Bobcat 825 A Durable Classic with Fluid System Challenges

[MikePhua]

The Bobcat 825 and Its Historical Footprint
The Bobcat 825 skid steer loader was introduced in the late 1970s by Melroe Manufacturing Company, which later became part of the Bobcat brand under Clark Equipment and eventually Doosan. Designed as a mid-sized loader with robust hydraulic capabilities, the 825 was built for versatility in construction, agriculture, and industrial settings. It featured a rated operating capacity of approximately 1,500 lbs and was powered by a 4-cylinder diesel engine, typically sourced from Perkins or Kubota depending on production year.
Though exact sales figures are hard to trace, the 825 was widely adopted across North America and parts of Europe, especially in rental fleets and municipal yards. Its popularity stemmed from its mechanical simplicity, durable frame, and compatibility with a wide range of attachments. Even today, many units remain in service, often passed down through generations or restored by enthusiasts.
Terminology Clarification
- Hydraulic Reservoir: The tank that stores hydraulic fluid used to power the loader’s arms and attachments
- Chain Case: Enclosure housing the drive chains that transfer power from the engine to the wheels
- Spin-On Filter: A replaceable filter cartridge that screws onto a filter head, used to clean hydraulic fluid
- Auxiliary Hydraulics: Additional hydraulic ports used to power external attachments like augers or grapples
- Filter Cart: A portable unit with pumps and filters used to clean hydraulic systems without running the machine
Milky Hydraulic Fluid and Water Contamination
One of the most common issues in aging Bobcat 825 units is milky hydraulic fluid—a clear sign of water contamination. This condition can arise from several sources:

• Cracked fiberglass covers allowing rainwater intrusion
  
• Worn gaskets on the chain case or reservoir lid
  
• Condensation buildup in humid climates
  
• Improper storage without fluid checks
  

Water-contaminated hydraulic fluid compromises lubrication, corrodes internal components, and reduces system efficiency. In severe cases, it can lead to pump failure or erratic control response.
Drainage and Fluid Replacement Strategies
The Bobcat 825 holds approximately 27 gallons of hydraulic fluid, distributed across the reservoir, chain cases, cylinders, and hoses. Draining this fluid completely is challenging due to the machine’s design, which includes multiple low points and internal cavities.
Operators seeking a thorough flush often use the following approach:

• Disconnect a return hose and place it in a clean bucket
  
• Feed fresh fluid into the reservoir while running the machine briefly
  
• Repeat until the fluid exiting the hose runs clear
  

This method, while effective, can be messy and time-consuming. A more controlled alternative is using a filter cart with water-absorbing elements. These carts circulate fluid through specialized filters—such as Aqua-Zorb or similar products—that remove water and particulates without engaging the loader’s hydraulic pump.
Filter Selection and Micron Ratings
The Bobcat 825 typically uses two or more spin-on filters mounted under the fiberglass cover. These filters can be cross-referenced to modern equivalents from brands like Zinga or Donaldson. For water removal, filters ending in “AZ” (Aqua-Zorb) are recommended.
A staged filtration strategy is often employed:

• Start with a 10-micron water-absorbing filter to remove bulk contaminants
  
• Follow with a 3-micron filter to capture fine particles
  
• Replace stock filters after system cleanup
  

This approach ensures both water and debris are removed, extending the life of pumps, valves, and actuators.
Preventing Future Contamination
Once the system is clean, preventing recurrence is key. Recommended steps include:

• Replacing all reservoir and chain case gaskets with high-quality seals
  
• Inspecting the fiberglass cover for cracks or warping
  
• Installing a breather cap with a moisture trap
  
• Storing the machine indoors or under a tarp during wet seasons
  
• Performing fluid checks monthly, especially in humid regions
  

One operator in Kentucky reported recurring contamination until he replaced the chain case gasket and added a breather with a desiccant pack. Since then, his fluid has remained clear for over a year despite frequent outdoor use.
Auxiliary Hydraulics and Filter Integration
Some users consider integrating a filter head directly into the auxiliary hydraulic circuit. This allows for periodic fluid polishing without disassembly. Quick couplers make this setup easy to install and remove, and it can be used with standard spin-on filters or water separators.
While not factory-standard, this modification is increasingly popular among owners of legacy machines. It offers a low-cost way to maintain fluid quality and reduce wear on aging components.
Conclusion
The Bobcat 825 remains a testament to durable engineering and practical design. While its hydraulic system presents challenges—especially with fluid contamination—modern filtration solutions and proactive maintenance can keep it running smoothly. For operators willing to invest time and care, the 825 offers reliable performance and a direct connection to the golden age of skid steer innovation. With proper attention to fluid health and system integrity, this classic loader can continue serving for decades to come.