The 2018 CLS63 AMG with the M157 5.5L BiTurbo V8 is a high-performance machine plagued by catastrophic engine bearing failures and transmission cooling issues. These are not 'if' problems—they're 'when' problems that can total the powertrain if ignored.
M157 Connecting Rod Bearing Failure
Common · high severity
Typical onset: 50,000-90,000 mi
Symptoms: Cold-start knock or rattle for 2-3 seconds that disappears when warm, Metallic ticking from lower engine block under load, Metal shavings in oil during changes, Eventually progresses to catastrophic rod knock and engine seizure
Fix: Engine-out service to replace all connecting rod bearings with updated parts. Some owners opt for full short block replacement if damage has started. Expect 25-35 labor hours for bearing replacement alone, 40+ hours for short block swap. This is THE Achilles heel of the M157—many techs recommend proactive bearing replacement at 60k miles.
Estimated cost: $8,000-15,000 for bearing job, $20,000-35,000 for short block
Transmission Oil Cooler Line Failure
Common · high severity
Typical onset: 40,000-80,000 mi
Symptoms: Red transmission fluid pooling under vehicle near firewall, Transmission temperature warning on dash, Harsh shifting or limp mode when fluid level drops, Steam from engine bay in severe cases
Fix: Replace cooler lines and often the entire oil cooler assembly mounted to the transmission bell housing. The lines corrode where they connect, and leaks happen fast. Requires transmission drop or significant access work—8-12 hours labor. Ignoring this grenades the transmission within days.
Estimated cost: $2,500-4,500
Engine Mount Collapse (Especially Right-Side)
Common · medium severity
Typical onset: 50,000-90,000 mi
Symptoms: Heavy clunk when shifting from Park to Drive or Reverse, Excessive vibration at idle that worsens with A/C on, Visible engine movement in bay during hard acceleration, Rubbing or contact sounds from engine bay over bumps
Fix: Replace both engine mounts and the transmission mount as a set—they all fail around the same time due to the M157's torque output. Right-side mount takes the worst abuse. 4-6 hours labor for all three mounts. Use OE or equivalent hydro mounts, not polyurethane.
Estimated cost: $1,800-3,000
Turbocharger Wastegate Rattle
Occasional · medium severity
Typical onset: 60,000-100,000 mi
Symptoms: Rattling sound from engine bay at idle or light throttle, 1500-2500 RPM, Sound disappears under boost or at higher RPM, No performance loss initially, Can progress to boost leak or turbo failure
Fix: Wastegate actuator arms wear and develop play in the bushings. Requires turbo removal to replace actuators or entire turbo assemblies. 12-16 hours labor per side if replacing turbos. Many owners live with the rattle if boost control is still normal, but it's an eventual failure point.
Estimated cost: $4,000-7,000 per turbo (often both done together)
Airmatic Suspension Strut Leaks
Occasional · medium severity
Typical onset: 70,000-110,000 mi
Symptoms: Vehicle sits low on one corner after sitting overnight, Compressor runs excessively—can hear it cycling frequently, 'Airmatic Suspension Malfunction' warning on dash, Visible oil residue on strut body
Fix: Replace failed air strut(s)—front or rear. Fronts tend to leak first. 2-3 hours per strut. Often one side fails, then the other follows within 10k miles due to increased compressor duty cycle. Some shops recommend doing both sides of an axle together to save comebacks.
Estimated cost: $1,500-2,200 per strut
Head Gasket Seepage (Not Catastrophic Failure)
Occasional · low severity
Typical onset: 80,000-120,000 mi
Symptoms: Slight coolant smell from engine bay, no visible leaks underneath, Minor coolant consumption—topping off every few thousand miles, Faint residue between head and block, visible only when inspecting closely, No overheating or mixing of fluids
Fix: The M157 can develop minor head gasket seepage at higher mileage, but it's usually a slow weep, not a blown gasket. If caught early and not overheating, some owners monitor and drive. Full head gasket job is engine-out, 30+ hours labor. Most techs recommend addressing if consumption exceeds 1 quart per 5k miles.
Estimated cost: $7,000-12,000 for both head gaskets
Fuel Injector Failure and Carbon Buildup
Occasional · medium severity
Typical onset: 60,000-100,000 mi
Symptoms: Rough idle or misfire codes on specific cylinders, Loss of power, hesitation on acceleration, Increased fuel consumption, Check engine light with P030X codes
Fix: Direct injection engines carbon up the intake valves and injectors can clog or fail. Walnut blasting intake valves takes 4-6 hours, injector replacement is 3-5 hours depending on how many are bad. Often one or two injectors go first, but if one fails, plan for others soon after. Top-tier fuel and occasional Italian tune-ups help but don't prevent.
Estimated cost: $1,200-2,000 for walnut blast, $800-1,500 per injector
Owner tips
Change oil every 5,000 miles with quality 0W-40 synthetic and send samples to Blackstone Labs starting at 40k miles—early bearing wear shows up in oil analysis before you hear it
Budget $3,000-5,000/year for maintenance and repairs after warranty expires—this is a $120k+ supercar in sedan clothing
Have a pre-purchase inspection by a Mercedes specialist focus on engine bearing noise during cold start—walk away if ANY knock is present
Keep the transmission cool—upgrade the trans cooler if you track or drive hard in hot climates, and address any cooler line seepage immediately
If the engine hasn't had bearings done by 60k miles, proactively replacing them is cheaper than a grenaded motor at 75k
Only buy if you have a $15k emergency fund for the inevitable bearing job or transmission cooler failure—this is a maintenance-intensive beast that rewards preparation and punishes neglect.
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.
Fitment notes: AGM battery required; located in trunk; high-performance application requires premium AGM specification
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Every control module on the 2011-2018 Mercedes-Benz CLS63 AMG — where it lives, replacement time, and what it takes to program a replacement. Modules marked dealer / factory tool won't work after a part swap alone — budget for programming.
Aftermarket tool coverage varies by software version and vehicle build — treat "aftermarket tool" rows as "usually possible" and verify against your tool maker's coverage list before promising a customer. Spot a wrong location or hour? Tell us — corrections ship fast here.
Size-standard part numbers — verify your connector type before buying. Rear blades are model-specific; check the package's vehicle list.
Fuel economy figures are EPA data via fueleconomy.gov (median across matching trims). Performance figures are compiled estimates for the 2018 Mercedes-Benz CLS63 AMG 5.5L V8 BiTurbo M157 and can vary by trim.
🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years and Jeff Moore · Master Lexus & Toyota Mechanic · 20+ years.