Mercedes-Benz SLC 250 d
Widely used Mercedes diesel with aluminium block and steel liner. High mileages possible but known for injector seal issues, timing chain stretch and EGR problems.
Diesel Roadster: Convincing
150 kW CDI in the SLC — more fun than expected. The diesel torque pushes hard, the roadster character survives. A smart choice for high-mileage drivers.
Engine Weaknesses 6
Over 100,000 vehicles recalled: the chain tensioner seal leaks, allowing engine oil to drip onto the exhaust system and potentially ignite.
Symptoms: Dropping oil level, oil smell from engine bay, oily deposits under the vehicle, possible oil fire
The OM651 uses a simplex timing chain. With short-trip driving and overdue oil change intervals the chain stretches.
Symptoms: Light rattling noise on cold start from the rear of the engine, no fault code stored
Same Delphi piezo injector problems as in the DE18: 220 CDI and 250 CDI variants affected. Mercedes replaced them with solenoid injectors as part of a service action.
Symptoms: Vibrations and rough running especially under acceleration, elevated fuel consumption
The EGR cooler of the OM651 develops hairline cracks at the connection stub and loses coolant. Green staining next to the fuel filter under the engine cover is typical.
Symptoms: Dropping coolant level without visible leak, intermittent coolant warning, green spots under the vehicle, heater output diminishing
The DMF on the OM651 suffers under the high torque output. Documented case: all 8mm rivets sheared at 149,000 km, with consequential damage to the clutch and crankshaft speed sensor.
Symptoms: Rattling and juddering at warm idle, vibrations when pulling away, shuddering at low RPM, noise increases with warm engine
From around 150,000–180,000 km the OM651 turbocharger leaks oil through worn bearings, which drips onto the EKAS intake port deactivation actuator and destroys it. Double damage.
Symptoms: Black smoke under acceleration, oil residue in charge air hose, power loss, fault code P0299 boost pressure underrun
Vehicle Weaknesses 6
Mercedes recalled SLK/SLC R172 between January and March 2016 due to incorrectly tightened inner track rod ends. Incorrectly torqued bolts could lead to loss of steering. Dealers inspected and replaced affected parts free of charge.
As with the predecessor SLK R171, the SLC R172 (facelift from 2016) also develops leaks at the vario roof when seals age or become brittle through UV exposure. The sealing of the metal folding roof in the area of the roof rails requires regular maintenance.
On the SLC R172, shock absorbers and suspension components are the primary weak point at higher mileages from around 80,000-100,000 km. The sportily tuned AMG Sport suspension wears faster than the standard setup.
The SLC R172 has increased quiescent current draw from numerous comfort and assistance systems. With frequent short trips or prolonged standing, the starter battery discharges, especially when used seasonally as a summer car.
On the SLC 220d, the 7G-Tronic automatic jerks uncomfortably during diesel particulate filter regeneration. The vehicle pulls briefly and abruptly -- particularly unpleasant in urban traffic. A software update can reduce this behaviour.
Like the predecessor SLK, SLC R172 owners also report noises from door cards and the rear bulkhead, which worsen at higher mileages. Temperature changes encourage plastic and rubber parts to expand.