Mercedes-Benz S 320 CDI
Inline-six CDI as the top diesel of its era. Powerful and torquey but complex. Check injectors and high-pressure accumulator.
Diesel Standard
145 kW diesel. Functional and economical, emotionless.
Engine Weaknesses 6
Copper sealing washers under injectors burn through from combustion heat. Soot leakage around injectors and seized nozzles are the result. Washers not changed in time require a laborious removal procedure.
Symptoms: Soot deposits visible around injector mountings, rough running, increased consumption, starting problems when engine is hot
Oil supply lines on the OM613 turbocharger coke up, oil flow decreases. The under-supplied turbo wears its bearings prematurely. When replacing, the oil feed line must always be replaced at the same time.
Symptoms: Whistling or rattling noise during acceleration, blue smoke from exhaust, power loss, oil loss at turbo housing
The piezo injectors of the OM613 wear internally at high mileage. Increased return quantities and seating face leaks are typical.
Symptoms: Poor starting, rough idle, individual cylinders fading, increased fuel consumption
Glow plugs corrode in the cylinder head with age. When removed, they frequently snap or the hex rounds off. Drilling out and helicoil insertion required.
Symptoms: Long preheat time in cold weather, starting difficulties in winter, engine warning light; risk of breakage on change
EGR oil drips onto the inlet channel shut-off actuator motor, causing a short circuit. Fuse 24 blows and disables the boost pressure controller and EGR actuator.
Symptoms: Sudden severe power loss, limp mode, engine warning light, multiple fault codes simultaneously
The oil-water heat exchanger at the oil filter housing develops leaks through ageing O-rings. Oil runs onto the A/C compressor and collects in the sump.
Symptoms: Oil patch under vehicle (centre/front), oil film on A/C compressor, dropping oil level, smoke development
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.