The 2015 S600 with the M279 6.0L twin-turbo V12 is a flagship luxury sedan plagued by catastrophic engine failures stemming from poorly-designed hot-V turbos that cook the cylinder heads and valve stems. When these engines let go, they let go hard—expect five-figure repair bills that often exceed the car's used value.
Catastrophic Engine Failure - Valve Stem Seal / Piston Ring Failure
Common · high severityTypical onset: 40,000-80,000 mi
Symptoms: Excessive blue smoke on startup that persists, Oil consumption 1+ quart per 500-1000 miles, Check engine light with misfire codes (P0300 range), Loss of power and rough idle, Catastrophic bearing failure if run low on oil
Fix: The hot-V turbo design cooks valve stem seals prematurely, leading to oil burning. Once seals fail, oil consumption accelerates and contaminates cylinders, scoring bores and failing rings. Proper fix requires full engine rebuild or short block replacement: 60-80 hours labor including removal, machining, new pistons, rings, bearings, head work, turbo reseal, and reinstall. Many shops won't touch these—expect specialized Mercedes independent or dealer-only work.
Estimated cost: $35,000-55,000
Connecting Rod and Main Bearing Failure
Occasional · high severityTypical onset: 50,000-90,000 mi
Symptoms: Knocking or ticking noise from lower engine that worsens with RPM, Metallic debris in oil during changes, Sudden catastrophic engine seizure, Oil pressure warning light, Check engine light with low oil pressure codes
Fix: When owners ignore early oil consumption issues or extend service intervals, bearing surfaces get starved and fail. Rod knock means the crank needs measuring, bearings replaced, and often crank grinding or replacement. If a rod lets go, you're looking at complete short block replacement—same 60-80 hour ordeal as above. This is a total-loss scenario for most owners.
Estimated cost: $38,000-60,000
Transmission Oil Cooler Failure
Common · high severityTypical onset: 60,000-100,000 mi
Symptoms: Transmission fluid in coolant (milky/pink coolant reservoir), Coolant in transmission (burnt smell, slipping, harsh shifts), Transmission overheating warnings, Engine overheating in severe cases, Erratic shifting or limp mode
Fix: The 7-speed MCT transmission cooler is integrated into the radiator assembly and fails internally, cross-contaminating fluids. Requires new radiator, complete transmission fluid flush (often multiple cycles), filter, and pan. If contamination is severe, transmission internals get damaged requiring rebuild or replacement. Caught early: 8-12 hours. With transmission damage: add 25-35 hours. DO NOT drive once fluids mix.
Estimated cost: $2,500-4,500 early / $15,000-25,000 with trans damage
Transmission Mount Failure
Common · medium severityTypical onset: 50,000-80,000 mi
Symptoms: Clunking when shifting from Park to Drive or Reverse, Vibration through chassis at idle in gear, Harsh engagement into gear, Driveline shudder during acceleration
Fix: The MCT transmission is heavy and the mounts fatigue from the V12's mass and torque. Rubber deteriorates and hydraulic mounts leak. Requires lifting the transmission slightly to access—2.5-4 hours for both motor and transmission mounts together. Use OEM or Corteco—aftermarket junk fails in 10k miles.
Estimated cost: $800-1,500
Fuel System Contamination / Filter Clogging
Occasional · medium severitySymptoms: Rough idle and stumbling acceleration, Long crank time before starting, Limp mode or reduced power warnings, Fuel pressure fault codes (P0087, P0088), Stalling when hot
Fix: The V12 uses high-pressure direct injection with tight tolerances. Contaminated fuel or degraded in-tank pump screens starve the system. Fuel filter is integrated into the pump module requiring tank drop—5-7 hours. If injectors are clogged, add removal, cleaning or replacement of all 12, plus calibration: additional 8-12 hours. Premium fuel and annual fuel system cleaner treatments help prevent this.
Estimated cost: $1,200-2,000 filter / $4,500-7,500 with injectors
Turbocharger Oil Feed Line and Seal Leaks
Occasional · medium severityTypical onset: 70,000-110,000 mi
Symptoms: Oil smell in cabin or visible smoke from engine bay, Oil pooling on top of engine or dripping underneath, Blue smoke under boost, Reduced boost pressure or limp mode, Oil consumption without external leaks visible from below
Fix: Hot-V configuration roasts the turbo oil feed and return lines, causing hardening and leaks. Lines run between cylinder banks and are a nightmare to access. Requires partial engine disassembly, intake removal—12-18 hours. If turbo seals have failed from oil starvation, add turbo replacement: 20-28 hours total. This job sucks and most shops will sublet to a specialist.
Estimated cost: $3,500-6,000 lines only / $8,000-14,000 with turbos
Absolutely not—unless you're paying cash, have a $20k emergency fund earmarked for engine replacement, and accept it's a financial black hole. Buy the V8 S550 instead.
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.