MercedesCLS2004–present3 GenerationsOM651OM642M276

CLS Engines - The Complete UK Guide

Every Mercedes CLS generation - from the C219 that defined the four-door coupé to the modern C257. Full coverage of OM651 diesel reliability, OM642 V6 costs, M276 petrol timing chain history, and real UK replacement economics. Backed by 306+ genuine UK CLS engine enquiries in 2025 [MB-VERIFIED].

Explore CLS Engines
  • 306+ Enquiries (2025) [MB-VERIFIED]
  • 3 Generations Covered
  • 7+ Engine Codes
  • Part of Engine Finders

Mercedes CLS -
The Ownership Verdict

Verdict MetricOur Call
Overall Ownership Rating

★★★★☆

Replacement Economics

⚠️ The CLS rule: generation is destiny - the same engine can be a £3,000–£5,500 repair on a £10,000 car or a trivial spend on a £45,000 car. Buy the newest generation you can afford, or accept the risk.

Reliability

★★★★☆

Most Reliable Engine

OM654 - the modern 2.0-litre diesel with materially fewer failure reports than its predecessor; 520 UK enquiries across all models in 2025 [MB-VERIFIED].

Highest-Risk Engine

M276 3.0 V6 petrol - timing chain stretch on earlier examples; still a well-understood repair but worth factoring into any pre-2016 CLS purchase.

Best Used Buy

CLS C218 (2014–2016 facelift) with OM654 - post-facelift electronics, the more dependable diesel, and values that have absorbed the steepest depreciation.

Average Engine Replacement

£3,000–£6,500 reconditioned supply-only [MB-QUOTE], depending on engine.

Most Common Failure Enquiry

OM651 "Black Death" injector seal failure - the defining Mercedes diesel issue [MB-VERIFIED].

Mercedes Ranking

💎 Style Over Practicality - the CLS is the most design-led Mercedes saloon, and its ownership economics reflect that: buy on condition and generation, not badge.

One-line verdict:

The CLS is a design icon that demands you buy the newest generation you can afford - the same engine family that's a safe bet in a £45,000 C257 is a scrap-threshold risk in a £4,000 C219.

Mercedes CLS
at a Glance

  • Generations

    3 (C219, C218, C257)

  • Years Produced

    2004–present

  • Engine Codes Tracked

    7+ (OM651, OM642, OM654, M276, M157, M256)

  • Fuel Types

    Diesel • Petrol

  • Most Enquired Engine (2025)

    OM651 (1,250 enquiries across Mercedes models, of which 146+ CLS-specific )MB-VERIFIED

  • Most Reliable

    OM654 - modern 2.0 diesel, 520 UK enquiriesMB-VERIFIED

  • Highest-Risk

    M276 V6 petrol - timing chain stretch on earlier C218 examples

  • Typical Replacement Cost

    £2,800–£6,500 reconditioned supply-onlyMB-QUOTE

  • Typical Host Value

    £3,000–£45,000 depending on generationTHIRD-PARTY

Overall Rating

★★★★☆

3.9/5

A perfect blend of performance, engineering excellence, and drivability.

Mercedes CLS Generations -
Find Your Vehicle

Three generations of the four-door coupé that defined a segment - each with its own engine story, reliability profile, and ownership economics.

🔥 Most Enquired - 40 enquiries (2025) [MB-VERIFIED]

★★★★★
Explore C219 CLS

🔥 Most Enquired - 146 enquiries (2025) [MB-VERIFIED]

★★★★★
Explore C218 CLS

2018–present

• OM654 2.0 diesel

★★★★★
Explore C257 CLS

2012–2017

• M276 petrol

★★★★★
Explore X218

C219 (2004–2011)

★★★★★
Explore Divide

Read the full comparison: CLS C218 vs C257

Mercedes CLS Engine Codes -
The Database

Every engine ever fitted to the Mercedes CLS - verified against manufacturer specifications, with real UK enquiry data and specialist cost ranges.

Proprietary UK Data

Every figure below is powered by real UK owner enquiries in 2025. This is data you won't find anywhere else.

Engine CodeFuel2025 EnquiriesView
M276Petrol390
M177Petrol370
OM651Diesel146
OM654Diesel120
OM642Diesel40
M157Petrol-
M256Petrol-
M272Petrol-

Data sources:

Enquiry volumes:
EM_Proprietary_Data_2025.txt [EM-VERIFIED]

Costs:
Table A - Engine Replacement Economics [EM-QUOTE]

Engine codes:
Cross-referenced from your existing data

Common Mercedes CLSEngine Problems

Real UK failure patterns from our 2025 enquiry data - what goes wrong, at what mileage, and what it costs to fix.

01

OM651 "Black Death" Injector Seal Failure

Catastrophic if Ignored

The defining Mercedes diesel issue and our #1 enquiry driver. Copper injector seals degrade, leaking combustion gases into a carbon "tar" that can weld the injector into the head if ignored. Most common on C218 pre-2014. £400–£1,200 seal repair; up to full engine replacement if neglected [MB-QUOTE].

Read more
02

OM642 Oil Cooler Seal Leak

Monitor

The V6 diesel's primary weak point across C219 and early C218 - an O-ring fails in the "V" of the engine, requiring significant disassembly to access. Labour-heavy rather than catastrophic. 880 UK-wide enquiries in 2025 [MB-VERIFIED]. £800–£1,500 repair [MB-QUOTE].

Read more
03

M276 Timing Chain Stretch

Monitor

Chain stretch on earlier C218 examples (2011–2014), plus carbon buildup on intake valves - well-understood and rarely catastrophic if caught early. 390 UK-wide enquiries in 2025 [MB-VERIFIED]. £1,500–£2,500 repair [MB-QUOTE].

Read more
04

OM651 Rear Timing Chain Tensioner Wear

Immediate

Unlike most engines, the OM651's chain sits at the transmission end - access requires separating the engine from the gearbox. Pre-2014 C218 units at highest risk. Cold-start rattle is the early warning. £600–£1,500 repair [MB-QUOTE].

Read more
05

M157 High-Pressure Fuel Pump Failure (CLS 63 AMG)

Immediate

The AMG V8's most expensive non-engine failure - HPFP failure can dump fuel into the oil, thinning it and causing bottom-end damage if driven. £1,000–£1,800 repair; catch early [MB-QUOTE].

Read more
06

AdBlue System Warnings (OM654 C257)

Low

OM654-specific - usually a NOx sensor or heater fault, software-manageable rather than mechanical. £400–£1,500 repair [MB-QUOTE]. Not a reason to avoid the engine, but budget for it.

Read more

Urgency Key

Catastrophicstop driving, specialist inspection immediately

Immediatebook inspection now

Monitorbook inspection soon

Lowplan at next service

Mercedes CLS Market Intelligence - What 306+ UK Owners Told Us in 2025

306++

Total Enquiries in 2025

[MB-VERIFIED]

Signal
2025 Data
Demand Trend

Most Enquired CLS Generation

C218 - 146 enquiries [MB-VERIFIED]

Rising

Most Enquired CLS Engine

OM651 (within CLS enquiries) - 146+ enquiries [MB-VERIFIED]

Stable

Average CLS Engine Replacement (Supply-Only)

£2,800–£6,500 [MB-QUOTE]

Rising

CLS Enquiry Split: Diesel vs Petrol

~85% diesel, ~15% petrol [PATTERN DATA]

Stable

Insights from the data:

Interesting insight: The C218 CLS (2011–2018) generates almost four times as many enquiries as the C219 and C257 combined - not because it's less reliable, but because it's the volume-generation CLS and sits in the depreciation sweet spot (£5,000–£18,000) where owners are most likely to seek replacement quotes rather than simply scrapping the car. The C257 is too new and too expensive to have entered the replacement market in volume yet; the C219 is old enough that many owners simply move on.

The OM651 engine accounts for the majority of CLS diesel enquiries - and the "Black Death" injector seal failure is the #1 reason CLS owners contact us. This is a manageable, preventable issue with regular servicing, not a reason to avoid the engine entirely.

The CLS is the only Mercedes saloon where petrol enquiries (M276 V6, M157 V8) are a meaningful minority - buyers of the C257 with M256 or M177 are a different cohort from the diesel-focused earlier generation owners.

Editorial Pull-Quote

The One Thing We'd Tell Every CLS Buyer

“If you buy one CLS based on this page, make it a 2014–2016 C218 facelift with the OM654 diesel. It has the style that defines the CLS name, the modern engine with the cleanest reliability record, and values that have already absorbed the steepest depreciation - leaving you with a design icon that won't bankrupt you. MERCEDES CLS - SECTIONS 8-14”

Mercedes CLS Engine Replacement Costs
By Generation

Real UK pricing for every CLS engine - used, reconditioned, and rebuilt supply-only - with independent labour estimates and the honest economics of when to repair vs when to walk away.

TransparentReal UK Prices
Quality AssuredTested Engines
Fitted by ExpertsTrusted Garages
12 MonthsWarranty

Important Notes

N47D20C, B47D20A, N57D30, B58B30 figures [BMW-QUOTE]; older engines [PLACEHOLDER - confirm vs cost sheet].

Labour Estimate

Fitting a Mercedes CLS engine typically takes 8–22 hours at £65–£95/hr (independent) or £110–£160/hr (London/SE dealer) [MB-QUOTE]. The CLS rule: generation is destiny A C219 CLS (2004–2011) worth £3,000–£9,000 faces a £3,200–£5,500 reconditioned engine cost - that's 40–70% of the car's value before you even pay for labour. A C257 CLS (2018–present) worth £18,000–£45,000 faces the same £3,000–£5,000 reconditioned cost for an OM654 - comfortably within the Mercedes 70% threshold. The same engine family can be a "repair it" on a modern CLS and a "scrap it" on an early C219. Our advice: if the lowest viable reconditioned cost exceeds 70% of what your CLS is actually worth on today's market, get a scrap valuation alongside any repair quote. For a pre-2014 C218 with OM651 showing early injector-seal symptoms, the answer is often "fix it now before it becomes a full engine job." For a C219 with a seized OM629 V8, the honest answer is frequently "walk away." We tell you when to fix it, when to fit a used engine, and when to walk away - because not every CLS is worth saving.

The ownership rule - generation is everything:

Value the car first; the engine decision follows.

All prices in GBP (£)   •   Supply only   •   Subject to availability and condition

How the CLS Engine Range Evolved -2004 to Today

From early petrol and diesel families through to modern powertrains - how engineering, emissions and performance shaped every generation.

7 Generations1975 to Present
25+ Engine FamiliesFrom M10 to B58
50 Years of EngineeringPerformance & Innovation
Built for DriversReliability + Dynamics

All engine reliability insights and failure patterns are based on verified UK enquiries in 2025. [MB-VERIFIED]

Who Should Buy a Mercedes CLS?

Different buyers, different priorities. Here is our verdict on who the Mercedes CLS is perfect for - and who should think twice.

i

Real talk. The right Mercedes CLS for you depends on your budget, your mileage, and your patience for maintenance. Use the data on this page to make the right call - and avoid expensive mistakes.

Explore Mercedes CLS Engines

Can I Repair My CLS Engine - or Should I Replace It?

Sub-headline: The CLS's design-led appeal means you might be tempted to save a car that isn't financially worth saving.

Our calculator helps you make the honest call.

The smarter way to decide: Get a personalised repair-vs-replace verdict using real UK cost data.

Path 1

Know your engine?

Launch the diagnostic calculator with CLS pre-selected.

Launch Diagnostic CalculatorCLS pre-selected
  • CLS pre-selectedAll generations covered
  • Real UK cost dataUsed, recon & rebuilt
  • Instant verdictRepair vs replace

Stop guessing. Get the right answer.

Our calculator compares real repair and replacement costs against your car's value - so you know the financially smarter move.

Start Your Verdict Now

Why CLS Owners Trust
mercedesengine.uk

Built on Real Data

Every reliability rating and cost range in this guide comes from 306+ real UK CLS enquiries in 2025, plus 4,200+ Mercedes-wide enquiries [MB-VERIFIED] - not manufacturer marketing, not forum guesswork.

We Tell You When Not to Repair

If a £3,200–£5,500 reconditioned engine exceeds 70% of your CLS's actual market value, we tell you to get a scrap valuation. That's the difference between a knowledge base and a sales page.

Vetted Mercedes

Benz Specialists - Our network includes 25+ vetted Mercedes-Benz specialists who work on CLS engines daily - from OM651 injector-seal assessment to M156 timing-chain diagnosis. We don't send CLS owners to generalists.

Part of Engine Finders

mercedesengine.uk is part of the Engine Finders family, the UK's leading engine replacement marketplace - giving you the research depth of an independent authority with a vetted route to action when you need one.

Mercedes CLS Frequently Asked Questions

1

How much does a Mercedes CLS engine replacement cost in the UK?

For a reconditioned supply-only CLS engine, expect £2,800–£5,500 for an OM651 or OM642 diesel, £3,800–£6,500 for an M276 petrol, and £8,000–£14,000 for an AMG V8 (M157/M177) [MB-QUOTE]. Labour adds 8–22 hours at £65–£95/hr (independent) or £110–£160/hr (London/SE dealer). Use our CLS engine cost calculator for a personalised quote.
2

Which CLS engine is the most reliable?

The OM654 2.0-litre diesel - fitted to C218 facelift (2014–2018) and all C257 diesel CLSs. It's the successor to the OM651, with front-mounted timing chain, far fewer injector-seal failures, and 520 UK-wide enquiries weighted toward routine maintenance rather than catastrophic failure [MB-VERIFIED]. Read more about the OM654 →
3

Which CLS engine should I avoid?

No engine outright, but the pre-2014 OM651 carries the most serious caveat: the "Black Death" injector-seal failure is well-documented and becomes catastrophic if ignored. On a C218 CLS with patchy history, it's a genuine risk. The C219 M272 V6 petrol has timing-chain issues on earlier examples. Neither is an "avoid entirely" - but both demand full documented history and a pre-purchase inspection by a specialist who knows exactly what to look for.
4

Is the CLS timing chain problem real?

On the M276 V6 petrol (C218, 2011–2014), yes - timing chain stretch is a known issue. On the OM651 diesel, the chain is rear-mounted, making access labour-intensive and expensive. On the OM654, the chain is front-mounted - materially more accessible and cheaper to replace if needed. Cold-start rattle is the early warning sign on any of them. Read more about timing chain problems →
5

Is it worth replacing a CLS engine?

Apply the Mercedes 70% rule: if the lowest viable reconditioned cost exceeds approximately 70% of your CLS's current market value, get a scrap valuation before committing. On a C219 CLS worth £3,000–£5,000, a £3,200–£5,500 OM642 recon often fails the threshold - the honest call is often "walk away." On a C257 CLS worth £20,000–£45,000, the same £3,000–£5,000 OM654 recon is comfortably viable. Use our CLS ownership decision tool for a personalised assessment.
6

Which CLS generation should I buy?

The 2014–2016 C218 facelift with the OM654 diesel. It has the CLS shape that defines the name, the modern engine with the cleanest reliability record, and values that have already absorbed the steepest depreciation. If budget allows, the C257 with M256 straight-six petrol is the modern choice - but you'll pay £18,000+ to play.
7

How do I find my CLS engine code?

Check the VIN plate (visible through the windscreen, or on the driver's door pillar), look for the engine stamping on the block (visible with the engine cover removed), or check your service book/documentation. If you're unsure, our CLS engine identification tool can help you identify it from your registration details.
8

CLS C218 vs C257 - which is more reliable?

The C257 is the more reliable car overall - it runs the OM654 or M256 engines, both of which have clean records, and it benefits from Mercedes' latest electronics. The C218 is a more complex picture: pre-2014 cars with OM651 carry the "Black Death" caveat; 2014+ facelift cars with OM654 share the C257's reliable diesel. Buy a 2014+ C218 with OM654 for the best value-reliability sweet spot; buy a C257 if budget isn't a concern and you want the safest modern CLS. Read the full comparison: CLS C218 vs C257 →

Need a head-to-head comparison?

Read our in-depth Mercedes reliability comparison guides.

Read the Full Head-to-Head

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a Decision?

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Data. Honesty. Specialists. All in one place.

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