Essential Fluids for the CAT 307B Excavator: Types, Capacities, and Best Practices

[MikePhua]

Engine and Fuel System Fluids

• Fuel Tank: Capacity ~35.7 gal (135 L)
  
• Engine Oil (Crankcase): Approximately 1.9–2 gal (7–7.2 L)
  
• Cooling System: Holds around 4 gal (15 L)
  

Final Drives and Swing Gear

• Swing Drive (each side): ~0.4 gal (1.5 L)
  
• Final Drive (each side): ~0.45–0.5 gal (1.7–2 L)
  

Hydraulic System Capacities

• Total Hydraulic System (including tank): ~24.8–25 gal (94 L)
  
• Hydraulic Tank Only: ~15 gal (57 L)
  

Hydraulic Pressures & Flow Rates

• Maximum Travel Pressure: ~4,550 psi
  
• Maximum Swing Pressure: ~3,980 psi
  
• Pilot System:
  • Flow: ~4.9 gpm (19 L/min)
    
  • Pressure: ~500 psi
    
• Implement (blade) Circuit:
  • Flow: ~9 gpm
    
  • Max Pressure: ~2,990 psi
    

Terminology & Fluid Types

• BF‑2 Hydraulic Oil: A Cat-approved biodegradable hydraulic fluid ideal for environmentally sensitive applications—always verify machine compatibility first.
  
• Cat HYDO: The standard hydraulic oil for Caterpillar machines, available in SAE 10W or 30, formulated to maximize component life.
  
• SAE 10W Hydraulic Oil: Widely used across Cat excavators, offering reliable performance across temperature ranges.
  
• Diesel Engine Oil (15W‑40): Recommended as a secondary option for hydraulic systems when HYDO is unavailable.
  

Why Fluid Selection Matters
Hydraulic fluid does far more than just transfer power. It also:

• Maintains non-compressibility for consistent responsiveness
  
• Provides thermal and film lubrication stability
  
• Protects components from corrosion, wear, and air entrainment
  
• Supports filterability and cleanliness essential for machine health
  

Using improper fluids can lead to accelerated wear, valve sticking, efficiency loss, or even catastrophic failures.

Real-World Anecdote
A rental contractor in cold-weather Canada nearly froze a jobsite when the CAT 307B began digging sluggishly at dawn. The culprit? Thin, low-viscosity hydraulic fluid that couldn’t maintain pressure in frigid temps. After flushing and refilling with SAE 10W HYDO recommended by the manual, the excavator perked right up—fluid responsiveness returned, hydraulic performance normalized, and the job no longer risked slipping behind schedule.

Summary Table (As Lists)
Capacities–Fluid Type

• Fuel Tank: 35.7 gal (135 L)
  
• Engine Oil: 1.9–2 gal (7–7.2 L)
  
• Cooling System: 4 gal (15 L)
  
• Swing Drive (each): 0.4 gal (1.5 L)
  
• Final Drive (each): 0.45–0.5 gal (1.7–2 L)
  
• Hydraulic System (total): 24.8–25 gal (94 L)
  
• Hydraulic Tank Only: 15 gal (57 L)
  

Hydraulic Pressure & Flow

• Travel Pressure: ~4,550 psi
  
• Swing Pressure: ~3,980 psi
  
• Pilot System Flow/Pressure: ~4.9 gpm / ~500 psi
  
• Blade Circuit Flow/Pressure: ~9 gpm / ~2,990 psi
  

Choosing the right fluids—from engine oil to hydraulic oil—matters more than many operators realize. Proper maintenance not only ensures peak performance but also extends the lifespan of your CAT 307B. If you'd like help selecting condition-based fluid change intervals or compatible alternatives, just let me know!