Identifying the Year of a Caterpillar D4 Dozer

[MikePhua]

The D4 Series and Its Historical Significance
The Caterpillar D4 dozer has been a cornerstone of mid-size earthmoving since its introduction in the 1930s. Originally derived from the Caterpillar Thirty, the D4 evolved through multiple generations, each marked by changes in engine configuration, undercarriage design, and operator ergonomics. The model designation “D4” remained consistent, but the internal codes and serial number prefixes changed with each production phase.
By the 1950s, the D4 had become a staple in agriculture, forestry, and construction. Its compact footprint and reliable diesel engine made it ideal for grading, clearing, and light dozing. Caterpillar continued refining the D4 through the 1970s and 1980s, introducing turbocharged variants, power shift transmissions, and hydraulic blade controls.
Serial Number Prefixes and Year Identification
Caterpillar uses a serial number system that includes a three-character prefix followed by a five-digit sequence. This format helps identify the model, configuration, and year of manufacture.
Examples of D4 serial prefixes:

• 2T: Early D4 models from the 1940s
  
• 7U: D4 models from the 1950s
  
• 2T and 5T: Diesel versions with direct start or pony motor
  
• 80J: D4C series from the 1980s
  
• 6YJ: D4H series from the late 1980s to early 1990s
  
• 9DB: D4E series
  
• 1FW: D4G series
  
• CAT00D4K: D4K series from the 2000s onward
  

To determine the year of a specific D4, locate the serial number plate—typically found on the rear of the machine near the transmission case or on the left side of the frame. Cross-reference the prefix and sequence ID with Caterpillar’s official serial number tables or consult a dealer database.
In one case from Montana, a contractor discovered his D4 had a 7U prefix and a sequence number in the 20,000 range. This placed the machine’s build year around 1956. He later confirmed this by matching casting dates on the engine block and transmission housing.
Engine Variants and Configuration Clues
Different D4 generations used distinct engines:

• D4 2T: Caterpillar D4400 diesel, 4-cylinder, 40 hp
  
• D4 7U: Caterpillar D315 diesel, 4-cylinder, 50 hp
  
• D4C: Caterpillar 3304 engine, 75 hp
  
• D4H: Caterpillar 3304 turbocharged, 90 hp
  
• D4G/D4K: Caterpillar C4.4 ACERT, Tier 3 and Tier 4 compliant, 92–100 hp
  

Engine casting numbers and injector pump types can help narrow down the year. For example, the D315 engine used in the 7U series has a distinctive side-mounted pony motor for cold starts, phased out in later models with direct electric start.
A technician in Alberta identified a D4H by its turbocharger and side-mounted oil cooler, confirming it was built in 1991. He used the engine’s serial number and casting date to verify parts compatibility.
Undercarriage and Blade Configuration Clues
The undercarriage design also evolved:

• Early D4s: Dry chain tracks, manual tensioning, cable blade lift
  
• Mid-series: Sealed and lubricated tracks, hydraulic blade lift
  
• D4H/D4G: Oscillating track frames, power angle tilt blades
  
• D4K: Integrated joystick blade control, electronic monitoring
  

Blade types include:

• Straight blade (S-blade): Simple grading
  
• Angle blade (A-blade): Versatile for pushing and windrowing
  
• Power angle tilt (PAT blade): Hydraulic control for slope work
  

In one restoration project in Oregon, a collector rebuilt a 7U D4 with a cable-operated S-blade. He fabricated new sheaves and installed a modern winch system, preserving the machine’s vintage look while improving usability.
Documentation and Historical Resources
To confirm a D4’s year, use:

• Serial number tables from Caterpillar archives
  
• Casting dates on engine block, transmission, and final drives
  
• Parts manuals and service bulletins
  
• Dealer lookup tools and legacy equipment registries
  

Some enthusiasts maintain private databases of serial numbers and build years. Others rely on forums and collector networks to trace obscure models.
A retired operator in Pennsylvania compiled a handwritten log of every D4 he worked on from 1962 to 1995, noting serial numbers, blade types, and engine quirks. His records helped a local museum identify a 1954 D4 used in flood recovery.
Conclusion
Identifying the year of a Caterpillar D4 dozer requires careful examination of serial numbers, engine components, and undercarriage features. With dozens of variants spanning nearly a century, each D4 tells a story of engineering evolution and field-tested resilience. Whether restoring a vintage 7U or maintaining a Tier 4 D4K, understanding its lineage ensures accurate parts sourcing and preserves the legacy of one of Caterpillar’s most enduring machines.