The 2009 E63 AMG with the M156 6.2L V8 is a high-performance sedan with one catastrophic weakness: the engine's head bolt design leads to cylinder head lifting and cracked cylinder walls, typically requiring complete engine rebuilds. When the motor stays intact, it's a solid performer, but that head bolt issue looms over every example.
M156 Head Bolt Failure and Cylinder Wall Cracking
Common · high severityTypical onset: 50,000-90,000 mi
Symptoms: Coolant consumption with no external leaks, White smoke from exhaust on cold start, Misfires on specific cylinders (often 7 or 8), Overheating under load, Milky oil or coolant in expansion tank
Fix: Factory head bolts are too short and allow head lift under high cylinder pressures. Heads warp, crack block sleeves, wash bearings. Proper fix requires engine-out complete rebuild with aftermarket studs, block sleeving or replacement, new pistons, bearings, gaskets. 40-60 hours labor.
Estimated cost: $18,000-28,000
Transmission Oil Cooler Line Leaks
Common · medium severityTypical onset: 70,000-120,000 mi
Symptoms: Transmission fluid drips under engine area, Low fluid level warnings on dash, Burnt smell after driving, Harsh or delayed shifts when fluid gets low
Fix: Metal cooler lines running along the side of the transmission develop pinhole leaks from road salt and debris. Lines should be replaced as a set, not patched. 3-4 hours labor, requires transmission pan drop and fluid service.
Estimated cost: $800-1,400
Transmission Mount Collapse
Common · medium severityTypical onset: 60,000-100,000 mi
Symptoms: Excessive clunk on 1-2 or 2-3 upshifts, Vibration at idle in Drive, Driveline shudder during acceleration, Visible drooping of transmission tailshaft
Fix: The rear transmission mount (often called the tailshaft mount) fails from the aggressive torque and frequent full-throttle runs. Rubber tears internally. Replace with OE or upgraded polyurethane unit. 1.5-2 hours on a lift.
Estimated cost: $400-700
Camshaft Adjuster Solenoid Failures
Occasional · medium severityTypical onset: 80,000-130,000 mi
Symptoms: Check engine light with cam position correlation codes (P0016, P0017, P0018, P0019), Rough idle when engine is warm, Rattle on startup for 2-3 seconds, Slight loss of power in mid-range
Fix: VVT solenoids stick or fail, throwing timing codes. Sometimes cleaning helps temporarily, but replacement is the reliable fix. Four solenoids total (intake and exhaust per bank). 2-3 hours labor, requires valve cover removal.
Estimated cost: $900-1,600
Alternator Bearing and Regulator Failure
Occasional · medium severityTypical onset: 90,000-140,000 mi
Symptoms: Squealing or grinding from front of engine, Battery warning light intermittent or steady, Voltage fluctuations (below 13V or above 15V), Multiple electrical faults stored in system
Fix: High-output alternator (200+ amps) works hard and bearings or voltage regulator fail. Replacement is typical, rebuilds are hit-or-miss. Serpentine belt off, two bolts, electrical connectors. 1.5 hours labor.
Estimated cost: $800-1,300
Balance Shaft Gear Wear (Pre-MY2008 Design Carryover Risk)
Rare · high severityTypical onset: 60,000-100,000 mi
Symptoms: Metallic rattling from deep in engine at idle, Metal shavings in oil during changes, Rough vibration that worsens over time, Catastrophic engine noise if gear teeth strip
Fix: Early M156 engines had weak balance shaft gears that could strip teeth and send metal through the engine. 2009 is borderline; some had the updated parts, some didn't. Requires engine disassembly to inspect and replace gears and chains. 25-35 hours if caught early, total loss if it grenades.
Estimated cost: $8,000-15,000
Only buy if you can afford a $20k engine rebuild or find a rare example with documented head stud upgrade—otherwise, it's a ticking time bomb wrapped in a brilliant chassis.
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.