The 2009 SLK55 AMG packs the M113K 5.4L supercharged V8—a hand-built powerhouse that's mechanically stout when maintained but shows an Achilles' heel around 80,000-120,000 miles: the infamous supercharger snout bearing failure that can cascade into catastrophic engine damage if ignored. Transmission cooling and mount issues are chronic annoyances.
Supercharger Snout Bearing Failure Leading to Engine Carnage
Common · high severityTypical onset: 80,000-120,000 mi
Symptoms: Whining or grinding noise from front of engine, especially on cold start or during acceleration, Sudden metallic rattling followed by loss of power, Metal shavings in oil, check engine light, limp mode, Catastrophic: snout shaft breaks, supercharger disintegrates, debris enters engine destroying pistons, rods, crank
Fix: Preventive: Replace supercharger snout bearing and coupler (~8-10 hours). If it grenades the engine, you're into full short-block or long-block replacement (40-60 hours) with machine work, gaskets, timing components, fluids. Many owners proactively rebuild the snout around 70k-80k to avoid the gamble.
Estimated cost: $2,000-3,500 preventive snout service; $15,000-25,000+ full engine rebuild/replacement if catastrophic failure occurs
Transmission Oil Cooler Line Leaks and Cooler Failure
Common · medium severityTypical onset: 60,000-100,000 mi
Symptoms: Transmission fluid pooling under front of car, Burnt transmission fluid smell, Harsh or delayed shifts when trans runs hot, Low fluid warnings if equipped with level sensor
Fix: The plastic quick-connect fittings on the cooler lines crack and the cooler itself can leak at seams. Replacement involves removing front bumper cover and sometimes radiator support. 4-6 hours labor plus flush and refill with MB-spec ATF.
Estimated cost: $800-1,500
Transmission Mount Collapse
Common · low severityTypical onset: 70,000-110,000 mi
Symptoms: Clunk or thud on hard acceleration or deceleration, Vibration at idle in Drive, Visible sag or torn rubber when inspected from below
Fix: The rear transmission mount's rubber deteriorates from heat and stress. Requires lifting trans slightly with jack, removing bolts, swapping mount. 1.5-2 hours labor, straightforward job.
Estimated cost: $300-500
Fuel Filter Clogging and Fuel Delivery Issues
Occasional · medium severityTypical onset: 90,000-130,000 mi
Symptoms: Hesitation or stumble during hard acceleration, Rough idle or misfires under load, Check engine light with lean codes or fuel trim faults, Extended crank time on startup
Fix: The in-tank fuel filter/pump assembly can clog, especially if the car sat or saw poor fuel. Requires dropping the fuel tank, replacing the pump module. 3-4 hours labor. Often combined with fresh fuel pressure regulator if the system's been marginal.
Estimated cost: $600-1,200
Head Gasket and Cylinder Head Bolt Failures
Occasional · high severityTypical onset: 100,000-150,000 mi
Symptoms: Coolant loss with no visible external leaks, White smoke from exhaust or steam at startup, Rough idle, misfires on specific cylinders, Oil-coolant mixing (milky dipstick or coolant in oil)
Fix: M113K head bolts can stretch and gaskets can fail, especially if the engine has seen overheating or detonation. Requires heads-off, machine shop resurface, ARP studs recommended, new gaskets, timing chain service while open. 20-30 hours labor depending on how far you go.
Estimated cost: $4,500-8,000
Balancer Shaft and Main/Rod Bearing Wear (High-Mileage)
Rare · high severityTypical onset: 120,000+ mi
Symptoms: Deep knock or rumble from bottom end, worse when cold, Low oil pressure at idle, Metal flakes or glitter in oil filter or drain plug, Sudden seizure or locked engine
Fix: Hard-driven or neglected M113K engines can develop bearing wear. Diagnosis via oil analysis and borescope. Requires full teardown, crank polishing or replacement, new bearings, possibly pistons/rings if cylinder wear is present. 40-50+ hours labor.
Estimated cost: $10,000-18,000
Buy one only if you're prepared for the supercharger snout service and understand the catastrophic risk of skipping it—well-maintained examples are glorious drivers, but neglected ones are financial sinkholes.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.