Mercedes-Benz ML 500
Large-displacement naturally aspirated V8, second generation with variable valve timing on all four camshafts. Technically related to the M272 V6 — shares its known balance shaft sprocket problem on build years before 2007 (engine number below 088611). From that number the sprocket was made of hardened steel. Check early engines for fault codes P0016/P0017 and cold-start chain noise. The 5.5-litre with 285 kW is the typical variant; the 5.0-litre with 225–250 kW is somewhat more forgiving in heavier vehicles. The M278 BiTurbo successor is more efficient and more powerful, but sounds considerably less characterful — the M273 is the last true naturally aspirated V8 from Stuttgart. Pre-purchase: always check for camshaft adjuster leaks (oil in wiring harness) and thermostat fault P0128. Oil changes every 10,000 km with MB 229.5.
ML 500 W164 — V8 SUV with Touring Qualities
286 kW in the ML W164: the vehicle is heavy and tall, the engine has to work. Sovereign on the motorway, thirsty in town (13–16 litres real-world). Limited off-road capability — the engine is built for road and motorway. No driving-pleasure machine, but an impressively relaxed long-distance companion with V8 reserves.
Engine Weaknesses 9
The M273 V8 shares the balance shaft sprocket issue with the M272 V6. The soft composite material of the sprocket wears down, causing timing chain rattle.
Symptoms: Fault codes P0016/P0017, chain rattling, rough idle, power loss
As with the similarly-designed M272, the solenoid valves leak. The V8 has 4 per bank — consequential costs are particularly high due to more solenoids. Oil migrates by capillary action all the way to the ECU.
Symptoms: Check engine light with camshaft fault codes P0014/P0015/P0021/P0025, lambda sensor failures, in extreme cases ECU failure
Like the M113, the valve cover gaskets on the M273 V8 become porous over time. With a V8 having two cylinder heads, the workload doubles.
Symptoms: Oil spots under the vehicle, oil smell after hard driving, oily engine bay
Identical to the M272: plastic linkages on the variable intake flaps become brittle and break. Fault code P2006 is typical.
Symptoms: Check engine light with P2004–P2006, minimal power loss at certain rpm
The 3-disc thermostat on the M273 V8 fails prematurely in the open position. On motorway driving coolant temperature drops to 75–86°C. Difficult to access in the V8 engine bay.
Symptoms: Coolant temperature fluctuates between 75–102°C depending on load, engine does not reach operating temperature in cold conditions, fault code P0128
The M273 V8 frequently shows sporadic misfires from aged ignition coils. Water in the plug well through porous seals accelerates failure.
Symptoms: Hesitation on acceleration, rough engine running, fault codes P0301–P0308, check engine light flashes with heavy misfires
As mileage increases the M273 V8 shows noticeable oil consumption. 32 valve stem seals wear simultaneously. Above approx. 0.5 L/1,000 km intervention is needed. When doing the balance shaft repair, renew seals and rings at the same time.
Symptoms: Blue smoke on cold start or after long overrun phases, dropping oil level between service intervals, oil consumption above 0.5 L/1,000 km
The throttle body is prone to heavy carbon buildup from approx. 120,000 km. Idle hesitates and vibrates, throttle response lags on load changes. Cleaning is possible but requires a basic adaptation with a diagnostic tool.
Symptoms: Rough idle at operating temperature, slight hesitation on pull-away, engine revs unevenly after cold start, occasional stalling
Engine mounts fatigue and no longer adequately dampen V8 vibrations. Noticeable vibrations in the interior and at the steering wheel around 1,800 and 2,400 rpm. Test: blip the throttle at idle — more than 4 cm of engine movement indicates mounts are due.
Symptoms: Noticeable vibrations at 1,800 and 2,400 rpm, dull droning in the passenger compartment, visible engine rocking when blipping the throttle at idle
Vehicle Weaknesses 7
Water enters through defective tail light seals and damages the rear SAM module. Mainly pre-facelift models up to 2008 are affected.
Airmatic air struts develop leaks, particularly at certain ride height settings. The compressor pumps continuously and eventually burns out.
The 7G-Tronic transmission control unit develops faults at higher mileages. Gear engagement becomes impossible, limp mode activates.
Aluminium steering rack bolts corrode due to road salt. If all three bolts fracture, power steering fails completely. KBA recall 012425.
Pressure reservoir, compressor and air bags are highly vulnerable. Vehicle drops on one side or completely. Repair costs are very high due to expensive original parts and high labour rates.
Brake lines under the rear axle are prone to corrosion, particularly in high-salt regions. Line clips encourage moisture accumulation. Replacement requires lowering the rear axle.
The rear SAM fails when water enters through tail lights. Result: failure of lighting, wipers and displays. Mainly pre-facelift models up to 2008 affected.