Comparing the Caterpillar D6H and D6H Series II Dozers

[MikePhua]

The D6H and Its Role in Earthmoving History
The Caterpillar D6H was introduced in the mid-1980s as part of Cat’s evolution of the D6 series, which dates back to the 1940s. Designed for grading, pushing, and site preparation, the D6H featured a torque converter drive, elevated sprocket undercarriage, and a 3306 turbocharged diesel engine producing around 165 horsepower. Its elevated sprocket design improved final drive protection and track life, while the torque converter allowed smoother operation in variable terrain.
The D6H became a favorite among contractors for its balance of power, maneuverability, and serviceability. It was widely used in road building, forestry, and mining reclamation. By the early 1990s, Caterpillar introduced the D6H Series II, refining the platform with improved hydraulics, electronics, and operator comfort.
Key Differences Between D6H and D6H Series II
While both machines share the same basic frame and undercarriage layout, several upgrades distinguish the Series II:

• Hydraulic System
  The Series II features a load-sensing hydraulic system with improved response and efficiency. Blade control is smoother, especially during fine grading.
  
• Operator Station
  Cab insulation, seat suspension, and control ergonomics were enhanced. The Series II offers better visibility and reduced operator fatigue.
  
• Electrical System
  Wiring harnesses were upgraded for reliability, and diagnostic connectors were added to simplify troubleshooting.
  
• Cooling Package
  Improved radiator and fan design reduced operating temperatures, especially in high-load applications.
  
• Transmission Controls
  The Series II introduced electronic modulation for smoother gear shifts and better torque management.
  

These refinements made the Series II more productive and comfortable, especially for long shifts and precision work.
Engine and Powertrain Comparison
Both models use the Cat 3306 engine, a six-cylinder turbocharged diesel known for durability and ease of service. However, the Series II benefits from refined fuel mapping and better cold-start characteristics.
Torque converter and transmission components are largely interchangeable, but the Series II may feature updated clutch packs and valve bodies. Final drives and track frames remain consistent, allowing parts interchangeability in most cases.
Undercarriage and Blade Options
The D6H and D6H Series II support multiple blade configurations:

• Straight blade (S-blade) for fine grading
  
• Universal blade (U-blade) for bulk pushing
  
• Semi-U blade for general-purpose work
  
• Angle blade for ditching and slope work
  

Track options include standard and wide-gauge configurations, with optional swamp pads for soft terrain. The elevated sprocket design reduces debris buildup and improves component life.
Maintenance and Parts Availability
Due to their popularity, both models enjoy strong aftermarket support. Key maintenance tips include:

• Replace final drive oil every 500 hours
  
• Inspect track tension weekly and adjust as needed
  
• Grease blade pivot points daily
  
• Monitor torque converter temperature during heavy pushing
  
• Use OEM filters and fluids for optimal longevity
  

Some operators retrofit LED lighting, GPS blade control, and upgraded seats to older D6H units, bringing them closer to Series II comfort and capability.
A Story from the Field
In 2016, a contractor in British Columbia operated both a D6H and a Series II on a mountain road project. The original D6H handled bulk pushing and slope shaping, while the Series II performed finish grading. Operators noted that the Series II’s blade response and cab comfort made it ideal for precision work, while the older D6H remained a reliable brute for moving volume. Both machines ran side by side for three months without major issues, demonstrating the enduring value of the platform.
Conclusion
The Caterpillar D6H and D6H Series II represent two generations of a proven earthmoving platform. While the Series II offers refinements in hydraulics, comfort, and control, the original D6H remains a workhorse with unmatched mechanical simplicity. For contractors, the choice depends on application, budget, and operator preference. In the world of dozers, legacy and innovation often share the same tracks—and when the blade drops, both machines prove their worth in dirt, rock, and time.