What Causes Hydraulic Oil to Change Color?

Hydraulic oil is essential for power transmission in various machinery, including power steering systems, brakes, elevators, transmissions, excavators, industrial machinery, and aircraft controls. The quality of hydraulic oil is crucial, and a common concern is whether color change indicates a problem. Let’s explore this:

Causes of Hydraulic Oil Color Change

Hydraulic oil can change color due to:

1. Thermal Stress:
   • Hot Spots: Areas in the system where the oil gets excessively hot and then cools down can cause the oil to darken.
   • Bubble Bursts: Air bubbles moving from the reservoir to high-pressure areas like pumps or valves can also generate heat.
   • Solution: Analyze the oil with FTIR curves for thermal degradation and conduct root cause analysis to identify and mitigate heat sources.
2. Oxidation:
   • Chemical Reaction: Oxidation occurs when oil combines with oxygen, leading to increased acid content, corrosion, and higher viscosity.
   • Color Indicators: Antioxidants in the oil may cause color changes from light yellow to black.
   • Solution: Conduct oil analysis to check for increased viscosity and acid number, indicating oxidation. Replace oil if oxidation is detected.

Additional Factors

• Contaminants: Presence of catalytic metals, heat, oxygen, and water accelerates oxidation.
• System Pressure: High pressure increases oxidation rates due to higher viscosity and more entrained air.
• Storage: Protect oil from prolonged sun exposure to prevent oxidation and degradation.

High quality hydraulic oil on the market

UNIOIL HYDRAULIC HVI is premium quality hydraulic oil formulated from refined mineral oils and enhanced thermal stability and anti-wear additives, suitable for extreme pressure hydraulic systems, operation in harsh, high temperature conditions.

Characteristic

• Due to high viscosity index, high shear stability of the viscosity index technology, help to always maintain stable viscosity, suitable for heavy duty hydraulic systems, variable working temperature.
• Excellent anti-wear and anti-corrosion help to hydraulic system protect and prolong the life of equipment.
• Good thermal stability and resistance oxidation, prevent the sludge, deposits help to extend the oil life, gives a cleaner system and reduced frequency of filter changes.

Applications

• Designed for hydraulic systems require low viscosity change with fluctuating temperature, wide variations in temperature, high load and extended duration to use oil.
• Mobile hydraulic equipment in outdoor: Road and bridge construction machinery, heavy load construction machinery, construction trucks…
• Hydraulic systems with crew, vane, gear or piston pumps, used in wide temperature variations in industry.

Contact Unioil immediately for advice and support.