Bobcat T86 Super-Flow Hydraulic System Overheating Diagnostic

Symptoms

• Hydraulic oil temperature warning light on the Deluxe Display
• Engine power derate and drop in auxiliary flow rate
• Excessive noise from hydraulic pumps (cavitation warning)
• Hydraulic oil aerated or foaming in the reservoir sight glass

Possible Causes

• Plugged hydraulic oil cooler fins due to debris ingestion
• Reversing cooling fan clutch or solenoid valve failure
• Failing hydraulic oil thermal bypass valve stuck in bypass mode
• Excessive internal leakage (slippage) in the High-Flow/Super-Flow auxiliary pump

Diagnostic Procedure

1. 1
   Perform Visual inspection and Airway Check

   Inspect the cooling pack behind the rear door. Check for packed debris, leaf matter, and dust within the radiator, charge air cooler, and hydraulic oil cooler fins. Blow out standard and Super-Flow coolers with low-pressure compressed air or water from inside out.
2. 2
   Test Cooling Fan Clutch Operation

   Connect Bobcat Service Analyzer. Access the hydraulic system control monitor. Manually command the reversible fan to maximum RPM. Measure active fan speed with a photo-tachometer and compare it to engine RPM. Verify the fan reverses direction on command.
3. 3
   Evaluate Thermal Bypass Valve Performance

   Use an infrared thermometer to monitor temperatures directly on the inlet and outlet of the thermal design bypass block. Under cold conditions, oil should bypass the cooler. Once oil reaches 140 degrees F (60 degrees C), verify a significant temperature drop at the cooler outlet, indicating the bypass valve has fully closed to direct flow through the cooler.
4. 4
   Conduct High-Pressure Flow Meter Test

   Install a high-pressure inline flow meter and load cell to the Super-Flow auxiliary quick couplers. Run engine at full throttle, actuate manual flow, and slowly restrict the flow meter to load the system to 4,000 PSI (275 bar). Check if the flow drops more than 10 percent from nominal specifications; excessive drop indicates pump volumetric wear.

Common Repairs

• Deep core thermal cleanout
• Replacement of hydraulic thermal bypass cartridge valve
• Replacement of electronically controlled hydraulic fan clutch assembly
• Auxiliary tandem tandem-pump replacement

Safety Precautions

• Never check hydraulic leaks with bare hands; use cardboard to search for high-pressure micro-leaks.
• Wait for machine and cooling jacket to cool down before pressure measurements.
• Wear high-temperature oil protective gloves and dynamic eye protection.

Required Tools

• Infrared temperature gun
• Digital photo-tachometer
• High-flow hydraulic test kit (flow meter/load cell)
• Bobcat Service Analyzer Laptop

Related Fault Codes

People Also Ask

• Why is my Bobcat T86 throwing fault code D7515-00?
• How do I test the hydraulic cooling fan speed on a Bobcat T86?
• What causes auxiliary hydraulic flow to drop during heavy use on Bobcat Super-Flow?
• How to troubleshoot Bobcat fault code E0085 cooling fan deviation?
• Why is the hydraulic fluid foaming in my Bobcat T86 reservoir?
• How do you diagnose a M0165 solenoid fault on a Bobcat loader?
• Is a Bobcat D34 engine derate linked to hydraulic oil temperature?

Related Guides

Suggested Follow-Up Guides

• Bobcat T86 Hydraulic Fan Clutch and Solenoid Replacement Guide
• Troubleshooting Bobcat D34 Engine Derate and Cooling System Failures
• Bobcat Super-Flow Auxiliary Hydraulic Valve Block Rebuild Manual
• Step-by-Step Hydraulic Pressure and Flow Testing for Bobcat T-Series Loaders
• Diagnosing Cavitation and Air Leaks in Bobcat Hydraulic Suction Lines

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