Hitachi EX350 LC-5 Excavator Reliability and Hydraulic Troubleshooting

[MikePhua]

The Legacy of the EX350 LC-5 Series
The Hitachi EX350 LC-5 was part of Hitachi’s fifth-generation excavator lineup, introduced in the late 1990s as a refinement of the proven EX series. Built for heavy-duty excavation, demolition, and site preparation, the EX350 LC-5 combined Japanese engineering precision with North American market demands for durability and serviceability. The “LC” designation refers to its long carriage, offering improved stability for deep trenching and heavy lifting.
Hitachi Construction Machinery, founded in 1970, had already established a strong global presence by the time the EX350 LC-5 entered production. The model was widely adopted in infrastructure projects across Canada, the U.S., and Southeast Asia, with thousands of units sold before being succeeded by the ZX series.
Core Specifications and Performance Profile

• Operating weight: Approximately 35,000 kg
  
• Engine: Isuzu AA-6HK1X, 6-cylinder turbocharged diesel
  
• Net power: 246 HP (183 kW)
  
• Hydraulic flow: Dual variable displacement piston pumps
  
• Bucket capacity: 1.4–2.1 cubic meters depending on configuration
  
• Maximum digging depth: 7.5 meters
  
• Swing speed: 9.5 rpm
  
• Travel speed: Up to 5.5 km/h
  
• Fuel tank capacity: 620 liters
  

The EX350 LC-5 was known for its smooth hydraulic response, robust undercarriage, and balanced weight distribution. Its long carriage allowed operators to work confidently on slopes and soft ground, while the Isuzu engine delivered consistent torque under load.
Hydraulic System Behavior and Troubleshooting
One of the most discussed issues with aging EX350 LC-5 units is inconsistent hydraulic performance. Symptoms include:

• Slow boom or stick movement
  
• Weak travel power
  
• Intermittent swing function
  
• Engine bogging under hydraulic load
  
• No fault codes or warning lights
  

These issues often stem from a combination of wear, contamination, and control logic degradation. The EX350 LC-5 uses a load-sensing hydraulic system with pilot-operated valves and electronic pump control. When pilot pressure is compromised or the pump control logic fails, the system defaults to low-flow or bypass mode.
Key diagnostic steps:

• Check pilot pressure at the control valve block (target: 400–500 psi)
  
• Inspect pilot filters and screens for debris
  
• Test pump solenoids for voltage and resistance
  
• Verify pump displacement control via manual override
  
• Inspect travel motor case drain for excessive flow (indicates internal leakage)
  

A contractor in Alberta reported that his EX350 LC-5 lost travel power after a cold snap. After testing pilot pressure and finding it low, he replaced a clogged pilot filter and restored full function. He now includes pilot filter inspection in his monthly service routine.
Electrical and Sensor Vulnerabilities
The EX350 LC-5 relies on several sensors and solenoids to manage hydraulic flow:

• Pump pressure sensors
  
• Engine speed sensor
  
• Hydraulic oil temperature sensor
  
• Pump control solenoids (typically two per pump)
  

Failures in these components can mimic mechanical issues. For example, a faulty engine speed sensor may cause the pump controller to reduce flow, assuming the engine is under strain. Similarly, a stuck solenoid can prevent pump displacement from increasing under load.
Solutions:

• Use a multimeter to test sensor voltage and continuity
  
• Replace solenoids with OEM-rated units
  
• Clean connectors and apply dielectric grease
  
• Check controller ground and power supply
  

Some operators retrofit manual pump control switches to override electronic logic during troubleshooting. While effective short-term, this bypass should be removed once the root cause is resolved.
Preventive Maintenance and Reliability Strategies
To extend the life of the EX350 LC-5:

• Change hydraulic filters every 500 hours
  
• Flush hydraulic oil every 2,000 hours or annually
  
• Inspect pilot lines and fittings quarterly
  
• Monitor fuel quality and replace filters every 250 hours
  
• Grease all pivot points weekly
  
• Check undercarriage wear monthly, especially track tension and roller condition
  

Using ISO 46 hydraulic oil with anti-wear additives improves pump longevity. In cold climates, switching to low-viscosity hydraulic fluid during winter reduces startup strain.
Operator Tips and Field Adaptation
To optimize performance:

• Warm up hydraulics for 10–15 minutes before heavy digging
  
• Avoid sudden directional changes during travel
  
• Use boom and stick simultaneously to balance pump load
  
• Monitor engine RPM during swing and travel—bogging indicates pump overload
  
• Keep cab electronics clean and dry to prevent controller faults
  

Operators in Southeast Asia often install additional hydraulic coolers to combat high ambient temperatures. In one case, a mining crew in Indonesia extended pump life by 30% after adding a fan-cooled cooler and switching to synthetic hydraulic oil.
Conclusion
The Hitachi EX350 LC-5 remains a respected workhorse in the heavy excavation world. While hydraulic and electronic issues may arise with age, they are typically solvable with methodical diagnostics and preventive care. Its long carriage, responsive hydraulics, and durable frame make it a reliable choice for contractors who value performance and serviceability. With proper maintenance and thoughtful upgrades, the EX350 LC-5 continues to move earth with precision and power—decades after its debut.