Mercedes ML350 CDI OM642

The Mercedes ML350 CDI OM642 has a reliability score of 48/100, rated "RISKY". Capable diesel, expensive gremlins lurk within

The most frequently reported issues are Timing Chain & Tensioner Wear, Oil Cooler Seal Failure, EGR Valve & Swirl Flap Issues, Turbocharger & Actuator Fragility, among others. See the Known Issues section above for symptoms, affected mileage, and repair costs.

Yes, this is a documented issue on the OM642, typically appearing around 120,000-250,000 km. The OM642 timing chain and tensioner are a well-documented failure point. Chain stretch is common, particularly on older dual-row chain variants. A worn tensioner can allow chain slack, leading to rattles on cold start and, if neglected, catastrophic engine damage. Reported cases of excessive chain wear correlate strongly with poor or infrequent oil changes. Typical repair cost: €1,500-4,000. DIY difficulty: Hard.

Yes, this is a documented issue on the OM642, typically appearing around 100,000-200,000 km. The oil cooler seals are widely regarded as the OM642's most notorious recurring weakness. Failure causes oil and coolant cross-contamination or external leaks. Replacement is labour-intensive due to the engine's V6 layout and the cooler's buried position, making labour cost the dominant factor. Typical repair cost: €800-2,500. DIY difficulty: Hard.

Yes, this is a documented issue on the OM642, typically appearing around 100,000-180,000 km. EGR valve clogging and swirl flap failure are common across OM642-equipped vehicles. A stuck or seized swirl flap actuator can result in power loss, especially above 2,000 RPM. EGR issues cause carbon buildup in the intake manifold, reducing efficiency and throttle response. Typical repair cost: €400-1,200. DIY difficulty: Moderate.

Yes, this is a documented issue on the OM642, typically appearing around 150,000-250,000 km. The OM642 turbo actuator is more fragile compared to older Mercedes diesel engines. Actuator failure leads to limp mode and power loss. Full turbo failure, while less common than actuator issues, is expensive to rectify given the V6 configuration. Typical repair cost: €1,200-3,500. DIY difficulty: Hard.

Yes, this is a documented issue on the OM642, typically appearing around 100,000-180,000 km. Valve cover gasket leaks are reported on the OM642, often discovered during other maintenance. The V6 layout means both banks can develop leaks. The turbo bracket mounting area and surrounding seals are also noted leak points, sometimes discovered when investigating the oil cooler. Typical repair cost: €300-900. DIY difficulty: Moderate.

The OM642 in the W164 ML350 CDI is a genuinely capable diesel V6, but it comes with a well-documented list of expensive failure points that make service history critical, not optional. A well-maintained example with oil changes every 10,000 km or less can be a rewarding ownership experience, but a neglected one will quickly expose you to a chain replacement, oil cooler job, or turbo actuator bill that can exceed the vehicle's value. Budget €2,000-4,000 for preventive work if service history is incomplete or unknown. Only buy with a full pre-purchase inspection from an independent Mercedes specialist who knows the OM642 specifically.

The power output differences across ML280/320/350 CDI variants come from ECU tuning and turbo boost calibration, not a fundamentally different engine, so hp figure alone should not drive your buying decision. All variants share the same timing chain, oil cooler, EGR, and turbo actuator weak points. Focus on documented oil change history and cold-start chain rattle regardless of which power output you are looking at, and treat the BlueTEC facelift versions (2009 onward) as having marginally more mature emissions hardware, not a more reliable core engine.

Before buying, check: Perform a cold-start and listen for any timing chain rattle lasting more than 2 seconds before buying; Check the coolant reservoir for oily contamination and the oil filler cap for white emulsion indicating oil cooler seal failure; Request full documented service history, verify oil was changed every 10,000 km or less with correct MB 229.51/229.52 spec oil; Connect an OBD scanner and check for fault codes related to EGR, swirl flaps, turbo boost, and cam timing deviation; Inspect the engine bay for oil staining around valve covers, oil cooler area, and turbo bracket mounting points.

There's no fixed mileage limit, it depends on maintenance. The parts worth budgeting for proactively are: Timing Chain & Tensioner Kit (120,000 km), Oil Cooler Seals (100,000 km), EGR Valve (100,000 km), Turbo Actuator (150,000 km). Engines that clear these checkpoints with documented maintenance commonly continue well beyond typical ownership periods.

On certain 2007-2012 model year OM642-equipped Mercedes-Benz SUVs (ML, GL, R-Class), a fuel injector line can crack over time and leak diesel fuel in the engine compartment, creating a fire risk. Remedy: Inspection and replacement of affected fuel injector lines at an authorised Mercedes-Benz dealer.

Estimated ownership cost is €4,500-15,000 over 3 years depending on maintenance history and mileage, higher if oil cooler seals or timing chain require attention, based on known issues and typical service needs.

Owners report real-world fuel consumption of around 10.6 L/100km, compared to the official figure of 12.3 L/100km.

Community-reported real-world usage suggests changing oil every 10,000 km using MB 229.51 or 229.52 5W-30 fully synthetic diesel engine oil, often more conservative than the official service schedule.

The OM642 is also found in: Mercedes-Benz E320 CDI / E280 CDI (W211), Mercedes-Benz GL320/GL350 CDI (X164), Mercedes-Benz R320/R350 CDI (W251), Mercedes-Benz S320 CDI (W221), Mercedes-Benz Sprinter 3.0 CDI, Jeep Grand Cherokee 3.0 CRD, Chrysler 300C 3.0 CRD.

Capable diesel, expensive gremlins lurk within The biggest recurring complaint is Timing Chain & Tensioner Wear. Mixed to cautious. Community members acknowledge the engine's performance credentials but consistently flag the oil cooler seals and timing chain as the two expensive pain points. There is a strong consensus that maintenance discipline, especially oil change frequency, is the single biggest factor in whether an OM642 survives long-term. Many owners who bought without service history report regretting it.