2018 MERCEDES-BENZ CLS63 AMG

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

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

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

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)

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

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

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