The thermal stability of hydraulic oil is usually determined by thermal oxidation test or oxidation stability test. The following are commonly used measurement methods and equipment recommendations:
- Thermal stability measurement method
✅ ASTM D2070 (thermal stability test of hydraulic oil)
✅ ASTM D2272 (rotating oxygen bomb test, RBOT)
✅ ASTM D2893 (high temperature oxidation test, suitable for industrial lubricants)
- Equipment suitable for thermal stability test of hydraulic oil
| Test items | Recommended equipment | Purpose |
| Hydraulic oil thermal stability test (ASTM D2070) | Hydraulic oil thermal stability tester | Test the oxidation stability of hydraulic oil at high temperature |
| Rotating oxygen bomb test (RBOT) (ASTM D2272) | RBOT rotating oxygen bomb oxidation stability tester | Predict the antioxidant life of hydraulic oil |
| High temperature oxidation test (ASTM D2893) | Lubricating oil oxidation stability tester | Test the stability of hydraulic oil under long-term use at high temperature |
| Sediment evaluation | High-speed centrifuge + filtration equipment | Evaluate the sediment content of oil after thermal oxidation |
- Equipment recommendation
If you need to test the thermal stability of hydraulic oil, it is recommended to use the following equipment: 1️⃣ Hydraulic oil thermal stability tester (ASTM D2070)
Applicable to evaluate the thermal oxidation stability of hydraulic oil
The equipment includes a heating system and a metal catalyst
2️⃣ Rotating Oxygen Bomb (RBOT) Tester (ASTM D2272)
Used to predict the antioxidant capacity of hydraulic oil
Accelerate the oxidation process by pressurized oxygen and catalyst
3️⃣ High Temperature Oxidation Tester (ASTM D2893)
Applicable to long-term high temperature oxidation experiments
Can evaluate the viscosity growth and deposit formation of hydraulic oil
Hydraulic Oil Thermal Stability Test (ASTM D2070)
ASTM D2070 is used to evaluate the thermal stability of hydraulic oil at high temperatures, especially to detect the deposits and oxidation degree of the oil after the oil comes into contact with a metal catalyst at a high temperature of 135°C.
- Test Principle
Hydraulic oil is heated at 135°C with copper and iron catalytic metal sheets for 168 hours (7 days), and then the following are measured: ✅ Sludge – filter to measure the mass of the sediment
✅ Color change (ΔColor) – evaluate the oxidation of the oil
✅ Viscosity change (ΔViscosity) – evaluate the viscosity increase caused by high temperature oxidation
✅ Acid value change (ΔTAN) – evaluate the degree of oxidation and acidification of the oil
- Test equipment
| Equipment name | Purpose |
| Hydraulic oil thermal stability tester (ASTM D2070) | Provides constant temperature heating and stirring functions |
| Glass test tube (with metal catalyst) | Contains hydraulic oil and metal sheet for oxidation experiment |
| Constant temperature bath (135°C ± 0.5°C) | Controls oil sample temperature |
| Filter device (microporous filter membrane) | Filters oil sample and measures sediment |
| Visible spectrophotometer | Measures color change |
| Rotational viscometer / Ubbelohde viscometer | Measures viscosity change |
| Acid value titration device | Measures acid value change after oxidation |
- Test steps
1️⃣ Preparation – Weigh 200mL of hydraulic oil sample, put it into a glass test tube, and add copper and iron catalyst sheets
2️⃣ Heating – Put the test tube into a 135°C constant temperature bath and keep it for 168 hours
3️⃣ Cooling – Take out the oil sample and cool it to room temperature
4️⃣ Filter sediment – Filter the oil and weigh the sediment mass (mg/100mL)
5️⃣ Measure color change (ASTM D1500)
6️⃣ Measure viscosity change (ASTM D445)
7️⃣ Measure acid value change (ASTM D664)
- Result judgment
Sediment > 1.0 mg/100mL → Poor thermal stability
Color change Δ>2 levels → Obvious oxidation
Viscosity increase > 10% → May affect the operation of the hydraulic system
Acid value increase > 0.5 mgKOH/g → Indicates that oxidation is intensified