Replacing the Oil Cooler on a Bobcat S175 Skid Steer

[MikePhua]

The Bobcat S175 and Its Cooling System Design
The Bobcat S175 skid steer loader, produced in the early 2000s, is a mid-frame machine powered by a 2.0L Kubota V2003 diesel engine. Known for its compact size and versatility, the S175 became one of Bobcat’s best-selling models, widely used in construction, landscaping, and agriculture. Like most hydrostatic machines, it relies on a dedicated oil cooler to regulate hydraulic fluid temperature and prevent system overheating during continuous operation.
The oil cooler is mounted adjacent to the radiator and shares airflow from the engine-driven cooling fan. It plays a critical role in maintaining hydraulic oil viscosity and protecting components such as drive motors, pumps, and control valves.
Terminology Notes

• Oil Cooler: A heat exchanger that dissipates heat from hydraulic or engine oil using ambient air or coolant.
  
• Hydraulic Loop: The closed circuit through which hydraulic fluid circulates under pressure to power machine functions.
  
• Bypass Valve: A pressure-sensitive valve that allows fluid to bypass the cooler if it becomes clogged or during cold starts.
  
• Stacked Plate Cooler: A type of oil cooler made of thin metal plates stacked together to maximize surface area and heat transfer.
  

Common Failure Modes and Symptoms
Oil coolers in the S175 are prone to damage from debris, corrosion, and internal clogging. Over time, metal fatigue or vibration can lead to pinhole leaks, while external contamination from dust and mud can reduce cooling efficiency. Symptoms of a failing oil cooler include:

• Hydraulic fluid overheating during extended use
  
• Visible oil seepage or wet spots near the cooler core
  
• Reduced hydraulic performance or sluggish controls
  
• Frequent high-temperature warnings on the dash
  

In one case, an operator noticed hydraulic oil spraying from the cooler core after a pressure spike. The machine had been working in dusty conditions, and the cooler fins were partially clogged, causing localized overheating and eventual rupture.
Replacement Options and Compatibility
The OEM oil cooler for the S175 is a specific part with a unique footprint and port configuration. However, several aftermarket suppliers offer direct-fit replacements, often at a lower cost. When sourcing a replacement, consider:

• Core dimensions: Match height, width, and depth to ensure proper fitment
  
• Port size and thread type: Typically SAE or NPT; verify before ordering
  
• Mounting brackets: Some aftermarket units require slight modification or reuse of original hardware
  
• Cooling capacity: Ensure the BTU/hr rating meets or exceeds OEM specifications
  

Some operators have successfully adapted coolers from other Bobcat models like the S185 or S150, provided the hydraulic flow rates and mounting points align. Others have installed universal stacked plate coolers with custom brackets and hose fittings.
Installation Tips and Best Practices

• Flush the hydraulic system before installing the new cooler to remove debris and prevent contamination
  
• Inspect and clean the radiator and fan shroud to ensure unobstructed airflow
  
• Use thread sealant or O-rings on fittings to prevent leaks
  
• Secure all hoses with clamps or crimped fittings rated for hydraulic pressure
  
• Test the system under load after installation and monitor for leaks or temperature spikes
  

Preventive Maintenance Recommendations

• Blow out cooler fins weekly using compressed air, especially in dusty environments
  
• Check for vibration or loose mounts that could stress the cooler core
  
• Monitor hydraulic fluid condition and change filters at recommended intervals
  
• Install a screen or debris guard in front of the cooler if working in brush or mulch
  

Conclusion
Replacing the oil cooler on a Bobcat S175 is a straightforward but critical repair that restores hydraulic performance and prevents costly damage. With proper sourcing, careful installation, and routine maintenance, operators can extend the life of both the cooler and the machine’s entire hydraulic system. Whether using OEM or aftermarket parts, attention to detail ensures the S175 stays productive and reliable in the field.