2006 — 2012
3.0L (OM642) V6 Turbo Diesel - R350 CDI 4MATIC
Diesel
When cold starting the engine, listen carefully for any 'rattle' from the engine bay, which could indicate potential timing chain wear common in high-mileage OM642 units.
Engage the air suspension by cycling through the vehicle's height settings; ensure the car levels out promptly and doesn't remain 'sunk' on one side after sitting overnight.
While driving at low speeds, gently apply the brakes and observe for any vibration in the pedal or steering wheel, as the W251 is known to be sensitive to worn suspension bushings and ball joints.
Inspect the underside of the engine bay for signs of oil leaking from the turbo intake seal, which can drip onto the swirl motor linkage and cause electronic faults.
Usually the time to evaluate the state of the air struts and compressor.
Often the point where the transmission fluid and filter service is critical to ensure longevity.
Typically when the DPF (Diesel Particulate Filter) may require professional cleaning or assessment of its remaining efficiency.
Prioritise a comprehensive pre-purchase inspection from an independent Mercedes specialist who has experience with the W251 platform.
Check that the transmission shifts smoothly without 'hunting' for gears or hesitating, as this suggests the need for a fluid flush.
Verify the service history specifically for oil change intervals, as the OM642 engine relies heavily on high-quality synthetic oil.
Confirm that the panoramic sunroof seals are clean and the drains are clear to prevent water ingress into the cabin electronics.
Ensure all electronic 'creature comforts' work, as the R-Class features complex wiring that can be tricky to troubleshoot if neglected.
Estimated repair costs if issues arise
In cars of this age, the rubber components of the air springs can perish. If this component needs attention in the future, the estimated cost in NZ is usually for the struts and a potential compressor refresh.
A known quirk of the OM642 engine is that the internal oil cooler seals can eventually harden and leak. Depending on the car's history, you might eventually need to budget for this, as it is a labour-intensive job located in the 'V' of the engine.
To keep the 7G-Tronic shifting as it should, a full fluid and filter service is a wise investment. If this hasn't been done recently, it's a good idea to budget for this as a preventative measure.
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Disclaimer: This report is generated with the assistance of AI analysis based on verified automotive data. While we strive for 100% accuracy, enthusiasts should always conduct physical inspections and consult service records. View Full Disclaimer