Mercedes-Benz GL 320 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

At higher mileages from around 150,000 km, air struts and the compressor fail. The vehicle drops on one or both axles. Rear axle is most frequently affected.

Rear brake lines and rear subframe are prone to heavy corrosion on older examples. Particularly on vehicles from high-salt regions.

The 7G-Tronic transmission is prone to jerky gear changes at high mileage, particularly in gears 2–4 on kickdown.

Air bags become porous through rubber hardening and lose air. Compressor runs continuously. Aftermarket replacement air bags 95–130 EUR, original Mercedes approx. 700 EUR.

Thin underbody protection. Subframe and rear axle rust from the inside. Assessed as safety-critical at inspection.

If leaks are not promptly repaired the compressor overheats from continuous operation. Compressor replacement 500–1,000 EUR, original up to 1,300 EUR.