6B31 Engine

Mitsubishi 3.0 V6 MIVEC (6B31) – Experiences, problems, fuel consumption and used car buying guide

If you’re looking for the “last of the Mohicans” in the world of modern SUVs, the Mitsubishi 6B31 3.0 V6 is an engine that truly awakens nostalgia. This is not a small turbo engine struggling to cope; this is a thoroughbred naturally aspirated unit of the old school. Primarily installed in the Mitsubishi Outlander II (XL) and the robust Pajero Sport, this engine offers silky-smooth operation and linear power delivery that diesels simply cannot replicate.

However, owning a V6 petrol engine in Europe comes at a price – both literally and figuratively. Is the sound of a straight-six and the reliability of Japanese engineering worth the high fuel consumption? Below we dissect every bolt of this engine.

Key points in short (TL;DR)

• Reliability: Extremely high. With regular maintenance this engine easily surpasses 400,000+ km.
• Timing service: It uses a timing belt, not a chain. Timely replacement is mandatory.
• LPG: An ideal candidate for LPG conversion due to indirect fuel injection.
• Fuel consumption: High. In the city expect 13 to 16 liters, so LPG is almost a must for economical driving.
• Gearbox: Usually paired with a conventional automatic which is durable but requires regular oil changes.
• Main weakness: Catalytic converters can disintegrate and ceramic dust can damage the engine (rare, but dangerous when it happens).

Contents

• Technical specifications
• Reliability and maintenance
• Specific parts and costs
• Fuel consumption and performance
• Additional options and modifications (LPG/Chip)
• Gearbox: failures and maintenance
• Used car buying tips and conclusion

Technical specifications

The data in the table refers to the most common version of the 6B31 engine.

Reliability and maintenance

Timing belt or chain?

Although many Japanese V6 engines use a chain, the 6B31 uses a timing belt. This is critical information. If the belt snaps, the engine will suffer catastrophic damage (pistons hitting valves). The recommendation is to perform the major timing service at 90,000 km or at least every 5 to 6 years, whichever comes first. When replacing it, make sure to change the hydraulic tensioner, all idler pulleys and the water pump. Do not skimp on parts here; use quality Japanese kits (e.g. INA, SKF, or original Mitsubishi).

Most common issues

This engine is considered “bulletproof”, but it does have its Achilles’ heels:

• Catalytic converters: This is the most dangerous problem. Over the years and with poor-quality fuel, the internals of the front catalytic converters can start to crumble. Due to specific exhaust gas flow (EGR effect and valve overlap), ceramic dust can be sucked back into the cylinders, which leads to cylinder wall scoring and massive oil consumption. A typical symptom is the Check Engine light with fault codes P0420 or P0430.
• Oil leaks: The valve cover gaskets (there are two of them because it’s a V engine) tend to harden and start leaking after around 100,000 km, so oil can drip onto the exhaust manifold and cause a burning smell in the cabin.
• Crankshaft pulley: The rubber in the crankshaft pulley can crack and the outer ring can separate, which leads to loss of drive for the alternator and A/C. You’ll hear a characteristic knocking or squealing noise.

Oil and service intervals

The sump takes about 4.3 to 4.6 liters of oil (depending on whether you change the filter, which is mandatory). The recommended viscosity is 5W-30, but for higher-mileage engines in warmer climates, 5W-40 is an excellent choice for better protection.

As for oil consumption: A healthy 6B31 should not consume a noticeable amount of oil. Consumption up to 0.5 liters per 10,000 km is acceptable. If it burns a liter per 1,000 km, the piston rings are likely worn (often due to the aforementioned catalytic converter issue) or the valve stem seals are gone.

Specific parts (costs)

Fuel system, turbo and DPF

Good news for your wallet: This engine has NO turbocharger, no DPF filter, and no complicated high-pressure injectors.

It uses classic MPI (Multi-Point Injection) into the intake manifold. Injectors are cheap, robust and rarely cause trouble. If they do, they are easy to clean or replace at low cost. There is no high-pressure fuel pump that costs a fortune.

The EGR valve is present. It can get clogged with soot, which leads to rough idle, but unlike on diesels, here it is much easier and more successfully cleaned.

Dual-mass flywheel

Since this engine is paired with a automatic gearbox in 99% of cases, it DOES NOT have a dual-mass flywheel in the sense that manual diesels do. Instead, it uses a torque converter which transmits the power. That’s one big worry less, as there is no 500+ euro clutch and flywheel replacement.

Fuel consumption and performance

Real-world fuel consumption

Here you need to be prepared for reality. A 3.0 V6 naturally aspirated engine in a heavy SUV will never be frugal.

• City driving: Expect 13.5 to 16 liters of petrol per 100 km. In winter and heavy stop-and-go traffic, it can go up to 18 liters.
• Open road: On country roads at 80–90 km/h you can get it down to 8.5–9.5 liters.
• Motorway (130 km/h): Consumption is around 10.5 to 12 liters.

Is the engine “lazy”?

Absolutely not. With 220 hp and 281 Nm, this engine moves the Outlander and Pajero Sport with ease. There is no “turbo lag” – throttle response is instant. The 0–100 km/h sprint is usually under 9 seconds for the Outlander, which is an excellent result for this class and age. The power delivery is linear; the engine loves to rev and has a beautiful sound above 4,000 rpm when the MIVEC system kicks in.

On the motorway, at 130 km/h, the engine is relaxed (usually around 2,500–2,800 rpm in 6th gear with the automatic), which makes driving quiet and comfortable. Overtaking is safe and effortless – just press the throttle and the gearbox drops two gears.

Additional options and modifications

LPG conversion

YES, and it’s highly recommended. Thanks to MPI injection, LPG installation is straightforward (a “regular” sequential system) and relatively affordable (the system itself is mid-range in price, but you need 6 injectors and a stronger vaporizer). The engine handles LPG very well.

Important note: This engine (6B31) uses mechanical valve lifters (buckets), not hydraulic ones on all versions (data varies by market, but most require adjustment). It is recommended to install a valve lubrication system (“valve saver”) and to check valve clearances every 40,000–50,000 km when running on LPG, to prevent valve seat recession.

Chip tuning (Stage 1)

As a naturally aspirated engine, the 6B31 cannot be significantly boosted with software alone. A Stage 1 remap can give you around 10–15 hp and maybe 15–20 Nm, with a slightly better throttle response. Is it worth paying 200–300 euros for that? Probably not. It’s better to invest that money in quality maintenance or good tyres.

Gearbox: failures and maintenance

Which gearboxes are used?

With the 3.0 V6 engine you will most often find a conventional 6-speed automatic gearbox with a torque converter. This is usually the Jatco JF613E gearbox (known in Mitsubishi nomenclature as F6AJA/W6AJA). Manual gearboxes with this engine are extremely rare.

Automatic gearbox reliability and maintenance

The Jatco gearbox is very reliable and offers smooth gear changes. It’s not lightning-fast, but it is comfortable. The most common issues arise due to overheating (if you frequently tow heavy trailers or drive aggressively in the mountains) or due to old oil.

Oil change: Although manufacturers often claim “fill for life”, that is simply not true. Change the gearbox oil every 60,000 km. Use only oil that meets the Mitsubishi specification (J3 or equivalent). The cost of an oil change is “moderately expensive”, but crucial for long gearbox life. Symptoms of problems include jerks when shifting from P to D, or hesitation during gear changes.

Used car buying tips and conclusion

What to check before buying?

1. Engine noise when cold: Listen for valve ticking. Slight ticking that disappears is OK, but loud knocking can indicate camshaft issues or the need for valve adjustment.
2. 4x4 system: Check whether mode switching works properly (2WD, 4WD Auto, 4WD Lock).
3. Catalytic converter diagnostics: Make sure the catalytic converters are still present and check for any fault codes related to “Catalyst System Efficiency”.
4. Gearbox oil condition: Pull out the dipstick (if present) or check the oil colour. It should be reddish, not black, and must not smell burnt.
5. Timing belt service history: If there is no proof it has been replaced, immediately factor that cost in (it’s not cheap; it falls into the “expensive” category).

Conclusion

The Mitsubishi 3.0 V6 (6B31) is an engine for people who value reliability and comfort over fuel savings. It is intended for drivers who don’t cover huge mileages annually, or for those who will immediately install an LPG system. It is ideal for towing (boat, caravan) thanks to its strong torque and stable automatic gearbox.

If you can live with the fuel consumption and registration costs (due to displacement in some countries), you will get an engine that will serve you more faithfully than any modern diesel with DPF and AdBlue systems. Put simply, this is a “tank” of an engine.