Causes and Prevention of Hydraulic Oil Overheating in Machinery

Causes

If the amount of oil in the hydraulic tank is too low, the hydraulic system will not have sufficient flow to carry away the heat generated during operation, leading to increased oil temperature. This insufficient cooling affects all components, including those utilizing hydraulic jack fluid, which becomes particularly vulnerable to overheating when operating with inadequate fluid levels.

Prevention Measures

During actual operation and maintenance, strictly adhere to the oil level regulations specified in the operating procedures. Regularly check oil levels and top up with appropriate hydraulic oil or hydraulic jack fluid as needed.

Generally, oil should be changed after 1000 hours of cumulative operation. When changing oil, it is important not only to drain the old oil from the tank but also to replace the old oil in the entire system pipelines and working circuits. When adding oil, it is best to use a filter with 120 mesh or finer, and add sufficient oil according to regulations to ensure that the hydraulic fluid, including any hydraulic jack fluid in the system, has adequate circulation and cooling conditions.

In case of sudden failures caused by hydraulic oil contamination, the hydraulic system oil must be filtered or replaced immediately to prevent further damage and overheating issues.

Causes

Air entrained in hydraulic oil, including hydraulic jack fluid, will escape from the oil in low-pressure areas and form bubbles. When these bubbles move to high-pressure areas, they will be crushed by the high-pressure oil, undergo rapid compression, and release a large amount of heat, causing the oil temperature to rise. This phenomenon, known as cavitation, not only increases temperatures but also causes micro-pitting and erosion of component surfaces.

Prevention Measures

Regularly check the tightness of seals at oil inlet pipe connections and other sealing points to prevent air from entering the system. Additionally, after each oil change, it is essential to bleed all air from the system, including any components utilizing hydraulic jack fluid.

Proper bleeding procedures involve operating each hydraulic function slowly through its full range of motion multiple times, allowing trapped air to escape through the reservoir. This process is particularly important for hydraulic jack fluid systems, where air pockets can cause both overheating and erratic operation.

Maintain proper oil levels at all times, as low levels can introduce air into the system through the pump intake. Inspect suction lines for cracks or loose connections that could draw air into the system, and replace any damaged components immediately.

Causes

Construction site environments are often harsh, and as machinery operating time increases, hydraulic oil, including hydraulic jack fluid, easily becomes contaminated with impurities and dirt. Contaminated hydraulic oil passing through the clearance between pumps, motors, and valves can scratch and damage the precision and roughness of mating surfaces, increasing leakage and raising oil temperature.

Even small particles can cause significant damage in hydraulic systems. Particles as small as 5 microns can embed themselves in critical surfaces, acting as abrasives that accelerate wear. This wear creates larger clearances, leading to increased internal leakage, which in turn generates more heat in the system.

Prevention Measures

Establish a regular oil analysis program to monitor contamination levels in both system oil and hydraulic jack fluid. This allows for proactive maintenance before excessive contamination causes damage or overheating.

Implement proper filtration practices throughout the system's life cycle, from initial filling to regular maintenance. Use clean containers and funnels when adding or changing hydraulic oil or hydraulic jack fluid, and always filter new oil before introducing it into the system.

Maintain a clean environment around hydraulic reservoirs and fill points. Use caps and plugs to prevent contamination when components are removed for service. Consider installing additional filtration, such as kidney-loop filtration systems, for equipment operating in extremely harsh environments.

When contamination-related failures occur, thoroughly flush the entire system before refilling with new hydraulic oil or hydraulic jack fluid. Simply draining and refilling will not remove contaminants trapped in lines and components.

Causes

Using hydraulic oil with incorrect brand, quality, or viscosity grade, or mixing different grades of hydraulic oil, can result in an inappropriate viscosity index. If the oil viscosity is too high, power loss increases and oil temperature rises. If the viscosity is too low, leakage increases, which also causes oil temperature to rise. This is particularly critical for hydraulic jack fluid, where proper viscosity is essential for both lifting performance and temperature control.

Temperature extremes can exacerbate the problems caused by improper oil selection. Oil that performs adequately in moderate temperatures may become too thick in cold conditions, causing excessive pressure drops and heat generation, or too thin in hot conditions, leading to increased leakage and reduced lubrication.

Prevention Measures

Select hydraulic oil, including appropriate hydraulic jack fluid, according to the manufacturer's recommended specifications, taking into account the machine's operating environment and temperature factors. For machines with special requirements, use dedicated hydraulic oil as specified.

Consider seasonal variations when selecting hydraulic fluids. In regions with significant temperature changes, multi-viscosity oils that maintain proper viscosity across a wider temperature range may be beneficial. Always check compatibility before changing oil types, especially when selecting hydraulic jack fluid for specialized components.

When hydraulic components and systems are difficult to maintain, select high-performance anti-wear hydraulic oils that can better withstand contamination and temperature extremes. Keep detailed records of oil changes, including the type and quantity of oil added, to prevent accidental mixing of incompatible products.

Regularly test oil samples to verify that the hydraulic oil or hydraulic jack fluid is maintaining its specified properties. Oil degradation can occur over time, even with proper maintenance, requiring earlier-than-scheduled replacement.

Causes

Abrasive particles, impurities, and dust are adsorbed onto the filter element as they pass through the filter, increasing oil suction resistance and energy consumption, which in turn causes oil temperature to rise. A clogged filter can cause cavitation in the pump, leading to increased noise, reduced performance, and higher operating temperatures in all system components, including those using hydraulic jack fluid.

As filter elements become restricted, pressure drop across the filter increases. This not only reduces system efficiency but can cause the bypass valve to open, allowing unfiltered oil to circulate through the system, leading to increased contamination and accelerated wear.

Prevention Measures

Regularly clean and replace filters according to the manufacturer's recommendations. For filters with clogging indicators, clean or replace the filter element as indicated. The performance, structure, and service life of the filter element must meet its application requirements.

For example, a TY220 bulldozer continuously alarmed during operation, accompanied by smoke and a burning smell from the torque converter area, with a low oil level in the steering tank. The investigation revealed that a clogged suction filter in the torque converter return pump caused the failure. The blocked filter prevented oil leaking from the torque converter from being pumped back to the steering tank, causing it to accumulate. This increased resistance in the torque converter, generating more heat from friction and leading to rapid oil temperature rise. After cleaning the filter, the oil temperature returned to normal.

Establish a regular maintenance schedule for all filters in the hydraulic system, including those associated with hydraulic jack fluid circuits. Use only high-quality replacement filters that meet or exceed OEM specifications, as cheaper alternatives may not provide adequate filtration or may collapse under pressure.

Causes

High ambient temperatures, combined with prolonged high-load operation, can cause oil temperatures to rise excessively. In such conditions, the system's natural heat dissipation mechanisms cannot keep up with heat generation, leading to a continuous temperature increase in the hydraulic oil and hydraulic jack fluid.

Direct sunlight can further exacerbate the problem by heating hydraulic reservoirs and lines beyond the ambient air temperature. This creates a compounding effect where both the machinery workload and environmental conditions contribute to overheating.

Prevention Measures

Avoid prolonged continuous operation under heavy loads in high-temperature environments. If oil temperature becomes too high, allow the equipment to run idle for approximately 10 minutes to allow the oil temperature, including hydraulic jack fluid temperature, to decrease before resuming work.

Schedule heavy work during cooler parts of the day when possible, such as early morning or evening in hot climates. Provide shade for equipment when parked, and consider insulation for hydraulic reservoirs and lines exposed to direct sunlight.

In extreme conditions, supplemental cooling systems may be necessary. Monitor oil temperatures regularly during high-temperature operation, and be prepared to reduce workload or shut down temporarily if temperatures approach critical levels.

Ensure that all cooling system components are functioning properly, as their efficiency is even more critical in high ambient temperatures. Clean radiators and coolers frequently to maintain maximum heat dissipation capacity, which helps protect both the hydraulic system oil and hydraulic jack fluid from overheating.

Causes

Gear pumps' gears with pump bodies and side plates, cylinder blocks with valve plates in piston pumps and motors, cylinder bores with pistons, and valve spools with valve bodies in directional valves all rely on clearance sealing. Wear of these components will cause increased internal leakage and higher oil temperatures. This wear process can be accelerated by contaminated oil or improper hydraulic jack fluid selection.

As clearances increase due to wear, more fluid flows through these enlarged gaps, creating additional turbulence and friction that generates heat. This creates a vicious cycle where increased heat accelerates oil degradation, which in turn increases wear rates and heat generation.

Prevention Measures

Promptly repair or replace components with excessive wear. Statistics show that under normal conditions, imported hydraulic pumps and motors should be inspected after 5-6 years of operation, while domestic products typically require inspection after 2-3 years. Timely maintenance is essential to prevent further damage.

Without proper maintenance, equipment may operate normally when cold but exhibit significantly reduced performance after 1-2 hours of operation as temperatures rise, requiring shutdowns to allow oil cooling before work can resume. This pattern is particularly noticeable in systems utilizing hydraulic jack fluid, where performance degradation becomes immediately apparent.

For example, after a WY160 hydraulic excavator exhibited these symptoms, testing revealed significantly low operating pressure in various mechanisms. Suspecting a problem with the main relief valve or main pump, technicians first inspected the main relief valve, finding no abnormalities. Subsequent inspection of the main pump revealed severe wear on the valve plate's spherical surface. After lapping the valve plate, reassembling with proper clearances, and refilling with appropriate hydraulic oil, the machine operated normally.

In another case, a ZL50 loader exhibited slow, weak operation. Testing revealed low system pressure, and technicians noted excessive heat from the gear pump—classic symptoms of internal wear causing leakage. Disassembly confirmed that the clearance between the gear pump side plates and gear end faces exceeded specifications. Replacing the gear pump resolved the issue, restoring proper operation and normal temperature levels in both the main hydraulic system and hydraulic jack fluid circuits.

Causes

Typically, water-cooled or air-cooled oil coolers are used for forced temperature reduction of hydraulic system oil. For water-cooled coolers, the heat transfer coefficient can decrease due to dirty heat sink fins or poor water circulation. For air-cooled coolers, excessive oil contamination can block the gaps between the cooler's heat sink fins, preventing effective heat dissipation by the fan, resulting in increased oil temperatures throughout the system, including in hydraulic jack fluid components.

Cooling system fans or pumps that fail to operate at proper speeds can significantly reduce cooling capacity. Similarly, thermostat failures in some cooling systems can prevent the cooler from engaging when needed, allowing temperatures to rise unchecked.

Prevention Measures

Implement a regular inspection and maintenance program for the hydraulic oil cooling system. Check coolant levels and quality in water-cooled systems, and ensure proper flow rates. For air-cooled systems, regularly clean fins and verify fan operation.

Establish a schedule for cleaning heat exchangers based on operating conditions. Equipment working in dusty or dirty environments may require more frequent cleaning. Use appropriate methods for cleaning—compressed air for light contamination, and low-pressure water with mild detergents for heavier deposits.

Inspect hoses and connections for signs of wear, leaks, or blockages that could reduce cooling system efficiency. Ensure that bypass valves are functioning correctly to prevent oil from circumventing the cooler when it should be passing through.

Monitor temperature differentials across the cooler to detect reduced efficiency before overheating occurs. A significant decrease in the temperature drop between inlet and outlet indicates a need for maintenance. Address any cooling system issues immediately to prevent damage to the hydraulic system and ensure proper operating temperatures for all components, including those utilizing hydraulic jack fluid.