White Smoke and Fuel Rich Running in the CAT 259B

[MikePhua]

The CAT 259B and Its Compact Track Loader Lineage
The Caterpillar 259B is part of CAT’s B-series compact track loaders, designed for high-performance operation in confined spaces. Introduced in the mid-2000s, the 259B featured a turbocharged diesel engine, pilot joystick controls, and a suspended undercarriage system for improved traction and operator comfort. With an operating weight of around 8,000 pounds and a rated operating capacity near 2,900 pounds, it was built for grading, lifting, and material handling in construction and landscaping.
Caterpillar Inc., founded in 1925, has long dominated the compact equipment market. The 259B was a continuation of CAT’s push into rubber-tracked loaders, offering better flotation and reduced ground disturbance compared to wheeled skid steers. Thousands of units were sold across North America, and many remain in service today.
Intermittent White Smoke and Engine Choking
A recurring issue with the 259B involves periodic white smoke emissions accompanied by rich running and engine choking. The problem tends to appear every few weeks, often during routine operation such as topsoil removal or material relocation. The machine runs normally most of the time but suddenly begins emitting thick white smoke, sounding fuel-rich, and eventually stalls.
Key symptoms include:

• White smoke with a distinct fuel odor
  
• No coolant loss or overheating
  
• Misfire-like engine behavior
  
• Temporary recovery after priming or fuel system bleeding
  

These signs point to incomplete combustion, likely caused by air intrusion, injector malfunction, or fuel delivery inconsistency.
Terminology and Diagnostic Concepts
- White Smoke: Typically indicates unburned fuel or coolant vapor. In this case, the smell confirms it’s fuel-related.
- Running Rich: A condition where excess fuel enters the combustion chamber, leading to poor combustion and smoke.
- Fuel Priming: Manually pressurizing the fuel system to remove air and restore flow.
- Injector Testing: Bench testing injectors for spray pattern, flow rate, and leakage.
- Filter Head Assembly: The housing that holds the fuel filter and connects to the fuel lines. Internal blockages here can restrict flow.
Root Causes and Field Observations
One operator noted that switching from a third-party fuel filter to a genuine CAT filter caused the machine to run poorly for several minutes, blowing white smoke and sounding “super fat.” Upon priming the fuel pump, he heard air escaping from the pump housing above the filter. Loosening the pump revealed a hiss, after which the machine ran normally.
This suggests air intrusion at the filter head or pump seal. If air enters the system, it disrupts injector timing and causes unburned fuel to exit through the exhaust. The issue may be exacerbated by cold weather, as another operator in Alaska reported similar symptoms worsening in low temperatures.
Turbocharger Considerations
Some technicians suspect the turbocharger wastegate may be sticking open, reducing boost pressure and causing incomplete combustion. While the 259B’s turbo configuration varies by production year, a stuck wastegate would result in low air volume, rich fuel mixture, and white smoke.
To test the turbo:

• Inspect actuator movement during throttle changes
  
• Check boost pressure with a gauge at full load
  
• Listen for whistling or fluttering sounds indicating vane or bearing wear
  

If the turbo is functioning normally, focus should return to the fuel system.
Recommendations for Repair and Prevention
To resolve intermittent white smoke and rich running:

• Replace fuel filters with OEM-grade units
  
• Disassemble and clean the filter head assembly thoroughly
  
• Inspect fuel lines for cracks, loose clamps, or dry rot
  
• Bench test injectors for spray pattern and leakage
  
• Prime the fuel system after filter changes or line repairs
  
• Monitor turbo boost pressure and actuator function
  

If the issue persists, consider replacing the fuel pump or filter head entirely. Some operators report success after switching to a newer-style filter head with improved sealing and flow characteristics.
Field Anecdotes and Practical Advice
One technician in Indiana noted that his 259B ran poorly after switching to a non-CAT filter. After returning to the OEM filter and priming the system, the machine ran smoothly. He emphasized the importance of sealing integrity at the pump and filter head.
Another operator in Pennsylvania found that cleaning the filter head passages resolved a similar issue. He recommended disassembling the entire head and using compressed air to clear internal cavities, especially after fuel contamination or long storage periods.
Conclusion
White smoke and fuel-rich running in the CAT 259B are often symptoms of air intrusion or fuel delivery inconsistency. While injectors and turbochargers may play a role, the filter head and pump seals are frequent culprits. With careful inspection, proper priming, and use of OEM components, operators can restore performance and eliminate the guesswork. In compact loaders, combustion precision is everything—and even a whisper of air can cloud the job.