How to determine if hydraulic oil viscosity is appropriate？

As the owner of a long-arm excavator, you must be wondering if the viscosity of the hydraulic oil in your excavator is appropriate. Please contact dewanda for more information.

1. Check the Operating Condition of the Hydraulic System

Observe the Actuator Performance:

Properly viscous hydraulic oil enables smooth and responsive movements of actuators such as the hydraulic cylinders and motors on an excavator’s long arm. If the viscosity is too high, the actuators may respond slowly, be hard to start, or even stick under low temperatures. On the other hand, if the viscosity is too low, you may notice creeping, vibrations, or unstable movement, making it difficult for the actuators to perform precise actions.

Monitor System Pressure Fluctuations:

Improper oil viscosity can cause abnormal system pressure. When viscosity is too high, flow resistance increases, leading to higher pressure loss and possibly exceeding normal working pressure, causing the relief valve to open frequently. If the viscosity is too low, internal leakage may increase, reducing effective pressure and making it difficult to maintain the required working pressure, thereby reducing work efficiency.

2. Inspect the Oil's Appearance and Flow Characteristics

Check Color and Clarity:

Generally, new hydraulic oil has a uniform color and high transparency. Over time, due to aging or viscosity changes, the oil may darken and become less transparent. However, since discoloration can also result from contamination or oxidation, this method should only be used as a preliminary assessment and combined with other checks.

Test Flow Behavior:

Place a small amount of hydraulic oil on a clean glass plate and observe its flow. At the same temperature, properly viscous oil flows smoothly and spreads relatively quickly. High-viscosity oil flows slowly, appears thick, and may form strings when poured. Low-viscosity oil flows too quickly and appears watery.

3. Use Professional Testing Equipment

Viscometer Measurement:

This is the most accurate method. Common types of viscometers include capillary and rotational viscometers. Follow the instrument’s instructions to place a sample of hydraulic oil in the device and measure its viscosity at a specified temperature. Then compare the result with the oil's specification to determine if it falls within the recommended range. For example, commonly used hydraulic oil for excavators typically has a kinematic viscosity of 32–46 mm²/s at 40°C.

Compare Oil Temperature Trends:

Use an oil temperature sensor to monitor the hydraulic oil temperature during operation. If the viscosity is too high, the system generates more heat due to greater flow resistance, resulting in a faster temperature rise. If the viscosity is too low, although heat dissipation improves, increased leakage may reduce system efficiency and cause abnormal temperature fluctuations. Comparing these temperature readings with normal values can help determine if the oil viscosity is appropriate.

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