Mercedes-Benz SL 500
4.0-litre V8 with two turbochargers in the cylinder valley — the so-called hot-inside-V arrangement keeps the exhaust paths short and virtually eliminates turbo lag. The M176 is the civilian variant of the AMG V8: same basic architecture, different mapping, not a hand-built individual unit. Water-cooled charge air coolers in the cylinder valley reduce intake charge temperature from over 140°C to near ambient. Cylinder deactivation silences four cylinders at part-load — only perceptible as minimal steering wheel vibration. Maintenance note: do not push oil change intervals, as the oil separator in the crankcase breather reacts badly to old oil and, when blocked, pushes out the valve cover gasket — extensive front-end disassembly required. Change spark plugs every 80,000 km, plan intake valve carbon cleaning after 70,000 km. When buying used, listen for wastegate rattle at part-load — addressable via Xentry. Check camshaft adjuster solenoids for oil traces at the connector.
Open V8 — classic roadster feel with BiTurbo thrust
With 455 hp and the roof open the M176 in the R231 creates a combination that is hard to top. The engine sounds more free-breathing than in the saloon, the chassis is surprisingly precise for a roadster of this class. Compared to the naturally aspirated predecessor, some linearity in the lower rev range is lost — but the low-end pull is noticeably more forceful and sustained.
Engine Weaknesses 9
The timing chains on the M176 V8 can stretch at high mileage. Due to the hot-inside-V design the repair is very complex as the turbochargers sit between the cylinder banks.
Symptoms: Chain rattling on cold start, camshaft fault codes, rough idle
The camshaft adjuster solenoid on the M176 leaks and oil migrates by capillary action through the wiring harness to the ECU. A known Mercedes V8 issue since the M278.
Symptoms: Cold-start rattle for 1–2 seconds, camshaft adjuster fault code, oil traces on connector, in extreme cases ECU failure
The coolant pump on the M176 can develop a leak at the seal. Coolant loss leads to engine overheating if not addressed.
Symptoms: Coolant level drops, coolant puddle under the vehicle, temperature gauge rises
The oil return lines of both turbochargers in the hot-V become brittle and leak from heat exposure. Oil drips onto hot engine components.
Symptoms: Oil smell from engine bay, oil spots in V-area, dropping oil level, occasional smoke
The individual ignition coils on the M176 BiTurbo V8 age faster due to the high thermal load in the turbocharged V. With 8 cylinders the costs add up quickly.
Symptoms: Rough idle, misfires on individual cylinders, check engine light, power loss especially in cold weather
The oil separator in the crankcase ventilation clogs over time and increases internal pressure, which forces the valve cover gasket to leak. Repair requires extensive disassembly of the front end.
Symptoms: Oil smell in engine bay, oil spots on valve cover and engine block, dropping oil level without visible leak in the hot-V area.
Pure direct injection without fuel rinsing of the intake valves allows oil mist from the crankcase ventilation to bake on and progressively narrow the intake ports.
Symptoms: Rough idle, noticeably reduced power at higher mileage, slightly elevated fuel consumption, occasional misfires.
The hydraulic engine mounts on the M176 are heavily stressed by the high torque (700 Nm). Hydraulic fluid leakage accelerates wear.
Symptoms: Vibrations at idle felt in the interior, clunking on throttle changes, increased noise at low rpm
The wastegate flaps on both turbochargers rattle at part throttle as the guide bush has play when cold. No mechanical consequential damage — Xentry coding provides a remedy.
Symptoms: Metallic rattling at constant part-throttle, especially pronounced when cold, disappears at full load and at idle.
Vehicle Weaknesses 8
Leaking front ABC dampers were documented on early R231 examples. A new damper from Mercedes costs 1,900 EUR; reconditioned units are available for half the price.
The ABC hydraulic oil absorbs moisture. The pH drops, rubber components dissolve and contaminate valves and lines. Annual change is mandatory.
Active Body Control loses hydraulic pressure through non-use or ageing. Valves become coated with deposits, pressure accumulators lose membrane tension. Regular Pentosin change every 50,000 km is essential.
The folding roof can develop leaks through aged seals, particularly at the side guides and in the A-pillar area.
High quiescent current draw. Battery discharges quickly with prolonged standstill. AGM battery must be maintained regularly.
Pressure lines are partly routed incorrectly from the factory and become porous through pinching. Hydraulic oil escapes and the roof stops in any position.
The vario roof develops creaking, rattling or clicking noises. Recalibration by the dealer eliminates the noises. Cost approximately 540 EUR.
The bonding of the roof seal at the transition to the windscreen detaches with age. Water runs along the A-pillar into the interior.
Reports & Tests
35 owner complaints filed with NHTSA (2012–2020). Most reported: Engine (7), Powertrain (7), Wheels (7).