1990-1999 Mitsubishi Montero Problems & Issues

Both the 3.0L 6G72 and the 3.5L 6G74 V6s used in the 1990s Montero are interference-design engines driven by a rubber timing belt. If the belt snaps, or if it is contaminated by oil leaking from the front cover/cam seals, the pistons strike the open valves and bend them. Note that while the generic 12-valve SOHC 3.0L in some Chrysler/Dodge applications is often called non-interference, the 6G72 as installed in the Mitsubishi Montero/Diamante is confirmed by engine references and owners to be an interference motor, and the 6G74 is interference as well. Many 90s Monteros are now well past any documented belt service, making this the single most consequential neglected item on the platform.

The 6G72's crank/cam timing signal on early 1990s trucks is generated inside the distributor, and later trucks use a discrete crankshaft position sensor at the front of the engine behind the crank pulley/timing covers. As these sensors and their pickups age they fail intermittently, producing a classic 'cranks but won't start' condition or sudden stalling while driving that often clears after the engine cools. Owners repeatedly report that aftermarket sensors do not resolve the problem and that only a genuine Mitsubishi (OEM) sensor restores reliable operation; the crank sprocket tone/reluctor ring can also strip or be damaged.

As the 6G72 and 6G74 V6s age, the valve stem seals harden and crack and the piston rings/valve guides wear, allowing oil into the combustion chamber. This is one of the most widely reported 90s Montero engine complaints. Owners report consumption on the order of a quart every 1,000-1,500 miles with bluish smoke that is worst on cold startup (after the engine sits, oil seeps past the seals and burns off in a plume) and on deceleration. Note that the underlying cause is often worn valve guides, so seal replacement can be a band-aid; Mitsubishi's own spec treats ~1 quart/1,000 miles as within range for this engine family.

Mitsubishi recalled 1992-1994 Montero SUVs because a front wheel-side brake hose can crack. NHTSA's record describes the failure as occurring under conditions of full lock steering combined with full suspension travel — the kind of articulation a Montero sees when the wheels are turned to the stop or the suspension is fully extended or compressed. Either the left or right front hose can be affected. Once the hose cracks, brake fluid leaks out of the hydraulic circuit, the brake warning lamp illuminates, and braking efficiency is reduced, which NHTSA states increases the risk of a crash. The campaign covers 93,000 vehicles in total across every model included in it; that figure is campaign-wide and is not a count of Monteros.

The Montero's Super Select 4WD (second-generation, 1992+) engages the front axle through a vacuum-operated free-wheel actuator and electric solenoids rather than a mechanical linkage from the shifter. Over decades the dual-solenoid pack fails, the rubber hoses deteriorate, and the front differential actuator (a small shaft under a rubber boot on the passenger side of the front diff) can rust or seize, especially after long storage. The result is a truck that will not engage or disengage 4WD properly, gets stuck in 2WD or 4WD, grinds from the front axle, or flashes the 4WD indicator lights. This is a signature, well-documented failure mode discussed extensively in the overland/Expedition Portal community.

The Aisin-based 4-speed automatic (V4AW2/V4AW3) behind the Montero V6 develops a torque-converter lockup (damper-clutch) shudder as it ages, felt as a vibration or 'buzz' typically in the 35-50 mph range at steady throttle that owners often mistake for an engine misfire. A Mitsubishi TSB attributes this to breakdown of the ATF causing damper-clutch shudder (documented for 1999-2003 Montero/Montero Sport; on RWD trucks it can also cause rear leaf-spring chatter). Neglected or overheated fluid, common on trucks that tow or wheel, also leads to worn clutch packs, slipping, delayed engagement, and harsh or missed shifts.