Mercedes-Benz SLK 55 AMG
Naturally aspirated V8 in three displacements from 4.3 to 5.5 litres — old-school character with no turbo lag. Linear power delivery, deep rumble from 2,000 rpm building to a hoarse roar above 5,000. Peak torque at 3,000; beyond that it thins out — yet it's silky in part-throttle and surprisingly economical. Achilles heel is the seals: rear crankshaft oil seal practically universal above 150,000 km (gearbox removal required, 600–900 EUR), valve covers and oil filter housing seep with age. All cheap parts. The one critical point: the rubber damper on the crankshaft pulley hardens with age — when it fails the pulley machines into the sump. Replace preventively every 150,000 km. Oil changes every 10,000 km with 5W-40, 16 spark plugs every 60,000–80,000 km — then 400,000 km is realistic.
387 hp Facelift — Revised Camshafts, More Rev Enthusiasm
27 hp more than the predecessor, revised camshafts for a more willing rev-out to 7,000 rpm — the sound gets sharper at the top. Still under 1,500 kg, still four tailpipes right behind the seats. Best value of all R171 variants — the pre-facelift is cheaper, the 400 hp version barely faster. Power steering pump as a known weak point.
Engine Weaknesses 10
The rubber damper in the crankshaft pulley hardens with age and can eat into the sump — catastrophic consequential damage. Preventive replacement every 150,000 km strongly recommended.
Symptoms: Unusual vibrations at idle, in worst case metallic scraping from below. Often no prior warning — sudden failure.
The rear crankshaft seal is leaking on virtually all M113 engines above 150,000 km. Gearbox removal required — 600–900 EUR workshop costs. If oil creeps into the torque converter it becomes expensive.
Symptoms: Oil drops or oil film visible at the engine-gearbox interface, oil loss without any other apparent leak on the engine.
Engine mounts can fail before 100,000 km. Practical test: finger between the stabiliser bar and front sump — no clearance means the mount is dead. Not visually checkable without removal.
Symptoms: Vibrations in interior especially at idle, dull rumbling on acceleration, in worst case contact between engine and bodywork.
Faulty thermostat leads to permanently low engine temperature (increased wear) or overheating in traffic jams. Part costs 24 EUR — swap it immediately on suspicion, do not wait.
Symptoms: Temperature gauge permanently below mid-point (thermostat opens too early) or engine overheats in traffic (thermostat stuck closed).
The front crankshaft seal hardens with age. More accessible than the rear seal, but the pulley bolt is a single-use part. Oil on the drive belt damages it additionally.
Symptoms: Oil film on underside of belt drive, oil visible on drive belt.
Both valve cover gaskets harden with age and allow oil through. Cheap parts (18 EUR each), but caution: aluminium bolts on the valve cover — no over-torque or the threads strip.
Symptoms: Oil smell in engine bay, visible oil film on lower valve cover edge, smoke when oil drips onto exhaust manifold.
PCV hoses become brittle and crack. Leads to pressure increase in the crankcase, elevated oil consumption and false air ingestion. All hoses together under 31 EUR — worth replacing as a set.
Symptoms: Elevated oil consumption without visible leak, white smoke from exhaust, idle fluctuations from false air.
O-ring seals on the oil filter housing and oil cooler connection harden and seep oil. Classic ageing, cheap to fix if caught early — all three seals under 30 EUR.
Symptoms: Oil film around the oil filter area, drips under the vehicle at the front of the engine.
The bolts on the intake manifold switchover loosen. They cannot fall out but cause noise and functional disturbance. Recommendation: remove intake tract, clean, secure bolts with Loctite.
Symptoms: Clattering or rattling from the intake area, irregular throttle response, slight power drop at certain rpm.
The 16 original injectors (black) wear at high mileage. Mercedes introduced revised blue injectors. O-ring seals on the injectors can leak and allow fuel into the oil.
Symptoms: Elevated fuel consumption, idle fluctuations, fuel smell on dipstick from leaking O-rings.
Vehicle Weaknesses 9
Rear axles on older R171 corrode completely through. Mercedes acknowledges this as a known problem and replaces the entire rear axle as a goodwill gesture. Immediate complaint is recommended when rust is found.
Hydraulic pump (A1718000030) loses pressure, cylinders develop leaks. Workshop estimate for new pump approximately 3,300 EUR. Used units from 230 EUR, seal kits from 39 EUR.
The rubber seal on the boot loading edge profile admits water and causes rust in the boot area. Replacing the seal prevents more serious secondary damage.
Weak or rapidly discharging battery is a common ADAC breakdown focus on the R171. Water accumulation in the blower housing due to leaf ingress can short-circuit the blower motor.
The electrohydraulic control unit (EHS) of the 7G-Tronic fails, and the gearbox sticks in one gear. A vehicle restart temporarily resolves the problem. Regular transmission oil change every 50,000-60,000 km helps prevent this.
The rubber seal at the roof above the side window bends or detaches. Water enters at the A-pillar into the interior. Seal replacement at Mercedes approximately 300 EUR.
Defective seat heating is one of the most common problems on the R171. The driver's side fails first. Specialist repair can be expensive. Drainage channels must be cleaned regularly.
Shock absorbers and suspension springs are flagged by MOT inspectors at higher mileages. The vario roof seal between the door glass and roof skin can deform and become expensive.
Limit switches in the roof mechanism stick due to oil spray residue or contamination. Faulty switches interrupt roof operation in any position.
Reports & Tests
114 owner complaints filed with NHTSA (2004–2011). Most reported: Airbags (44), Powertrain (22), Electrical (10).