coil, pH measurement, insolubles content, fire‑resistant hydraulic fluids.