The selection of hydraulic oil for excavators directly affects the stability, service life, and operational efficiency of the hydraulic system. Improper selection can easily lead to hydraulic pump wear, pipeline blockage, movement jams, and even system failures. The selection must be based on four core requirements—"viscosity adaptation, performance compliance, scenario matching, and compliance"—and comprehensively determined by combining equipment characteristics and operating environments. The specific requirements are as follows:

I. Core Requirement 1: Viscosity Must Match the Equipment and Ambient Temperature (Fundamental Premise)

Viscosity is the most critical indicator of hydraulic oil. Excessively high viscosity increases resistance in the hydraulic system (resulting in slower movements and higher fuel consumption), while excessively low viscosity reduces lubricity (accelerating wear of hydraulic pumps and valves, and even causing leaks). When selecting hydraulic oil, both "equipment requirements" and "ambient temperature" must be satisfied:

1. Prioritize the Viscosity Grade Specified in the Equipment Manual

Excavator manufacturers clearly recommend viscosity ranges based on the hydraulic system (e.g., pump type, pressure level), with common ones being ISO viscosity grades (such as ISO VG32, VG46, VG68):

• For medium and small-tonnage excavators (10-20 tons), ISO VG46 is mostly recommended (it has a wide application range, balancing low-temperature fluidity and high-temperature stability);

• For large-tonnage excavators (over 30 tons, with higher hydraulic system pressure) or high-temperature operating scenarios, ISO VG68 may be recommended (it has higher viscosity and stronger shear resistance, preventing oil film rupture under high pressure);

• For low-temperature operations (ambient temperature below -10°C), ISO VG32 or low-temperature-specific hydraulic oil (such as HV or HS grades) should be selected to ensure the hydraulic oil can flow quickly during winter startup and avoid movement jams caused by excessively high viscosity.

2. Dynamically Adjust Based on Ambient Temperature

• Summer/high-temperature areas (ambient temperature above 30°C): If the equipment recommends VG46, VG68 with slightly higher viscosity (or summer-specific hydraulic oil) can be selected to prevent excessive viscosity reduction at high temperatures and ensure lubricity;

• Winter/low-temperature areas (ambient temperature below 0°C): Hydraulic oil with low low-temperature viscosity (such as VG32 or hydraulic oil marked with "low-temperature fluidity") should be selected. If necessary, replace it with "low-temperature anti-wear hydraulic oil" (e.g., low-temperature type of HM anti-wear hydraulic oil) to prevent the hydraulic oil from solidifying or having poor fluidity at low temperatures, which would cause the system to fail to start normally.

II. Core Requirement 2: Must Meet Key Performance Indicators Such as "Anti-Wear Properties" to Protect the Hydraulic System

The hydraulic system of excavators operates at high pressure (usually 20-35MPa) and faces high risks of component wear. Hydraulic oil must have targeted performance, with anti-wear properties being the core, followed by anti-emulsification, anti-oxidation, and anti-foaming properties:

1. Anti-Wear Properties: Top Priority

Hydraulic pumps (such as piston pumps and gear pumps) are core components of the system. During operation, the metal surfaces rely on hydraulic oil to form an "oil film" for lubrication. Insufficient anti-wear properties will cause the oil film to rupture easily, leading to wear of the pump body and valve cores, and triggering faults such as leaks, pressure drops, and weak movements. When selecting, look for "anti-wear hydraulic oil" (coded as HM, with the international standard being ISO 11158). This type of oil contains anti-wear additives (such as zinc-based compounds), which can form a stable oil film under high pressure to reduce wear. The use of ordinary hydraulic oil (e.g., L-HL type) or engine oil as a substitute is prohibited— the former has insufficient anti-wear properties, while the latter has mismatched viscosity and additives, which will accelerate system damage.

2. Anti-Emulsification Properties: Prevent Damage to the System from Water

During operations in mountainous areas or rainy days, moisture can easily seep into the hydraulic system through breathing holes and seals. If the hydraulic oil has poor anti-emulsification properties, moisture will mix with the oil to form an "emulsion" (the oil becomes turbid), which not only damages the oil film and accelerates wear but also causes rust on metal components (such as hydraulic valves and pipeline inner walls) and even clogs filters. When selecting, pay attention to the "anti-emulsification grade" (e.g., GB/T 7305 standard, which requires oil-water separation time to be no more than 30 minutes). Prioritize HM-type hydraulic oil marked with "anti-emulsification". Regularly check the color of the hydraulic oil— if it changes from transparent to yellow or turbid, promptly test the moisture content and replace the oil if it exceeds the standard.

3. Anti-Oxidation and Anti-Foaming Properties: Extend Oil Service Life and Ensure System Stability

• Anti-oxidation: Hydraulic oil operates at high temperatures for a long time (the system operating temperature can reach 60-80°C) and is prone to reacting with air to oxidize and deteriorate, producing sludge and carbon deposits that clog filters and oil circuits, leading to abnormal system pressure. High-quality HM hydraulic oil contains antioxidants, which can extend its service life (usually 2000-3000 hours, while inferior oil may deteriorate after 1000 hours).

• Anti-foaming properties: During the operation of the hydraulic system, air is easily mixed into the oil to generate bubbles. Poor anti-foaming properties will prevent bubbles from bursting quickly, leading to "cavitation" (hydraulic pump suction, movement jams, and increased noise). When selecting, ensure the hydraulic oil meets the "anti-foaming standard" (e.g., ISO 6247, which requires foam volume to disappear within a specified time).

III. Core Requirement 3: Adapt to the Special Needs of Operating Scenarios (Avoid a "One-Size-Fits-All" Approach)

Different operating scenarios (such as mines, low-temperature environments, and plateaus) have additional requirements for hydraulic oil, which must be selected accordingly:

1. Heavy-Load/Mine Operations: Enhance "Shear Resistance"

During mining and hard rock excavation, the hydraulic system operates under high load and high-frequency movements for a long time, and the hydraulic oil is subjected to high shear forces (e.g., fast flow rate when passing through valves, which easily shears oil molecules). Insufficient shear resistance will cause the viscosity to decrease rapidly, resulting in loss of lubricity. It is necessary to select "high-shear-resistance anti-wear hydraulic oil" (e.g., "heavy-load type" of HM anti-wear hydraulic oil) or hydraulic oil that meets the excavator manufacturer’s "mine-specific" standards (such as special oil for brands like Komatsu and Caterpillar). This type of oil has a more stable molecular structure, can resist high-frequency shearing, and maintain stable viscosity.

2. Low-Temperature/Plateau Operations: Prioritize "Low-Temperature Fluidity"

In plateau low-temperature environments (e.g., below -20°C in winter), ordinary hydraulic oil will have poor fluidity due to a sharp increase in viscosity, making it difficult for the hydraulic pump to suck oil and even preventing startup. "Low-temperature anti-wear hydraulic oil" (such as HV or HS grades, complying with the GB/T 11118.1 standard) should be selected:

• HV grade: Suitable for -20°C to 40°C, with good low-temperature fluidity;

• HS grade: Suitable for -30°C to 40°C, with better low-temperature performance, making it suitable for extremely cold areas.

At the same time, note that before low-temperature operations, it is recommended to start the engine and idle it for 5-10 minutes to allow the hydraulic oil temperature to rise and viscosity to decrease before operation, avoiding system overload during cold startup.

3. Long-Term Continuous Operations: Focus on "Thermal Stability"

In large-scale infrastructure and tunnel operations, excavators need to work continuously for 8-12 hours, and the hydraulic system temperature is prone to rise (possibly exceeding 80°C). Poor thermal stability of hydraulic oil will accelerate oxidation and deterioration, shortening the replacement cycle. "High-temperature stable HM hydraulic oil" should be selected— its additives can maintain activity at high temperatures to reduce sludge formation. At the same time, regularly check the hydraulic oil radiator (clean dust to ensure normal heat dissipation) to prevent excessive oil temperature.

IV. Core Requirement 4: Compliance and Usage Taboos (Avoid Misselection and Misuse)

1. Choose Regular Brands and Standards; Reject Inferior Oil

Although inferior hydraulic oil (such as recycled oil and non-standard oil) is cheap, it has insufficient additives and many impurities, which can cause: ① Poor anti-wear properties, leading to hydraulic pump wear within 3-6 months; ② Impurities clogging filters, resulting in system pressure drop; ③ Rapid oxidation, requiring frequent replacement and thus increasing costs. When selecting: ① Choose well-known brands (such as Shell, Mobil, Great Wall) or excavator original factory-recommended oil (such as special hydraulic oil for Sany and XCMG); ② Check the packaging labels (whether there are ISO viscosity grades, HM anti-wear marks, production dates, and quality certificates) to avoid purchasing "three-no products" (no manufacturer, no production date, no quality certificate) without labels.

2. Prohibit Mixing Different Types/Brands of Hydraulic Oil

Different brands and types of hydraulic oil may have conflicting additive components (such as anti-wear agents and antioxidants). Mixing them will cause the additives to fail, producing precipitates or colloids that clog oil circuits. If it is necessary to replace the brand or type, the old oil must be completely drained first (including residual oil in the hydraulic oil tank, pipelines, and hydraulic pump). Flush the system 1-2 times with new oil before adding new oil to prevent residual old oil from affecting the performance of the new oil.

3. Regularly Test Oil Condition and Replace Hydraulic Oil Promptly

The service life of hydraulic oil is not fixed (it is affected by operation intensity and environment), so regular checks are required: ① Appearance (changes from transparent to light yellow, dark brown, then black; replace if it turns black); ② Viscosity (rub the oil between fingers— if the viscosity decreases significantly or there are impurity particles, replace it); ③ Moisture (drop a small amount of oil on a hot iron plate— a "sizzling" sound indicates excessive water content). Generally, it is recommended to replace the oil every 3000 hours for light-load operations, every 2000 hours for heavy-load/harsh environments, and no later than 1 year at most (even if the time limit is not reached, the oil may oxidize and deteriorate).

Conclusion

The selection logic for excavator hydraulic oil is as follows: First, determine the viscosity and type (prioritize HM anti-wear type) according to the equipment manual; then adjust the viscosity grade based on the ambient temperature; finally, supplement special needs according to the operating scenario (e.g., select HV grade for low temperatures, high-shear-resistance type for heavy loads). At the same time, reject inferior oil, do not mix different types of oil, and replace the oil regularly. Only by meeting these requirements can the stable operation of the hydraulic system be ensured, faults be avoided, and the service life of the equipment be extended.