Bobcat T86 Reversible Cooling Fan System Failure

Symptoms

• No reversing cycle occurs during operation (standard auto-purge missing)
• Manual fan-reverse button of the dashboard panel flashes error signs
• Rapid build-up of wood fiber, leaves, or particulate on the outer door grate

Possible Causes

• Failed reversing valve control solenoid coil or broken electrical harness wire
• Mechanical binding of the directional blades or assembly frame
• Lack of sufficient pilot control charge pressure to shift the hydraulic motor directional valve spool

Diagnostic Procedure

1. 1
   Inspect Mechanical Assembly for Obstructions

   Verify fan spins freely by hand when engine is completely off. Inspect the fan motor blades, checking for cracks or deformation. Check the plastic fan shroud to ensure clear margins all around, with no signs of physical contact.
2. 2
   Measure Solenoid Coil Electrical Parameters

   Locate the hydraulically operated fan-motor manifold block. Locate the 12V reversing solenoid valve assembly. Unplug the connector and test spool coil resistance with a multimeter. A resistance reading of 6 to 10 Ohms is normal. A reading of infinity indicates an open internal coil circuit.
3. 3
   Verify Commanded Control Signal Voltage

   Connect a digital multimeter to the harness side plug of the solenoid. Initiate are manual override fan reverse cycle using the in-cab display. A solid transition from 0V to 12V during the command phase should be observed. If no voltage change occurs, trace the harness up to the cooling control relay.
4. 4
   Conduct Hydraulic Pressure Check at Fan Motor

   Install a 5,000 PSI hydraulic pressure gauge into the fan motor test port. Monitor hydraulic main loop pressure when cold vs working temperature. If system hydraulic pressure remains below minimum spec (typically 2,500-3,000 PSI under full speed demand), check for a faulty dynamic hydraulic control block or worn pump.

Common Repairs

• Replacing the reversing solenoid valve assembly coil
• Reconditioning/cleaning the fan motor valve block slide spool
• Installing a replacement hydraulic cooling fan motor assembly

Safety Precautions

• Never engage in diagnostics within the rear compartment while the engine is running.
• Secure hair, loose clothing, and dangling testing leads far away from spinning cooling fans.

Required Tools

• Multimeter with needle testing probes
• 5,000 PSI hydraulic pressure gauge
• Automotive clean-bore brush kit

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Related Guides

Suggested Follow-Up Guides

• Bobcat T86 Engine Harness Replacement & Pinout Guide
• How to Diagnose Bobcat D34 Hydraulic Fan Motor Control Valves
• Bobcat T86 Deluxe Instrument Panel Diagnostic Codes and Troubleshooting
• Bobcat Compact Track Loader Hydraulic Solenoid Coil Testing and Replacement

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