Considering a used Mercedes Ml550 with over 100,000 miles on the clock? You’re likely drawn to the power and luxury this SUV offers. The ML550, especially models equipped with the M278 engine, is a sought-after vehicle. But, as with any high-performance vehicle, especially one with significant mileage, reliability and maintenance are key concerns. Let’s delve into what you need to know about owning a high-mileage Mercedes ML550 with the M278 engine.
M278 Engine: Solid Performance, Timely Service is Crucial
The M278 engine in the Mercedes ML550 is generally regarded as a robust powerplant, provided it receives diligent and timely servicing. Like any modern engine, neglecting maintenance can lead to issues down the line, especially as mileage accumulates. When considering an ML550 with over 100k miles, service history is paramount.
One area to scrutinize in the service records is the fuel injectors. Early M278 engines could experience fuel injector leaks. This isn’t just a fuel wastage problem; leaking injectors can allow fuel to seep into the wiring harness, potentially causing damage to sensitive electronic components, including the ECU (Engine Control Unit). Checking for any record of fuel injector replacement is a smart move.
Another relatively common, though minor, issue with the M278 is related to the timing chain check valve. There’s a Technical Service Bulletin (TSB) addressing this. The symptom is a noticeable ticking or slapping noise upon restarting the vehicle after it has been parked for about an hour following a drive. This noise is most audible with the windows down during a cold start. The fix, typically performed by a Mercedes-Benz dealer, involves installing a check valve to maintain oil pressure and prevent the timing chain from making noise and potentially suffering wear.
Transmission Considerations
The transmission in the Mercedes ML550 is generally durable. However, its longevity is heavily dependent on proper maintenance. A critical service item is the transmission fluid change. Mercedes-Benz recommends changing the transmission fluid at specific intervals, often around the 39,000-mile mark. Verify if this service has been performed according to schedule. If there’s no record of transmission fluid changes, it’s advisable to have it done promptly to ensure the transmission’s continued health. With regular fluid changes, the transmission should perform reliably well beyond 100,000 miles.
Blind Spot Warning System and Other Electronics
For ML550s equipped with the Driver’s Assistance Package, which includes Blind Spot Warning, there’s a potential vulnerability to be aware of, particularly in regions with harsh winter conditions and road salt. The wiring for the blind spot warning radar sensors, located in the rear bumper, can corrode over time, especially in environments where road salt or chemicals are used extensively. Failure of these sensors can trigger dashboard warning lights and, more significantly, disable Distronic features, including cruise control. Replacing the rear bumper radar sensors and associated wiring can be a significant expense, potentially reaching around $2600 if the radars themselves are damaged due to corrosion. If the vehicle history indicates it has been driven in areas with road salt, inspecting the rear bumper wiring and sensor functionality is a prudent step.
Beyond the Powertrain: Options and General Maintenance
Beyond the engine and transmission, consider the impact of optional features on maintenance. ML550s often come loaded with luxury and performance options. Features like Multi-Contour Seats, Airmatic suspension, and Active Curve Sway Bar enhance the driving experience but can also introduce additional maintenance points. For example, Airmatic struts might require replacement due to knocking noises, and the valve block for the Active Curve system could also need attention over time. These are typical maintenance items for high-end, option-rich vehicles and should be factored into the ownership costs.
Brake maintenance on the ML550 is also noteworthy. The brake rotors on the ML550 are unique in size, different from both the ML350 and the higher-performance ML63 AMG. This means replacement rotors might not be as readily available off-the-shelf and could potentially be more expensive than standard ML models.
Tire costs and wear are another consideration. The ML550 typically uses 265/45R20 tires, a size that isn’t the most common, which can sometimes lead to limited availability and potentially higher prices. Expect to order these tires in advance. Furthermore, the ML550 is a heavy vehicle, and tire wear can be accelerated, meaning tire replacement might be needed more frequently than on lighter SUVs.
Fuel economy is, as expected for a V8 SUV, not a strong point. Expect to see average fuel consumption in the range of 16-17 mpg. Windshield replacements can also be surprisingly costly, potentially ranging from $1100 to $1300, depending on vehicle options like rain sensors and heated windshields. Finally, ensure all Distronic components are functioning correctly, as repairs to these systems can be expensive.
Conclusion: Informed Ownership is Key
Owning a high-mileage Mercedes ML550 with the M278 engine can be a rewarding experience. These SUVs offer a potent blend of performance, luxury, and capability. However, like any high-performance vehicle, especially one with considerable mileage, diligent maintenance is crucial. Focus on verifying the service history, particularly regarding transmission fluid changes, fuel injectors, and timing chain check valve. Be mindful of potential issues related to options like the blind spot warning system and air suspension, and factor in the ongoing costs of tires, brakes, and potential repairs.
Before purchasing a used Mercedes ML550, a Pre-Purchase Inspection (PPI) by a qualified Mercedes-Benz mechanic is highly recommended. A thorough inspection can reveal potential issues and provide a clearer picture of the vehicle’s condition and upcoming maintenance needs, allowing you to make an informed decision and enjoy your ML550 ownership experience with greater confidence.
