Bobcat 773G Coolant Gurgling and Cooling System Diagnostics

[MikePhua]

The Bobcat 773G and Its Engine Cooling Architecture
The Bobcat 773G skid steer loader was introduced as part of Bobcat’s G-series lineup in the early 2000s, designed for compact performance in construction, landscaping, and agricultural tasks. With a rated operating capacity of 1,750 lbs and a liquid-cooled Kubota V2203 diesel engine producing approximately 46 horsepower, the 773G became a popular choice for contractors needing maneuverability and reliability in tight spaces.
Bobcat Company, founded in North Dakota in 1947, has long been a leader in compact equipment innovation. The 773G’s cooling system is a closed-loop design featuring a radiator, thermostat, water pump, overflow reservoir, and a network of hoses. This system is engineered to maintain optimal engine temperature under varying loads and ambient conditions. However, symptoms like gurgling coolant often indicate underlying issues that require prompt attention.
Terminology Clarification

• Gurgling coolant: Audible bubbling or sloshing sounds from the radiator or reservoir, often caused by air pockets or boiling fluid.
  
• Closed-loop cooling system: A sealed system where coolant circulates continuously between the engine and radiator.
  
• Thermostat: A temperature-sensitive valve that regulates coolant flow based on engine temperature.
  
• Head gasket: A seal between the engine block and cylinder head that prevents coolant and combustion gases from mixing.
  

Common Causes of Coolant Gurgling
Gurgling sounds in the cooling system typically point to one or more of the following issues:

• Air trapped in the system after coolant replacement or leak
  
• Failing thermostat causing uneven coolant flow
  
• Weak radiator cap unable to maintain proper pressure
  
• Internal combustion gas leakage due to head gasket failure
  
• Partially blocked radiator or coolant passages reducing flow
  

A technician in Alberta encountered gurgling in a 773G after replacing the water pump. The issue persisted until the system was properly bled and the thermostat was replaced with an OEM-rated unit. The gurgling stopped, and coolant temperatures stabilized.
Diagnostic Strategy and Inspection Points
To identify the root cause:

• Check coolant level in the reservoir and radiator when cold
  
• Inspect for leaks around hoses, clamps, and the water pump
  
• Test radiator cap pressure rating (typically 13–16 psi for the 773G)
  
• Observe coolant flow through the radiator with the cap off during warm-up
  
• Use a combustion gas tester to detect exhaust gases in the coolant
  
• Monitor engine temperature with an infrared thermometer or onboard gauge
  

Recommended tools:

• Cooling system pressure tester
  
• Combustion leak detection kit
  
• Torque wrench for cap and housing bolts
  
• UV dye and blacklight for leak tracing
  

A contractor in Georgia used a combustion gas tester and confirmed head gasket failure in his 773G. After replacing the gasket and flushing the system, the gurgling ceased and the machine returned to full duty.
Bleeding the Cooling System and Restoring Flow
Air pockets are a frequent cause of gurgling and overheating. To bleed the system:

• Park the machine on level ground and allow the engine to cool
  
• Remove the radiator cap and fill with coolant to the neck
  
• Start the engine and let it idle with the cap off
  
• Observe for air bubbles and top off as needed
  
• Run the engine until the thermostat opens and coolant circulates
  
• Replace the cap and monitor reservoir level after shutdown
  

Tips:

• Use a funnel with a spill-free adapter to reduce mess
  
• Squeeze upper radiator hose gently to help release trapped air
  
• Avoid overfilling the reservoir, which can cause overflow during expansion
  
• Use premixed coolant or distilled water to prevent mineral buildup
  

A fleet manager in British Columbia added a bleeder valve to the upper radiator hose of his 773G units, simplifying air removal and reducing service time.
Preventive Maintenance and Long-Term Reliability
To prevent future coolant issues:

• Replace coolant every 2,000 hours or as recommended
  
• Inspect hoses and clamps quarterly for wear or looseness
  
• Replace the thermostat every 1,000 hours or during major service
  
• Flush the radiator annually to remove sediment and scale
  
• Use only manufacturer-approved coolant types and mixtures
  

Operator tips:

• Let the engine idle briefly before shutdown to stabilize temperature
  
• Report any coolant loss or temperature spikes immediately
  
• Avoid operating with low coolant levels, which can cause cavitation
  
• Keep radiator fins clean and free of debris for optimal airflow
  

A crew in Texas implemented a cooling system checklist as part of their daily walkaround. This helped catch early leaks and reduced overheating incidents by 80% over one season.
Conclusion
Gurgling coolant in the Bobcat 773G is often a symptom of air intrusion, pressure imbalance, or internal leakage. With structured diagnostics, proper bleeding procedures, and disciplined maintenance, these issues can be resolved before they lead to engine damage or downtime. The 773G’s compact design rewards proactive care, and its cooling system—though simple—requires precision to operate reliably under load. For technicians and operators alike, coolant clarity is a key to keeping this versatile machine productive and protected.