Diagnosing a No-Start Condition on a CAT 953 Track Loader

[MikePhua]

The CAT 953 and Its Mechanical Heritage
The Caterpillar 953 track loader has long been a staple in earthmoving operations, blending the versatility of a loader with the traction of a dozer. Introduced in the early 1980s, the 953 series evolved through multiple generations—A, B, C, and beyond—each improving on hydraulic efficiency, operator comfort, and emissions compliance. Powered by the CAT 3204 engine in earlier models, the 953 offered a robust mechanical platform with a reputation for reliability in quarrying, demolition, and site prep.
By the late 1990s, Caterpillar had sold tens of thousands of 953 units globally, with strong adoption in North America and Latin America. The 3204 engine, a naturally aspirated four-cylinder diesel, was known for its simplicity and ease of service, but like all mechanical systems, it could develop quirks—especially after long periods of inactivity.
Initial Symptoms and Context
In one case, a 953 loader equipped with a 3204 engine and pull-type shutdown system had been sitting idle for approximately a year. Prior to storage, it ran reliably—even after extended downtime. Upon attempted restart, the engine turned over rapidly but failed to fire. Initially, black smoke was observed during cranking, suggesting fuel delivery and compression were present. However, subsequent attempts produced no smoke at all.
This shift in behavior pointed toward a fuel system fault, possibly compounded by stale diesel, air intrusion, or electrical degradation.
Fuel System Checks and Common Oversights
Diesel engines rely on clean, pressurized fuel and air to ignite. After prolonged storage, several issues can arise:

• Water accumulation in the fuel tank due to condensation
  
• Microbial growth in diesel, forming sludge and clogging filters
  
• Air leaks in suction lines or fittings
  
• Stuck injection pump plungers or governor linkages
  

Recommended steps include:

• Draining water from the fuel tank and filters using built-in drain valves
  
• Replacing primary and secondary fuel filters
  
• Inspecting the hand priming pump for leaks or failure
  
• Bleeding the fuel system at injector lines to confirm delivery
  
• Verifying fuel shutoff solenoid or mechanical linkage operation
  

In this case, the fuel had been checked and water drained, but the absence of smoke during cranking suggested that fuel was no longer reaching the cylinders.
Air Intake and Combustion Clues
Air restriction can also prevent combustion. Mice and insects often nest in air filter housings during storage, blocking airflow. A quick inspection of the air filter and intake ducting is essential. If the engine turns over fast but produces no exhaust smoke, it may not be receiving fuel or air—or both.
The presence of black smoke during initial cranking indicated incomplete combustion, likely due to poor atomization or low cylinder temperature. As attempts continued, the smoke disappeared, suggesting fuel starvation or injector failure.
Electrical and Battery Considerations
While the 953’s early models are largely mechanical, electrical components still play a role in starting. Weak batteries may spin the engine but fail to energize solenoids or provide sufficient voltage to the starter under load. After sitting for a year, batteries should be replaced—not just recharged.
Additional checks:

• Clean and tighten all battery terminals
  
• Inspect ground straps for corrosion
  
• Test voltage drop during cranking
  
• Confirm starter solenoid engagement
  

In one documented case, a loader exhibited similar symptoms due to a corroded ground strap hidden beneath the cab. Once replaced, the machine fired immediately.
Serial Number Confusion and Parts Ordering Risks
The serial number provided—initially misread as 44200153—was later corrected to 44Z00153, confirming the machine as a 953 with a 3204 engine. This highlights the importance of accurate serial identification when ordering parts. A single digit error can result in receiving components for an entirely different machine—such as a 994F haul truck, whose bucket cylinder weighs over 2,000 pounds.
Dealers rely on serial numbers to match arrangement numbers, engine configurations, and transmission types. Always verify the serial plate and cross-reference with the manufacturer’s SIS (Service Information System) before placing orders.
Injection Pump and Mechanical Shutdown Linkage
The 953 uses a mechanical fuel injection pump with a pull-type shutdown lever. If the lever or governor linkage is stuck, the pump may remain in the “off” position despite cranking. Lubricating the linkage and manually cycling the lever can restore movement.
If the pump plungers are seized due to varnish or corrosion, professional rebuilding may be required. A master injection pump rebuilder once noted that sitting idle with untreated diesel can cause internal scoring and binding, especially in humid climates.
A Story from the Iron Ore Fields of Chile
One technician recalled assembling the first 994F haul truck in Chile, where a misread serial number led to a parts mix-up. Instead of receiving filters, the dealer shipped a dozen dump bodies—each weighing over 30 tons. The error stemmed from a transposed digit in the stock order. This anecdote underscores the importance of precision in serial identification, especially when dealing with legacy equipment.
Conclusion
A CAT 953 loader that turns over but won’t start after long-term storage likely suffers from fuel system degradation, air restriction, or electrical weakness. By methodically inspecting fuel delivery, air intake, battery integrity, and mechanical linkages, operators can isolate the fault and restore function. With its rugged 3204 engine and straightforward design, the 953 remains a serviceable workhorse—provided its systems are treated with care and its serial numbers read correctly.