What Are the Common 6G72 Engine Problems and How to Fix Them?

If you own a vehicle equipped with a Mitsubishi 6G72 engine—such as the Montero, Pajero, Delica, or certain Dodge and Chrysler models—you may have encountered or heard about recurring 6G72 engine problems. While this 3.0L V6 is known for its durability and smooth operation, it’s not immune to mechanical wear and design-related issues. The most common failures include timing belt breakage, oil leaks from the rear main seal, and hydraulic compensator (lifter) ticking or failure. Understanding these problems early can prevent costly repairs and extend engine life. This guide breaks down every major issue associated with the 6G72 engine, explains root causes, offers actionable fixes, and provides long-term maintenance strategies tailored to real-world ownership scenarios.

Understanding the Mitsubishi 6G72 Engine

The Mitsubishi 6G72 is a 3.0-liter SOHC or DOHC V6 gasoline engine produced from 1986 to 2018 1. It was used across various platforms including the Mitsubishi Montero (Pajero), Eclipse (early V6 models), Challenger, Diamante, as well as rebadged versions like the Dodge Raider and Chrysler Sebring coupe. With output ranging between 145–170 kW (195–230 hp) depending on configuration, the engine delivers smooth power delivery and decent fuel efficiency for its era.

Despite being naturally aspirated in most applications, the 6G72 features multi-port fuel injection, aluminum heads, and cast-iron blocks—contributing to its reputation for longevity when properly maintained. However, age and high mileage have exposed several weak points that owners must proactively manage.

Top 6G72 Engine Problems and Symptoms

Below are the most frequently reported issues based on owner forums, repair logs, and mechanic diagnostics:

🔧 1. Timing Belt Failure

One of the most critical concerns with the 6G72 is the interference design of the engine. If the timing belt snaps or jumps time, piston-to-valve contact can occur, leading to catastrophic internal damage.

• Symptoms: Engine won’t start, unusual clicking noise, misfires, or visible belt fraying
• Cause: Wear beyond recommended service interval (typically 60,000–100,000 miles)
• Solution: Replace the timing belt every 90,000 miles or 7 years, whichever comes first. Always replace tensioners, idler pulleys, water pump, and thermostat during the same job ⏱️

Many owners report that skipping the water pump replacement during a timing belt job leads to double labor costs later. Given the complexity of access, bundling components saves money long-term.

🧼 2. Oil Leaks (Valve Cover, Rear Main Seal, Front Crankshaft Seal)

Oil seepage is common on older 6G72 engines, especially after 150,000 miles.

• Common leak locations:
  • Valve cover gaskets (most frequent)
  • Rear main seal (requires transmission removal)
  • Front crankshaft seal (near harmonic balancer)
  • Oil pan gasket
• Symptoms: Oil spots under the car, burning smell, low oil level warnings
• Solution: Use OEM-spec gaskets and RTV sealant where required. For rear main seal leaks, consider using a two-piece seal upgrade kit if available for your model year.

Prevention tip: Check oil levels monthly and inspect for signs of sludge buildup, which can exacerbate sealing issues.

⚙️ 3. Hydraulic Lifter (Compensator) Ticking Noise

A persistent tapping or ticking sound at idle, especially when cold, often indicates failing hydraulic lifters.

• Cause: Debris in oil passages, worn plunger assemblies, or use of incorrect viscosity oil
• Symptoms: Audible ticking increases with RPM but doesn’t affect performance initially
• Solution: Flush oil passages, clean or replace lifters. Some mechanics recommend switching to 10W-40 oil in warmer climates to improve lifter damping ✅

Note: Persistent lifter noise without correction can lead to cam lobe wear over time.

🌡️ 4. Overheating Due to Thermostat or Radiator Issues

While not strictly an engine defect, the cooling system is closely tied to engine health.

• Causes: Stuck thermostat, clogged radiator, failed electric fans, air pockets after coolant refill
• Symptoms: Temperature gauge rising, steam from hood, loss of heat inside cabin
• Solution: Replace thermostat every 100,000 miles. Flush cooling system biennially. Bleed air from heater core by elevating front of vehicle during refill 🌐

Tip: Use OEM-style thermostats with bleed valves to prevent airlocks—a common cause of false overheating reports.

🔋 5. Misfiring and Ignition System Degradation

As the 6G72 ages, ignition components degrade, leading to misfires.

• Faulty parts: Spark plugs, plug wires, distributor cap/rotor (on older models), coil packs (on newer DOHC variants)
• Symptoms: Rough idle, CEL (Check Engine Light), poor acceleration, increased fuel consumption
• Solution: Replace spark plugs every 30,000–60,000 miles. Use NGK or Denso OEM-equivalent plugs. Inspect wires for cracks or carbon tracking 🔍

Distributor-equipped models should also check rotor button condition and cap carbon deposits regularly.

⛽ 6. Fuel Injector Clogging

Long-term use with lower-quality fuel can result in reduced injector flow.

• Symptoms: Hesitation under load, uneven idle, decreased MPG
• Solution: Perform professional fuel injection cleaning every 60,000 miles. Consider replacing with remanufactured injectors if cleaning fails to restore balance 📊

DIY option: Add a reputable fuel system cleaner (e.g., Chevron Techron) every 3rd tank to slow deposit formation.

📦 7. Intake Manifold Air Leaks

Vacuum leaks due to cracked hoses or degraded intake manifold gaskets disrupt air-fuel ratio.

• Symptoms: High idle, surging RPM, lean codes (P0171/P0174)
• Diagnosis: Use smoke test machine or propane torch method around intake runners and vacuum lines
• Fix: Replace intake manifold gasket set and inspect PCV valve/hoses simultaneously ✈️

This issue is more prevalent in hot climates where plastic components become brittle.

Engine Reliability: Is the 6G72 Long-Lasting?

Yes—the 6G72 engine is generally reliable and capable of reaching 200,000+ miles with consistent maintenance. Its simple SOHC 12-valve design (in earlier models) reduces complexity compared to DOHC versions. Owners praise its smoothness and ease of repair once familiar with layout.

However, reliability drops sharply if key services like timing belt replacement are delayed. Unlike non-interference engines, a broken belt here usually means major rebuild or replacement cost.

Component	Recommended Service Interval	Estimated Cost Range (USD)
Timing Belt + Kit	90,000 mi / 7 yrs	$600–$1,100
Spark Plugs & Wires	60,000 mi	$120–$250
Valve Cover Gasket	100,000–150,000 mi	$200–$400
Rear Main Seal	As needed (leak)	$800–$1,500
Fuel Injector Cleaning	60,000 mi	$100–$200

Costs vary significantly by region and labor rates. Independent shops typically offer better pricing than dealerships for non-warranty work.

Can You Turbocharge a 6G72 Engine?

While factory 6G72 engines were naturally aspirated, many enthusiasts have successfully added turbo systems—especially in off-road or marine applications. However, doing so requires supporting modifications:

• Lower compression pistons (to avoid detonation)
• Upgraded fuel injectors and pump
• Intercooler and reinforced cooling system
• ECU tuning or standalone engine management

Without proper tuning and component upgrades, forced induction can quickly destroy the stock bottom end. There is limited aftermarket support compared to engines like the Toyota 2JZ or Nissan RB series, making custom fabrication necessary.

How to Extend 6G72 Engine Life: Proactive Maintenance Tips

Preventing problems is always cheaper than fixing them. Follow these best practices:

1. Stick to a strict maintenance schedule—especially for timing belt, coolant, and oil changes.
2. Use quality motor oil—preferably 10W-30 or 10W-40 synthetic blend, changed every 5,000 miles.
3. Inspect belts and hoses annually for cracking, swelling, or glazing.
4. Monitor coolant condition—replace every 2 years to prevent corrosion.
5. Address small leaks immediately before they compromise other systems.
6. Keep intake and throttle body clean with periodic cleaning.
7. Warm up the engine gently before heavy loads, especially in cold weather.

Used 6G72 Engines: What to Look For Before Buying

If you're considering a replacement long block or used engine (🛒), inspect thoroughly:

• Compression test results—should be within 10% across all cylinders
• Presence of oil sludge—indicates poor maintenance history
• Timing belt condition—ask whether it was recently replaced
• Leak history—check for evidence of past rear main or head gasket leaks
• Service records—prefer engines with documented care

Rebuilt units from reputable suppliers often come with warranties and updated components, offering better peace of mind than unknown-origin cores.

Common Misconceptions About the 6G72

Several myths persist among owners and mechanics:

• Misconception: "The 6G72 is prone to head gasket failure."
  Reality: Head gaskets are durable unless the engine has suffered chronic overheating.
• Misconception: "All 6G72 engines are slow and inefficient."
  Reality: While not a performance engine, it offers adequate power for SUVs and vans; fuel economy averages 17–22 mpg depending on vehicle weight and driving style.
• Misconception: "You can skip the timing belt if the car isn’t driven much."
  Reality: Rubber degrades over time regardless of mileage—age matters as much as distance.

Regional Differences and Climate Impact

Owners in hotter regions (e.g., Middle East, Southwest U.S.) report higher rates of cooling system stress and oil breakdown. In colder areas, condensation buildup can accelerate internal corrosion if short trips dominate usage. Salt-heavy winters increase rust risk on underhood components.

In tropical countries like Thailand or Indonesia, where many Delicas and Pajeros remain in service, regular flushing of radiators is essential due to mineral-laden water use. Marine applications require additional corrosion protection.

When to Rebuild vs. Replace

Facing major internal damage? Consider these factors:

• Rebuild if: Block is intact, budget allows, and sentimental value exists
• Replace if: Extensive damage (cracked block, bent rods), time-sensitive repair needed, or sourcing parts is difficult

Remanufactured engines from companies like Powertrain Products offer factory-level specs and warranties, though prices range $2,500–$4,000 installed.

Frequently Asked Questions (FAQs)

❓ What cars did the 6G72 engine come in?

The 6G72 was used in the Mitsubishi Montero/Pajero, Challenger, Diamante, Eclipse (1st gen V6), Delica, Sigma, and also appeared in the Dodge Raider, Chrysler Sebring coupe, and some Hyundai and Mahindra models through partnerships.

❓ How much horsepower does a 6G72 engine have?

Output varies by model and year: SOHC versions produce around 145–155 kW (195–210 hp); DOHC variants reach up to 170 kW (230 hp). Torque ranges from 260–280 N·m (190–205 lb-ft).

❓ Is the 6G72 a turbo engine?

No, the factory 6G72 is naturally aspirated. However, aftermarket turbo kits exist for performance builds, requiring supporting modifications to handle boost pressure safely.

❓ Can a broken timing belt destroy my 6G72 engine?

Yes. The 6G72 is an interference engine, meaning that if the timing belt fails, the pistons can strike open valves, causing severe internal damage including bent valves and damaged pistons.

❓ How often should I change the oil in a 6G72 engine?

Every 5,000 miles or 6 months is recommended, especially for older engines or those operating in extreme conditions. Using high-quality synthetic blend oil helps protect aging seals and internals.