Mercedes-Benz S 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.
World's First V8 Diesel — Redefined the Diesel Saloon
World premiere 2000: the S 400 CDI debuted the first V8 diesel in automotive history. 570 Nm at near idle, yet quieter than any six-cylinder diesel of its era. Historically significant, effortlessly brilliant to drive.
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 6
The Airmatic compressor runs continuously when there are leaks in the system and burns out. Without swift intervention, total suspension failure and blocked ride-height control follow.
Air spring bag seals age and become leaky. The vehicle drops on one side or completely. All four struts typically need replacement by around 250,000 km.
Three SAM modules in the engine bay and interior are vulnerable to water ingress through blocked drain channels. Secondary damage can exceed the vehicle's residual value.
The hollow-section sills of the W220 rust from the inside out. Nothing is visible externally for a long time until the rust is already well advanced. Pre-facelift models (1998–2002) are particularly affected.
The W220 rusts at the underbody, wheel arches and weld seams, particularly where underbody protection has not been renewed regularly.
Electric window regulators are not rated for the weight of the W220 double-glazed windows and wear out prematurely. Driver's side particularly affected.
Reports & Tests
289 owner complaints filed with NHTSA (1998–2005). Most reported: Electrical (108), Suspension (68), Lighting (24).