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Mercedes CLS550 Common Issues: The M278 V8 Four-Door Coupe Guide

Sun Feb 15 2026
Reliability Score: 65 /100

Common Failure Points & Costs

Component Failure Mileage Symptom Est. Cost (USD) Risk Level
Cylinder Scoring (Alusil Bores) 70k - 130k miles Rough idle, misfires, low compression (cylinders 5/1) $12,000 - $20,000 (Long Block Replacement) Critical
Timing Chain Tensioners 60k - 120k miles Cold-start rattle (3-5 seconds) $1,500 - $5,000 High
Airmatic Suspension Struts 60k - 90k miles Car sagging, 'Suspension Fault' warning $1,200 - $2,000 per corner High
Turbo Coolant Lines 60k - 100k miles Coolant loss, pink residue around turbos $800 - $1,500 High
Oil Cooler / Oil-Coolant Mixing 80k - 120k miles Milky coolant, metallic debris in oil $1,500 - $3,000 (Cooler) / $12,000+ (Long Block) Critical
COMAND / Electronics 50k - 80k miles COMAND freeze, camera failure, module faults $500 - $2,000 Medium

Reliability Verdict

The CLS550 (C218) with M278 V8 is a 402-449hp four-door coupe with the same cylinder scoring and timing chain tensioner flaws as all M278 engines. If you buy a 2015+ model with compression test and no cold-start rattle, it's a fantastic grand tourer. If not, you're gambling with a $20,000 long block replacement.

Mercedes CLS550 Common Issues: The $20,000 Used Four-Door Coupe Gamble

The Mercedes CLS550 (C218) with the M278 4.7L biturbo V8 is a 402-449hp four-door coupe that combines the elegance of a coupe with the practicality of a sedan.

But on the used market, it’s a maintenance nightmare. You can buy an $80,000 CLS550 for $20,000. Why? Because the cylinder bores score, the timing chain tensioners bleed down, and the Airmatic suspension leaks.

This guide breaks down exactly what fails on the C218 CLS550 with M278 V8.

1. CLS550 C218: Early vs Late Models

The CLS550 went through a facelift in 2015. You must understand the difference.

Early C218 CLS550 (2012-2014)

  • Engine: M278 4.7L biturbo V8 (402hp)
  • Risk Level: HIGH
  • Why: Early timing chain tensioners, higher cylinder scoring incidence.
  • Verdict: Buyable, but only with compression test and tensioner update verified.

Late C218 CLS550 (2015-2017)

  • Engine: M278 4.7L biturbo V8 (449hp)
  • Risk Level: MODERATE
  • Why: Updated tensioners with check valves, improved sealing, power bump to 449hp.
  • Verdict: The smart buy. Still has cylinder scoring risk, but lower tensioner failure rate.

2. Common Failures & Costs

A. Cylinder Scoring (The Existential Risk)

The CLS550 shares the same Alusil cylinder scoring flaw as all M278 engines. See our Mercedes M278 V8 Pillar Page for the full technical breakdown.

  • Symptom: Rough idle, misfires (cylinders 5/1), blue smoke.
  • Test: Compression test. All cylinders should show 150+ PSI. If cylinder 5 or 1 is below 140 PSI, walk away.
  • Cost: $12,000 - $20,000 for long block replacement.

[!WARNING] Critical: If the compression test shows low compression on cylinders 5 or 1, the car is a ticking time bomb. Walk away.

B. Airmatic Suspension

The CLS550 uses Airmatic air suspension. The air springs dry rot and leak.

  • Symptom: Car sagging on one corner, “Suspension Fault” warning.
  • Risk: The rubber air bags dry rot and leak, especially in cold climates.
  • Cost: $1,200 - $2,000 per corner (OEM). Arnott aftermarket struts are $700/corner.

C. COMAND & Electronics

The CLS550 has a complex COMAND system with cameras, sensors, and modules. These fail.

  • Symptom: COMAND freeze, camera failure, module faults, warning lights.
  • Mileage: 50,000 - 80,000 miles.
  • Fix: Module replacement or software update.
  • Cost: $500 - $2,000.

3. Maintenance Budget

Owning a CLS550 is not like owning a C-Class. It is a grand-tourer-level maintenance schedule.

  • Oil Changes: Every 5,000 miles (Mandatory). Mercedes’ 10,000-mile interval will accelerate cylinder scoring.
  • Tires: Rear tires last 15,000-20,000 miles. Expect $1,600/set.
  • Brakes: Large rotors. Expect $1,800/axle.

Annual Expectation: $4,500 - $6,000 in non-routine repairs.

4. The “Bargain” Trap

Scenario: You see a 2014 Mercedes CLS550 with 68k miles for $20,000. It looks clean.

Reality: It likely needs:

  1. Compression test verification (if scoring: $15,000)
  2. Timing chain tensioner update ($2,000)
  3. Turbo coolant lines ($1,200)
  4. Airmatic struts (2 corners: $3,000)

Total Immediate Cost: $6,200 (or $21,200 if cylinder scoring has occurred).

You have effectively doubled the price of the car in the first month.

5. Should You Buy One?

YES, IF:

  1. You are looking at a 2015+ model.
  2. You can afford a $5,000/year maintenance budget.
  3. You have a trusted Mercedes specialist nearby.
  4. You get compression test verification and clean cold-start test.

NO, IF:

  1. You are stretching your budget to buy the car.
  2. You rely on the dealer for service.
  3. You need 100% reliable transportation.
  4. You cannot afford a potential $20,000 long block replacement or $4,000 Airmatic repair.

6. Verdict

The Mercedes CLS550 (C218) with M278 V8 is a grand tourer bargain if you know what you’re doing. It offers 449hp, a glorious exhaust note, and the prestige of the three-pointed star for the price of a used Camry.

But it requires a “grand tourer” budget to keep running. If you go in with open eyes and a full wallet, it’s a rewarding experience. If you treat it like a Toyota, it will bankrupt you.

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Expert Buying Advice

Only buy a CLS550 M278 with: 1) Compression test (all cylinders 150+ PSI), 2) No cold-start rattle, 3) Airmatic function verified, 4) 2015+ model year preferred. Budget $4,500/year for maintenance.