How to deal with hydraulic oil discoloration?

Discoloration of hydraulic oil is usually caused by oxidation, contamination, or wear of internal components. Appropriate treatment measures need to be taken according to the specific cause. The following are detailed treatment steps and suggestions:

Preliminary judgment of the cause of discoloration

- Oxidation and deterioration: the oil turns black, the viscosity increases, and there is a burnt smell (common in high temperature or long-term use).

- Contamination:

- Water mixing: the oil is milky white and turbid (may be due to cooler leakage or a humid environment).

- Dust/metal particles: the oil is gray or has suspended impurities (filter failure or component wear).

- Mixed with other oils: abnormal color (such as mistakenly adding different types of oil).

- Component wear: there are copper chips (pump/motor wear) or rust (pipeline corrosion) in the oil.

Treatment steps

(1) Shutdown inspection

- Stop the equipment immediately to avoid further damage.

- Check whether the hydraulic system has leaks, overheating, or abnormal noise.

(2) Oil testing

- Visual/olfactory inspection: observe color, transparency, and odor.

- Professional oil analysis (if conditions permit): test water content, particulate matter, acid value and other indicators.

(3) Targeted treatment

- Severe oxidation or contamination:

- Completely ｒｅｐｌａｃｅ the hydraulic oil: drain the old oil, clean the oil tank, pipes, and filter element.

- ｒｅｐｌａｃｅ the filter: ｓｅｌｅｃｔ a high-precision filter element (such as ISO 4406 standard 18/16/13).

- Water mixing:

- Use an oil-water separator or centrifugal dehydration equipment.

- Check the cooler and seals for leaks.

- Metal particle contamination:

- Check for worn parts (such as pumps, valves, and cylinders), and repair or ｒｅｐｌａｃｅ them.

- Install a magnetic filter in the return oil line to absorb iron filings.

- Oil mixing problem:

- ｒｅｐｌａｃｅ the oil with the correct type after thoroughly cleaning the system.

(4) System cleaning

- Use new oil of the same type or special flushing oil to circulate and flush the system until there are no residual impurities.

- Focus on cleaning the oil tank (remove bottom sediment) and the oil suction line.

(5) Preventive measures

- Control oil temperature: Install a cooler to ensure that the temperature is ≤60℃ (avoid oxidation).

- Strengthen sealing: Regularly check pipes, joints, and hydraulic cylinder seals.

- Regular maintenance:

- ｒｅｐｌａｃｅ oil and filter elements according to the cycle (refer to the equipment manual).

- Keep the oil tank vents dry (use desiccant or an air filter).

- Avoid oil mixing: Hydraulic oils of different brands/models cannot be mixed.

When to seek professional help?

- Repeated discoloration of the oil or frequent system failures.

- Severe wear is found (such as loud pump noise, weak actuator).

- When the source of pollution cannot be determined.

Precautions

- Waste hydraulic oil must be handled by environmental protection requirements and cannot be discharged at will.

- Ensure that the system is thoroughly clean when changing the oil to avoid cross-contamination between new and old oil.

The above measures can effectively solve the problem of hydraulic oil discoloration and extend the life of the system. If the problem is complicated, it is recommended to contact the hydraulic system service provider for diagnosis.