Replacing the Water Pump on a Kobelco SK135SRLC Excavator

[MikePhua]

The Kobelco SK135SRLC and Its Cooling System
The Kobelco SK135SRLC is a short-radius hydraulic excavator designed for urban and confined job sites. Introduced in the early 2000s, it features a compact tail swing, efficient hydraulic circuitry, and a fuel-efficient Isuzu engine. Kobelco, founded in Japan in 1930, has long been recognized for its innovation in crawler excavators, and the SK135 series has been a strong seller across North America and Asia, especially in utility and roadwork sectors.
The cooling system in the SK135SRLC relies on a belt-driven water pump to circulate coolant through the engine block and radiator. This pump is critical for maintaining optimal operating temperature and preventing engine damage due to overheating. When the water pump fails—whether due to bearing wear, seal leakage, or impeller damage—replacement becomes urgent.
Identifying the Correct Water Pump
One of the challenges in sourcing a replacement pump for the SK135SRLC lies in the serial number range. Kobelco used different water pump configurations depending on the production batch. Machines with early serial numbers, such as YH01-00892, typically require a different pump than later models. The pumps may appear similar externally but differ internally in impeller design, bolt pattern, or housing dimensions.
Terminology:

• Serial number (S/N): A unique identifier for each machine, used to determine parts compatibility
  
• Impeller: A rotating component inside the pump that moves coolant through the system
  
• Housing: The outer shell of the pump that mounts to the engine block
  

For early serial numbers, Kobelco lists the water pump as part number VI136500181. However, this part may be backordered or discontinued. In such cases, a rebuild kit—such as VI1878121251—can be used if the original housing is intact.
Rebuild Kits vs. Full Replacement
Rebuild kits typically include:

• New bearings
  
• Shaft seals
  
• Impeller
  
• Gaskets
  
• Mounting hardware
  

If the pump housing is undamaged and the impeller shaft is not scored, rebuilding can be a cost-effective solution. However, rebuilds require precision and clean working conditions. Improper installation can lead to premature failure or coolant leaks.
Best practices:

• Clean all mating surfaces thoroughly
  
• Use torque specs from the service manual
  
• Apply thread sealant where specified
  
• Pressure test the cooling system after installation
  

In one Florida-based repair, a technician opted for a rebuild kit due to part availability. After careful assembly and gasket seating, the pump performed flawlessly under load.
Engine Model and Dealer Support
The SK135SRLC is powered by an Isuzu engine, and in many cases, the water pump is an Isuzu-sourced component. If Kobelco parts are unavailable, contacting an Isuzu industrial engine dealer may yield faster results. However, engine serial numbers are required to match the correct pump variant.
Steps to identify the engine:

• Locate the engine plate near the valve cover or timing case
  
• Record the model and serial number
  
• Cross-reference with Isuzu’s parts database or dealer catalog
  

In one case, a technician found that the Kobelco part number did not cross-reference with Isuzu’s catalog, but the engine serial number allowed the dealer to locate a compatible pump from stock.
Urgency and Field Downtime
Water pump failure can halt operations entirely. Without coolant circulation, the engine will overheat within minutes of load application. For contractors working in high-temperature regions or on tight schedules, downtime due to cooling system failure can be costly.
Preventative measures:

• Inspect pump bearings and seals during routine service
  
• Replace coolant every 1,000 hours or annually
  
• Monitor for leaks around the pump housing and weep hole
  
• Listen for bearing noise or grinding during startup
  

In one municipal fleet, proactive pump replacement every 3,000 hours reduced unplanned downtime by 40% over a three-year period.
Conclusion
Replacing the water pump on a Kobelco SK135SRLC requires attention to serial number, engine model, and part compatibility. Whether using a rebuild kit or sourcing a new pump, technicians must ensure proper installation and cooling system integrity. With the right part and careful assembly, the SK135SRLC can return to full operation—ready to dig, lift, and swing without overheating. In the world of excavators, a silent pump is a sign of a job well done.