Hydraulic Cooling Fan Sticking Issues on the Bobcat S510

[MikePhua]

The S510 and Its Cooling System Design
The Bobcat S510 skid-steer loader is part of Bobcat’s M-series, introduced in the early 2010s to improve operator comfort, hydraulic performance, and serviceability. With a rated operating capacity of 1,790 lbs and powered by a 61-horsepower Tier 4 diesel engine, the S510 is widely used in landscaping, construction, and agricultural applications. One of its key features is the hydraulic-driven cooling fan, designed to modulate speed based on engine temperature and hydraulic load.
Unlike belt-driven fans, the hydraulic fan system in the S510 offers variable speed control, reducing noise and improving fuel efficiency. However, this system introduces complexity, and over time, some machines develop issues where the fan sticks or fails to modulate properly.
Terminology Annotation

• Hydraulic Cooling Fan: A fan powered by hydraulic fluid pressure, controlled by a proportional valve or solenoid.
  
• Fan Sticking: A condition where the fan remains engaged or fails to respond to control signals, often due to mechanical or electrical faults.
  
• Proportional Valve: A valve that adjusts flow based on electrical input, used to control fan speed in response to temperature.
  
• Thermal Sensor: A device that monitors coolant or hydraulic oil temperature and signals the fan control system.
  

Symptoms and Field Observations
Operators have reported several symptoms related to fan sticking:

• Fan runs continuously at high speed, even when the engine is cold
  
• Fan fails to engage during high-load operations, leading to overheating
  
• Intermittent fan response, with erratic speed changes
  
• Audible hydraulic whine or resistance when fan attempts to engage
  

In one excavation crew in Arizona, an S510 began overheating during trenching work. The fan was visually spinning, but at low speed despite high coolant temperatures. After inspection, the technician found the proportional valve stuck due to contamination in the hydraulic fluid.
Root Causes and Diagnostic Strategy
Fan sticking issues typically stem from a combination of hydraulic contamination, electrical faults, and mechanical wear. A structured diagnostic approach includes:
Hydraulic system:

• Check hydraulic fluid condition for contamination or degradation
  
• Inspect fan motor for signs of internal leakage or bearing wear
  
• Test proportional valve for smooth operation and response to voltage input
  

Electrical system:

• Verify thermal sensor output using a multimeter
  
• Inspect wiring harness for damage, corrosion, or loose connectors
  
• Test fan control module for proper signal modulation
  

Mechanical system:

• Ensure fan blades are free of debris and rotate without resistance
  
• Check mounting bolts and brackets for misalignment or vibration damage
  

In a fleet in Ontario, a technician discovered that a fan motor had seized due to bearing failure. The motor was replaced, and the hydraulic fluid flushed, restoring normal operation.
Repair Solutions and Preventive Measures
To resolve fan sticking and prevent recurrence:

• Replace hydraulic fluid and filter every 500 hours or annually
  
• Clean or replace the proportional valve if sticking is detected
  
• Upgrade thermal sensors to more responsive units if lag is observed
  
• Install a fan override switch for manual control during diagnostics
  

Suggested specs:

• Hydraulic fluid: ISO VG 46 or Bobcat All Season Hydraulic Fluid
  
• Fan motor operating pressure: 2,000–2,500 psi
  
• Proportional valve voltage range: 0–12V DC
  
• Thermal sensor resistance: varies by temperature, typically 1–3 kΩ
  

In one rental fleet in Texas, adding a fan status indicator light helped operators identify when the fan was active, reducing overheating incidents by 60%.
Operational Tips and Seasonal Adjustments
To optimize fan performance:

• Avoid prolonged idling in hot weather without airflow
  
• Clean radiator fins and fan blades weekly during dusty operations
  
• Monitor coolant and hydraulic temperatures during high-load tasks
  
• Use engine preheat in winter to reduce cold-start hydraulic strain
  

In Wisconsin, a contractor installed a cab-mounted temperature gauge linked to the hydraulic oil sensor. This allowed real-time monitoring and early intervention when temperatures rose unexpectedly.
Final Thoughts
The hydraulic cooling fan on the Bobcat S510 is a sophisticated system that enhances efficiency and noise control. However, its performance depends on clean fluid, responsive sensors, and precise valve operation. With regular maintenance and thoughtful upgrades, operators can ensure reliable cooling and avoid costly downtime.
In the quiet spin of a fan and the steady hum of hydraulics, the S510 keeps its cool—proving that smart systems still need smart care.