Mercedes-Benz SLK 350
Four-valve V6 in two basic variants: 3.5L naturally aspirated (DES 35, 185–225 kW) with direct injection and stratified charge — refined, linear, no classic naturally aspirated feel. And the 3.0L BiTurbo family (DEH 30 LA, 245–295 kW) with Nanoslide coating, twin turbochargers and water-air charge air cooler. The BiTurbo sings sonorously from 2,500 rpm and screams at the top — exceptional for a V6. Weak points: timing chain wears early when oil change intervals are pushed. Oil cooler in the V-block doesn't seal forever. Camshaft solenoids leak. On the 3.5L stratified-charge variant add NOx sensor failures from short-trip use. Early DES 35 (2011–2013) had piston slap issues. The BiTurbo unit with Nanoslide is considered more robust. Maintained with short oil change intervals (10,000–12,000 km) the engine easily lasts beyond 200,000 km.
V6 Roadster for Cruising — Grins, Not Laptimes
306 hp naturally aspirated V6 in the compact roadster: perfect as a cruiser, too comfortable to be a true sports car. The M276 sounds noticeably more present with the roof open than in closed bodies. Linear, keen to rev, no turbo lag. For those who want relaxed open-air driving with sufficient power, this is one of the best combinations in the range. No adrenaline rush, but a broad grin.
Engine Weaknesses 10
Known weak point: the oil cooler gasket in the V-block of the M276 ages and starts leaking. Repair is extremely labour-intensive because the engine must be partially disassembled — cost €1,700–3,800.
Symptoms: Oil spots under the vehicle, rainbow sheen on wet road, dropping oil level, oil smell
Known damage pattern on all newer Mercedes engines: solenoid valves leak, oil migrates into the wiring harness. First the lambda sensors die, then the ECU. Repair documented up to €1,970.
Symptoms: Check engine light with camshaft fault code, lambda sensor failure, oil film on connectors, in extreme cases ECU failure
On early M276 DES 35 (build years 2011–2013) pistons can loosen due to cylinder bore wear. Knock noise on cold start, worst case engine damage.
Symptoms: Clacking and knocking on cold start from the engine area, getting louder over time, rough idle when cold
The two-stage chain drive system of the M276 receives insufficient oil on early engines, leading to premature chain wear.
Symptoms: Rattling on cold start, rough idle, in the worst case chain jump
The M276 has a plastic thermostat housing that cracks with age and loses coolant. The thermostat itself can also fail open.
Symptoms: Coolant loss, puddle under the vehicle, fault code P0128, engine runs too cold on motorway, temperature gauge fluctuates
The M276 PCV system with oil separator is known for failures from defective membranes or blocked valves. Increased oil consumption and power loss from false air ingestion.
Symptoms: Noticeably rising oil consumption, blue smoke from exhaust, crankcase breather fault code P052E, power loss
On the M276 DES 35 (stratified-charge variant) the NOx sensors in the exhaust stream fail. Moisture accumulates at the sensor — short-trip driving prevents it from burning off. Repair costs €900–1,200 per sensor.
Symptoms: Check engine light, NOx sensor fault code, possibly increased fuel consumption and harder starting
The exhaust manifold can crack from thermal shock — especially on sportily driven examples and early build years. Welding repair is possible but not lasting.
Symptoms: Unusually loud exhaust note, power loss, exhaust smell in the engine bay or cabin, incorrect lambda sensor readings
On M276 BiTurbo variants, the wastegate linkage on the turbochargers can develop play and rattle. A progressively louder metallic noise from the turbo area. Turbocharger replacement required.
Symptoms: Metallic clattering and rattling from the engine area, especially under load, gets worse over months, boost pressure fault code
Direct injection on the M276 V6 causes carbon deposits on the intake valves. Cleaning is necessary at higher mileages.
Symptoms: Stumble when accelerating from part throttle, rough idle, slight increase in fuel consumption
Vehicle Weaknesses 6
On the SLK R172, water penetrates through the seal of the folding metal roof in heavy rain, particularly on early production years up to approximately 2013. The seals in the area of the top left roof rail are most affected.
Early SLK R172 models up to approximately 2013 were delivered with a polycarbonate roof panel (panoramic roof) prone to cracking and leaks. The glass roof (standard from 2013) is considered significantly more robust.
Shock absorbers are the only noteworthy suspension weak point on the SLK R172. At higher mileages from approximately 100,000 km, shock absorbers and springs become more noticeable. The sportily tuned AMG Line suspension wears faster.
The COMMAND navigation system freezes or crashes; voice control becomes unresponsive. Software updates often only temporarily fix the problem. Early build years 2011-2012 are most affected.
The film of the optional Magic Sky Control panoramic roof detaches from the carrier material and is visible from outside. Mercedes classified this as a visual defect. Early polycarbonate roofs (up to mid-2012) are also prone to cracking.
Many SLK R172 owners report annoying creaking and crackling noises from door cards and the rear bulkhead, particularly during temperature changes. The open body structure makes roadsters generally more susceptible to such noises.
Reports & Tests
26 owner complaints filed with NHTSA (2011–2016). Most reported: Body Structure (7), Other (6), Fuel System (3).