Fuel Prime Loss and Cold Start Challenges on the John Deere 650J Dozer

[MikePhua]

The 650J and Its Fuel Delivery System
The John Deere 650J is a mid-size crawler dozer introduced in the early 2000s as part of Deere’s J-series lineup. Designed for grading, site prep, and forestry work, the 650J features a Tier 2 diesel engine, hydrostatic transmission, and electronically controlled fuel delivery. Deere’s engineering emphasis on modular serviceability and operator comfort made the 650J a popular choice among contractors and municipalities.
Its fuel system includes a lift pump, dual fuel filters, a hand priming pump, and electronically actuated injectors. While generally reliable, the system can lose prime under certain conditions—especially after filter service, prolonged idle periods, or when air enters the lines due to seal degradation.
Terminology Annotation
- Lift Pump: A low-pressure pump that draws fuel from the tank and supplies it to the injection system.
- Hand Priming Pump: A manual pump used to purge air from the fuel system and restore pressure after maintenance.
- Bleed Port: A valve or fitting used to release trapped air from the fuel lines or filters.
- Gas Rag Start: An improvised method of starting a diesel engine by introducing a small amount of volatile vapor at the air intake to aid combustion.
Symptoms and Field Diagnosis
Operators may encounter the following sequence:

• After draining water from the rear fuel filter, the engine fails to start
  
• Hand priming pump feels firm for a few strokes, then softens
  
• Fuel flows freely from the front bleed port when opened
  
• Engine cranks but does not fire until gas rag is applied to air intake
  
• After running, the engine starts again briefly, then stalls and refuses to restart without assistance
  

This behavior suggests intermittent fuel delivery, likely caused by air intrusion or a failing lift pump. The fact that fuel reaches the injector lines confirms that the system is not completely dry, but pressure may be insufficient for proper atomization.
A Story from the Timberline
In South Carolina, a forestry operator servicing his 650J noticed that after draining the water separator, the machine refused to start. He bled the filters, confirmed fuel at the injectors, and resorted to a gas rag to get it running. The dozer performed well during operation but stalled after sitting for a few hours. Suspecting a weak lift pump, he checked the engine oil dipstick and found traces of diesel—indicating internal leakage. Replacing the lift pump resolved the issue, and the machine returned to reliable cold starts.
Lift Pump Failure and Internal Leakage
A common cause of prime loss is a compromised lift pump. These pumps can leak internally, allowing fuel to drain back into the tank or seep into the crankcase. Symptoms include:

• Diesel odor in engine oil
  
• Rising oil level without coolant contamination
  
• Soft priming pump after sitting overnight
  
• Difficulty maintaining fuel pressure at idle
  

To confirm, remove the lift pump and inspect for diaphragm damage or fuel residue in the crankcase. Replacement pumps are readily available and typically cost between $80 and $150 depending on brand and supplier.
Recommendations for Preventing Prime Loss
To maintain consistent fuel delivery:

• Replace both fuel filters every 500 hours or annually
  
• Use OEM or high-quality aftermarket filters with proper sealing
  
• Inspect fuel lines for cracks, loose clamps, or degraded rubber
  
• Test lift pump pressure with a gauge (should exceed 5 psi at idle)
  
• Bleed system thoroughly after filter changes using both bleed ports
  
• Avoid draining filters unless water contamination is confirmed
  

If the machine is stored for extended periods, consider installing a check valve in the fuel line to prevent backflow. For machines operating in cold climates, use winter-grade diesel and keep the tank full to reduce condensation.
Clarifying Terminology in Troubleshooting
In diagnostic discussions, the term “won’t crank” is often misused to mean “won’t start.” Technically, “crank” refers to the engine turning over via the starter. If the starter engages but the engine fails to fire, the correct term is “won’t start.” Clear terminology helps avoid confusion when communicating with technicians or sourcing support.
Conclusion
Fuel prime loss in the John Deere 650J dozer is typically caused by air intrusion, filter issues, or lift pump failure. With methodical inspection and attention to pressure behavior, operators can restore reliable starting and prevent downtime. Understanding the nuances of the fuel system—especially the role of the lift pump and bleed ports—is essential for maintaining performance in demanding field conditions. For legacy machines like the 650J, precision in maintenance and clarity in troubleshooting remain the keys to long-term reliability.