Cummins Diesel Engines: Complete Guide to 5.9L and 6.7L Powerhouses

Cummins Diesel Engines: Complete Guide to 5.9L and 6.7L Powerhouses

The Legendary Cummins Diesel Engine

Cummins diesel engines have earned a legendary reputation for durability, power, and longevity that's unmatched in the diesel world. Whether you drive a RAM 2500/3500, Nissan Titan XD, or commercial vehicle, when your Cummins needs replacement, understanding these powerhouses helps you make the right choice.

At Used Engines Store, we specialize in Cummins diesel engines and know what makes them capable of 500,000+ mile lifespans. Here's your complete guide to Cummins 5.9L and 6.7L diesel engines.

Cummins Engine Generations

5.9L Cummins (2003-2007) - The Legend

  • Power: 305-325 hp
  • Torque: 555-610 lb-ft
  • Known for: Legendary reliability, simplicity, 500,000+ mile lifespan
  • Common in: RAM 2500/3500 (2003-2007)
  • Common issues: Lift pump failures, injector issues (minor)
  • Why it's legendary: Pre-emissions simplicity, bulletproof design, highly sought after

6.7L Cummins (2007.5-2012) - First Generation

  • Power: 350-385 hp
  • Torque: 650-850 lb-ft
  • Known for: More power than 5.9L, still relatively simple
  • Common issues: DPF/EGR emissions complexity, grid heater failures

6.7L Cummins (2013-2018) - Second Generation

  • Power: 370-400 hp
  • Torque: 800-930 lb-ft
  • Known for: Improved emissions, better fuel economy
  • Common issues: CP4 fuel pump failures, DEF system issues

6.7L Cummins (2019-Present) - Third Generation

  • Power: 370-420 hp
  • Torque: 850-1,075 lb-ft
  • Known for: Massive torque, refined operation
  • Common issues: Too new to determine long-term issues

Why Cummins Engines Last 500,000+ Miles

The Cummins advantage:

1. Cast Iron Construction

  • Extremely durable block and cylinder heads
  • Handles extreme stress and heat
  • Can be rebuilt multiple times

2. Inline-6 Design

  • Inherently balanced (no vibration)
  • Even firing order
  • Less stress on components
  • Smooth operation

3. Conservative Factory Tuning

  • Built to handle much more power than stock
  • Massive safety margin
  • Can be tuned to 500+ hp reliably

4. Simple, Proven Design

  • Mechanical fuel injection (5.9L)
  • Common rail (6.7L) but still robust
  • Fewer complex systems than competitors

5. Commercial-Grade Durability

  • Designed for heavy-duty commercial use
  • Built for continuous operation
  • Extreme towing and hauling capability

Bottom line: A well-maintained Cummins can outlast multiple trucks. Many owners swap Cummins engines into newer trucks.

Common Cummins Problems (Maintenance Items)

5.9L Cummins Issues:

1. Lift Pump Failure

  • Problem: Factory lift pump fails, starving injection pump
  • Mileage: 100,000-150,000 miles
  • Symptoms: Hard starting, loss of power, surging
  • Solution: Aftermarket lift pump upgrade ($300-$600)
  • Impact: Can damage injection pump if ignored

2. Injector Failures

  • Problem: Injectors wear out over time
  • Mileage: 150,000-200,000 miles
  • Symptoms: Rough idle, black smoke, loss of power
  • Solution: Replace injectors ($1,500-$3,000 for all 6)

3. VP44 Injection Pump (1998.5-2002)

  • Problem: Electronic injection pump fails
  • Cause: Lift pump failure starves VP44
  • Solution: Replace VP44 ($1,200-$2,000) and lift pump

6.7L Cummins Issues:

1. DPF/EGR Emissions System

  • Problem: DPF clogs, EGR coolers fail
  • Symptoms: Reduced power, regen cycles, check engine light
  • Solution: DPF cleaning ($300-$600), EGR replacement ($800-$1,500)
  • Note: Some owners delete emissions (check local laws)

2. CP4 Fuel Pump Failure (2013-2018)

  • Problem: CP4 pump fails catastrophically, contaminating fuel system
  • Symptoms: Sudden loss of power, metal in fuel
  • Solution: Replace entire fuel system ($8,000-$12,000)
  • Prevention: CP3 conversion kit ($2,000-$3,000)

3. Grid Heater Failures

  • Problem: Grid heater elements break, get sucked into engine
  • Solution: Grid heater delete or upgrade ($200-$400)

4. Turbocharger Wear

  • Mileage: 200,000-300,000 miles
  • Solution: Turbo rebuild or replacement ($1,500-$3,000)

5.9L vs 6.7L: Which is Better?

5.9L Cummins Advantages:

  • ✅ Simpler design (fewer emissions systems)
  • ✅ Easier to work on
  • ✅ Lower maintenance costs
  • ✅ Legendary reliability reputation
  • ✅ Highly sought after (holds value)
  • ✅ Better fuel economy (no DPF regen)

5.9L Disadvantages:

  • ❌ Less power (305-325 hp vs 350-420 hp)
  • ❌ Less torque (555-610 lb-ft vs 650-1,075 lb-ft)
  • ❌ Older technology
  • ❌ Harder to find low-mileage units

6.7L Cummins Advantages:

  • ✅ More power and torque
  • ✅ Better towing capability
  • ✅ More modern technology
  • ✅ Quieter, more refined
  • ✅ Better emissions compliance

6.7L Disadvantages:

  • ❌ Emissions system complexity (DPF, EGR, DEF)
  • ❌ CP4 fuel pump risk (2013-2018)
  • ❌ Higher maintenance costs
  • ❌ More expensive to repair

Our recommendation:

  • For simplicity and reliability: 5.9L (if you can find one)
  • For power and modern features: 6.7L (2019+)
  • Best value: 6.7L (2007.5-2012) - good power, simpler than later models

Cummins Engine Swaps

Can you swap a Cummins into a different truck?

Yes, but it's complex and expensive:

Common swaps:

  • Cummins into older RAM (pre-Cummins models)
  • Cummins into Ford or Chevy trucks
  • Cummins into classic trucks

Swap costs:

  • Engine: $5,000-$15,000
  • Transmission: $2,000-$5,000 (must handle torque)
  • Adapter plates and mounts: $1,000-$2,000
  • Wiring and electronics: $1,500-$3,000
  • Exhaust fabrication: $800-$1,500
  • Cooling system: $500-$1,200
  • Labor: $3,000-$8,000
  • Total: $14,000-$35,000+

Our recommendation: Only swap if you're building a custom truck or have a specific project. For daily drivers, replace with the same engine your truck came with.

What to Look for in a Used Cummins Engine

1. Mileage Recommendations

  • 5.9L Cummins: Under 200,000 miles (can go higher with good maintenance)
  • 6.7L Cummins: Under 150,000 miles

Cummins engines are so durable that 200,000-mile units are often excellent choices if well-maintained.

2. Maintenance History

Critical for Cummins:

  • Regular oil changes (every 5,000-7,500 miles)
  • Fuel filter changes (every 15,000 miles)
  • Lift pump replacement history (5.9L)
  • Injector service records
  • Emissions system maintenance (6.7L)

3. Modifications

Ask about:

  • Has engine been tuned or modified?
  • Emissions delete? (affects legality and warranty)
  • Upgraded turbo or injectors?
  • Lift pump upgrade? (good for 5.9L)

Avoid heavily modified engines unless you know the history.

4. Compression Testing

Demand results:

  • All cylinders within 10% of each other
  • Readings within Cummins specifications (typically 350-450 psi)

5. Leak-Down Test (If Possible)

  • More accurate than compression test
  • Shows cylinder seal quality
  • Should be under 10% leakage per cylinder

6. Warranty Coverage

  • Minimum 1-year warranty
  • Preferably 2-3 years
  • Understand what's covered (internal components vs accessories)

Cost Comparison: Cummins Engine Replacement

Example: 2015 RAM 2500 with 6.7L Cummins failure

New Engine from RAM Dealer:

  • Engine: $12,000-$16,000
  • Installation: $2,500-$3,500
  • Total: $14,500-$19,500
  • Warranty: 3 years/36,000 miles

Remanufactured Engine:

  • Engine: $8,000-$11,000
  • Core charge: $1,500-$2,000
  • Installation: $2,500-$3,500
  • Total: $12,000-$16,500 ($10,500-$14,500 after core return)
  • Warranty: 2-3 years

Quality Used Engine (Used Engines Store):

  • Engine (120,000 miles): $6,000-$9,000
  • Installation: $2,500-$3,500
  • Total: $8,500-$12,500
  • Warranty: Up to 3 years
  • Savings: $6,000-$7,000 vs new

For a RAM 2500 worth $35,000-$50,000, the used Cummins offers excellent value while maintaining legendary diesel capability.

Installation Considerations

What to replace during Cummins installation:

All Cummins Engines:

  • Oil and filter (15W-40 diesel oil, 12 quarts)
  • Fuel filter
  • Coolant
  • Thermostat
  • All gaskets and seals

5.9L Specific:

  • Lift pump (upgrade to aftermarket)
  • Injection pump seals
  • Grid heater inspection

6.7L Specific:

  • Turbo oil feed and return lines
  • EGR cooler inspection
  • DPF/DEF system check

Total parts investment: $600-$1,500

How Long Does Cummins Replacement Take?

Typical labor time:

  • RAM 2500/3500: 16-24 hours (3-5 days)
  • Nissan Titan XD: 18-26 hours (4-5 days)

Why it takes longer:

  • Heavy engine (1,100+ lbs)
  • Complex emissions systems (6.7L)
  • Transmission removal often required
  • Diesel-specific procedures

Pro tip: Use a shop experienced with Cummins diesels. Diesel work requires specialized knowledge and tools.

Cummins Maintenance for Longevity

How to get 500,000+ miles:

1. Oil Changes

  • Every 5,000-7,500 miles (not 10,000+)
  • Use quality 15W-40 diesel oil
  • Change filter every time

2. Fuel System Maintenance

  • Change fuel filter every 15,000 miles
  • Use quality diesel fuel (avoid cheap stations)
  • Add fuel treatment in winter
  • Upgrade lift pump (5.9L)

3. Cooling System

  • Flush coolant every 60,000 miles
  • Inspect hoses and clamps
  • Replace thermostat preventively

4. Let It Warm Up

  • Idle 3-5 minutes before driving in cold weather
  • Don't lug engine when cold

5. Let It Cool Down

  • Idle 2-3 minutes after towing or hard driving
  • Allows turbo to cool properly

6. Address Problems Early

  • Don't ignore warning lights
  • Fix leaks immediately
  • Replace worn components before failure

Why Choose Used Engines Store for Your Cummins?

We specialize in Cummins diesel engines:

  • 5.9L and 6.7L Cummins available
  • VIN matching - Perfect compatibility for your RAM or Nissan
  • Low-mileage inventory - Most engines under 150,000 miles
  • Compression tested - Every engine verified before shipping
  • Maintenance history when available
  • Up to 3-year warranties - Real protection for your investment
  • Nationwide shipping - Fast delivery anywhere in the USA
  • Expert Cummins knowledge - We understand what makes these engines legendary

Get Your Cummins Engine Quote Today

Ready to restore your truck's legendary Cummins power?

What we need from you:

  • Your truck's VIN (17 characters)
  • Year, make, and model
  • Current engine (5.9L or 6.7L)
  • Current mileage
  • Brief description of the problem

What you'll receive:

  • VIN-matched Cummins engine quote within 24 hours
  • Engine specifications and mileage
  • Warranty details (up to 3 years)
  • Shipping cost and timeline
  • Installation recommendations

Contact us today:
Email: support@usedenginesstore.com
Address: 30 N Gould St Ste R, Sheridan, WY 82801 USA

Get your truck running strong again with a legendary Cummins diesel engine backed by real warranty protection. Whether you need a 5.9L or 6.7L, we'll help you find the perfect replacement engine.

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