Mercedes-Benz E 350 CDI

The best-known problem of the OM642: the oil cooler gaskets in the V-section of the engine fail. Oil leaks into the coolant or externally. Particularly prone on vehicles built up to 2009.

Symptoms: Oil loss warning, oil spots under the left side of the vehicle, oil streaks visible on the belt tensioner

The plastic linkages of the swirl flaps in the OM642 intake manifold break. Aluminium repair kits are available and more durable. In the event of complete failure there is a risk of debris entering the engine.

Symptoms: Engine warning light, fault codes for intake flap/swirl flap, power loss particularly at low rpm

Piezo injectors seal poorly from heat, diesel enters the engine oil. Oil loses lubrication properties, tar-like residue around injectors is the typical telltale sign.

Symptoms: Rough idle, increased fuel consumption, knocking noises, oil level rising due to diesel contamination, engine oil smells of diesel

Variable turbine geometry actuator linkage seizes due to soot deposits. Engine enters limp mode. Fault codes P0404, P2598, P2385. If runner damage occurs, turbo costs from €1,300.

Symptoms: Sudden power loss on kickdown, limp mode, black smoke, engine oil in intercooler area

The standard oil pump delivers insufficient pressure at high revs and temperatures. No warning in the cockpit. Connecting rod bearings wear unnoticed between 150,000–200,000 km, total engine failure looms.

Symptoms: Cold knocking at idle, metallic rattling during load changes, fine metal particles in oil filter, oil pressure drop only measurable late

With frequent short-trip driving the EGR system on the OM642 becomes heavily coked. Soot deposits in the intake manifold significantly reduce airflow.

Symptoms: Power loss particularly under load, poor throttle response, soot clouds, elevated fuel consumption

Thin-walled glow plugs corrode in the cylinder head and break during removal. Broken heating element requires time-consuming drilling out. Replace all 6 plugs preventively.

Symptoms: Difficult cold starting, extended pre-glow time required, glow indicator flashes, white smoke at cold start in winter

Rear subframe rusts from the inside out. Faulty factory sealant allows water ingress. Flagged as safety-critical at MOT.

W212 steel rear subframe with powder coating cracks over time and allows moisture in. Rusts from the inside. Mercedes replaces as a goodwill gesture. Safety-critical.

Brake lines above the rear axle corrode through after 8–10 years. Brake fluid loss leads to brake failure. MOT refusal.

Airmatic system fails through compressor defects and air bag leaks. Vehicle drops. Rear axle often has to be removed.

Rear axle corrodes through with age; suspension mounting points are flagged at MOT. Goodwill repairs possible but time-limited.

Brake lines corrode at two to twelve times the rate of comparable vehicles according to MOT data.

The rear axle is prone to severe rust-through from the inside at the weld seams of the subframe. The problem goes unnoticed for a long time. Mercedes granted goodwill replacements in some cases.

Worn joints and strut rod ends on the front axle are a recurring problem. Classic wear pattern at higher mileages.

Drain holes in the sills clog up; water collects and promotes rust from the inside.

Worn ball joints and strut top mounts on the front axle are a recurring problem. Individual owners reported multiple repairs.

The soft top tends to develop cracks in the fabric after about 10 years. Ignored cracks lead to water ingress, mould growth and control unit damage.

The drain channels in the sills clog regularly, causing water accumulation and corrosion in the sill area. Control units in the floor area can become damp.