Mercedes-Benz ML 400 CDI
Mercedes' first V8 diesel in automotive history — world premiere in 2000. Common rail at 1,350 bar, two turbos in tandem, 4.0 litres. Result: 570 Nm from 1,600 rpm, a character that no petrol engine of that class could match in composure at the time. Maintenance-intensive. Timing chain and tensioners are due around 150,000 km — not optional, mandatory. The right-hand turbocharger is the known weakness and will need replacing sooner or later. Injectors and high-pressure pump dislike poor-quality fuel. Oil every 10,000 km, Mercedes approval 229.51 or better — the engine does not forgive cutting corners on lubricant. With thorough maintenance 300,000 km is realistic. None of this is cheap, but anyone who buys a V8 diesel budgets for it.
V8 Diesel in Off-Road Form — Rare, Sonorous, Serious
A V8 diesel SUV was no given in 2001. The ML 400 CDI tows with disarming composure, sounds pleasantly full-bodied under acceleration, and never feels strained. For those to whom a V6 diesel is too ordinary.
Engine Weaknesses 6
Timing chain stretches from around 150,000 km; chain tensioner and guides wear. Cold-start rattling is a typical early warning. Left untreated, chain jump and total engine failure threaten.
Symptoms: Metallic rattling on cold start that subsides after 3-5 seconds. With severe stretch also audible at operating temperature.
The right turbocharger is the classic weak point of the OM628. Total failure of both turbos from around 90,000-100,000 km has been documented. Repair on the V8 diesel is correspondingly labour-intensive.
Symptoms: Significant power loss, blue or white smoke from exhaust, whistling noise under load.
Under extreme pressure loading, head gaskets fail. CO2 enters the cooling system; increased pressure pushes coolant out through the expansion tank. Engine removal required for repair.
Symptoms: Coolant warning light, coolant overflows from expansion tank, coolant level drops continuously.
Common rail injectors are prone to leaks at copper sealing rings and retaining bolts at high mileages. Injector failure can cause secondary engine damage.
Symptoms: Soot trails, rough running, power loss, fuel smell in engine bay. With advanced damage: starting difficulties.
The rear crankshaft oil seal between engine and gearbox leaks at higher mileages. The gearbox must be removed to replace the seal -- a labour-intensive job.
Symptoms: Oil puddle under vehicle centre to rear, oil film visible between engine and gearbox bell housing.
Recirculated exhaust gases coat the intake manifold, inlet ports and mixing housing with up to 2 cm of soot. Fuel consumption rises measurably; power drops gradually.
Symptoms: Gradual power loss, increased consumption, occasional lurching at part throttle.
Vehicle Weaknesses 7
The US-built W163 received insufficient corrosion protection from the factory. Boot lid, sills, wheel arches and bonnet are particularly susceptible.
The wiring harness at the ABS hydraulic block chafes against the wheel arch liner and causes ABS and ETS failures. A known design fault.
Brake lines are known to corrode through. Complete replacement requires removal of the rear axle, driveshaft and fuel tank. A safety-critical problem.
The automatic transmission suffers premature torque converter wear, particularly on the ML 400 CDI and with frequent trailer use.
The transfer case chain stretches from around 100,000 km and can jump. Noises on pull-away are an early warning. In the worst case, total drivetrain failure.
Ladder frame rusts heavily, particularly at the rear and at longitudinal member sections. Suspension mounting points can be so weakened by corrosion that the vehicle's roadworthiness is at risk.
Cables in the tailgate transition break through constant opening and closing. Rear screen wiper, third brake light and number plate lighting are affected.