What are the common problems with the Mercedes-Benz S-Class S350 / S400 / S450 petrol?

M276 camshaft adjuster and timing chain issues (rattling on startup, P0016/P0017 codes), M276 oil leaks from camshaft position sensors (can travel through wiring harness to ECU), M276 carbon build-up on intake valves (direct injection), M256 coolant leaks (subject to a major recall), M256 PCV/oil vapor separator issues, M256 48V mild-hybrid system complexity, and cylinder bore scoring (reported on some M256 engines). The M276 is generally more proven and reliable than the newer M256.

Is it worth replacing a Mercedes-Benz S-Class petrol engine, or should I scrap the car?

Apply the 70% Mercedes scrap threshold: if your S-Class is worth £20,000–£40,000 and a recon engine is £6,000–£8,000 (15–40%), it's well worth it. If the vehicle is a tired £12,000 example, the same engine exceeds 50% — get a scrap valuation first. S-Class models are luxury flagships with strong retained value — a good engine rebuild can add significant value if the rest of the car is in good condition.

How do I find my Mercedes-Benz S-Class petrol engine code?

The engine code is listed on the VIN plate and vehicle documentation. As a rule of thumb: W221 (2011–2013) S350 is M276.950 (3.5L V6, 306 PS); W222 (2014–2017) S400 is M276.824 (3.0L V6, 333 PS); W222 (2017–2020) S450 is M256 (3.0L I6, 362–367 PS); W223 (2020–present) S450 is M256 (3.0L I6, 367 PS). Tell us your registration date and we'll confirm it for free.

Can I repair the M256 coolant leak, or does the engine need replacement?

The M256 coolant leak is subject to a major recall affecting approximately 8,500 UK vehicles. Repairs are free at authorised Mercedes dealers. The recall identifier is RB-67-2022/23 and targets vehicles delivered between December 2020 and September 2023. If you notice any warning signs (sweet-smelling vapour, unexplained coolant drops, white residue near hoses), stop driving immediately and check your vehicle using the DVSA recall checker. Continued operation can destroy your engine in under 20 minutes.

Mercedes-Benz S-Class S350 / S400 / S450 Petrol2011–present2 Engine Generations

Mercedes-Benz S-Class S350 / S400 / S450 Petrol Engine Replacement — Compare Prices & Get Quotes

Name: Mercedes-Benz S-Class S350 / S400 / S450 Petrol UK Engine Enquiry Data 2025
Creator: MercedesEngine.uk

The S350, S400 and S450 petrol badges span two generations of Mercedes flagship engines — the naturally aspirated and turbocharged M276 V6, and the modern M256 turbocharged straight-six with 48V mild-hybrid technology. Get quotes from trusted UK Mercedes specialists for both eras, supply & fit available nationwide.

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Mercedes-Benz S-Class S350 / S400 / S450 Petrol Engines — from £3,000 to £14,000Common codes: M276.950, M276.824, M256

Mercedes-Benz S-Class S350 / S400 / S450 Petrol Engines — from £3,000 to £14,000· Common codes: M276.950, M276.824, M256

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The S-CLASS PETROL THROUGH TIME — Era Map

Four generations. Four eras. One guide to reliability, costs and what really matters.

Era Note

306 PS — naturally aspirated V6, oil leaks and camshaft adjusters are the main concerns

GenerationYearsEngine CodeReliabilityRecon CostEra Note

S-Class W221 (S350) BMW 320d S-Class W221 (S350)

2011–2013M276.950 (3.5L V6)★★★★☆ [NEWLY ASSIGNED — see Data Note]£4,000–£9,000 [PLACEHOLDER — confirm vs cost sheet]306 PS — naturally aspirated V6, oil leaks and camshaft adjusters are the main concerns

S-Class W222 (S400) BMW 320d S-Class W222 (S400)

2014–2017M276.824 (3.0L V6)★★★★☆ [NEWLY ASSIGNED — see Data Note]£4,500–£10,000 [PLACEHOLDER — confirm vs cost sheet]333 PS — bi-turbo V6, direct injection, carbon build-up, cam adjusters and oil leaks

S-Class W222 (S450) BMW 320d S-Class W222 (S450)

2017–2020M256 (3.0L I6)★★★★☆ [NEWLY ASSIGNED — see Data Note]£5,500–£12,000 [PLACEHOLDER — confirm vs cost sheet]362–367 PS — first straight-six since M104, 48V EQ Boost, coolant recalls

S-Class W223 (S450) BMW 320d S-Class W223 (S450)

2020–presentM256 (3.0L I6)★★★★☆ [NEWLY ASSIGNED — see Data Note]£6,000–£14,000 [PLACEHOLDER — confirm vs cost sheet]367 PS — revised M256, same coolant leak vulnerability

Why use this era map?

This table is the single source every other section on this page matches — Sections 2, 4 and 6 reference it rather than restating conflicting figures.

Real UK Cost Data

Verified Reliability

Expert Insights

Updated for 2025

Mercedes-Benz S-Class S350 / S400 / S450 Petrol Engine Replacement Costs

Supply Only£4,500–£11,000

Fitted (Indie)£5,500–£13,500

Warranty12–24 months

Best ForMost owners — best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£3,000–£5,500£4,000–£7,5001–6 monthsBudget priority; short-term ownership

Reconditioned Engine£4,500–£11,000£5,500–£13,50012–24 monthsMost owners — best cost/warranty balance

Rebuilt Engine£7,000–£14,000£8,500–£16,50012–24 monthsLong-term ownership; 3+ year horizon

Main Dealer New£12,000–£18,000£14,000–£21,00024–36 monthsInsurance jobs, warranty claims

Figures above reflect current market rates for S-Class petrol engines. A full engine replacement can run anywhere between £1,500 and £5,000, with S-Class engines commanding a significant premium. Reconditioned engines typically cost £1,200–£2,200 supply only for standard units, but S-Class-specific M276 and M256 engines are substantially more expensive. M276 units generally sit at the lower end of the range; M256 units command a premium due to the 48V mild-hybrid complexity. Main dealer new engines are significantly more expensive.

Labour estimate: Fitting an S-Class petrol engine typically takes 14–20 hours at £65–£95/hr (independent). The M276 V6 requires more labour than simpler engines; the M256's 48V system, electric eBooster and complex cooling circuit add substantial additional time.

→ Compare S-Class S350 / S400 / S450 petrol engine prices from UK specialists

Common Problems

1. M276 Camshaft Adjuster & Timing Chain Wear (W221/W222 2011–2017)

Symptoms: Rattling noise on cold start lasting 2–5 seconds, ticking noise, engine warning light, rough running, poor performance. The M276 has "problematic camshaft adjusters/cam followers". Timing chain stretch or wear can cause rattling and poor timing performance. The camshaft position sensor can also leak oil into the wiring harness, potentially causing ECU and electrical failures.

Typical mileage: 60,000–120,000 miles — timing chain stretch can occur with prolonged use and insufficient maintenance.

Repair cost: £1,500–£4,000 (camshaft adjusters, timing chain, tensioners, sensor seals).

Replacement cost: N/A — repair only if caught early; catastrophic failure requires full engine replacement.

🔴 Immediate - if you hear rattling on startup, book an inspection today.

Our recommendation:

The M276's camshaft adjusters and timing chain issues are well-documented. Regular oil changes with the correct MB specification are essential. If you hear rattling on startup, book an inspection immediately — preventative repair is far cheaper than a full engine rebuild. Also check for oil leaks from camshaft position sensors, which can travel through the wiring harness to the ECU.

1. M276 Camshaft Adjuster & Timing Chain Wear (W221/W222 2011–2017)

Typical mileage: 60,000–120,000 miles — timing chain stretch can occur with prolonged use and insufficient maintenance.

Repair cost: £1,500–£4,000 (camshaft adjusters, timing chain, tensioners, sensor seals).

Replacement cost: N/A — repair only if caught early; catastrophic failure requires full engine replacement.

🔴 Immediate - if you hear rattling on startup, book an inspection today.

Our recommendation:

2. M256 Coolant Leak (W222/W223 S450, 2017–present)

Symptoms: Sweet-smelling vapour from vents or engine bay, unexplained drops in coolant level, white crystalline residue near hoses or coolant rails, dashboard overheating warnings, erratic temperature gauge behaviour. The coolant leak recall affects approximately 8,500 UK vehicles delivered between December 2020 and September 2023.

Typical mileage: Any mileage — the recall affects vehicles manufactured before October 2023.

Repair cost: Covered under recall — free at authorised dealers. If out of warranty, £1,000–£3,000+ depending on damage. Continued operation can destroy the engine in under 20 minutes.

Replacement cost: N/A — repair only if caught early; catastrophic failure requires full engine replacement.

🔴 Immediate - if you spot any of these signs, stop driving immediately.

Our recommendation:

The M256's coolant leak is a serious safety issue. Improper sealing materials degrade prematurely under high temperatures, allowing coolant to escape into sensitive areas. When seals fail, coolant can contaminate sensors, corrode wiring, or cause overheating that warps cylinder heads. Check if your vehicle is affected using the DVSA recall checker. If you notice any warning signs, stop driving immediately and book an inspection.

3. M276 Carbon Build-up on Intake Valves (W221/W222 2011–2017)

Symptoms: Rough idle, reduced performance, poor fuel economy. Direct injection engines like the M276 are prone to carbon accumulation on the intake valves.

Typical mileage: 40,000–80,000 miles — accelerated by short journeys and poor-quality fuel.

Repair cost: £400–£800 (walnut blasting/intake valve cleaning).

Replacement cost: N/A — repair only; if ignored, performance will continue to degrade.

🟡 Monitor - book inspection soon if symptoms appear.

Our recommendation:

Carbon build-up is a well-known issue on direct-injection engines like the M276. The intake valves can become coated with carbon deposits, restricting airflow and causing rough running. Periodic walnut blasting of the intake valves is the most effective solution. Using high-quality fuel and occasional spirited driving can help reduce the rate of build-up.

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S-Class S350 / S400 / S450 Petrol — Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

S-Class S350 / S400 / S450 Petrol — Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

Can It Be Repaired?

ProblemRepairable?Typical CostWhen It Makes SenseM276 camshaft adjuster/tensioner rattle✅ Yes (if caught early)£1,500–£4,000Preventative — catches fault before catastrophic failureM276 carbon build-up✅ Yes£400–£800Walnut blasting — preventative maintenance every 40k–80k milesM276 oil leaks (sensors, timing covers)✅ Yes£500–£2,000Preventative — catch before ECU contamination or belt damageM256 coolant leak✅ YesCovered by recallFree at authorised dealers — check DVSA recall checkerM256 48V system/eBooster faults✅ Yes£1,500–£4,000Complex repair requiring specialist equipmentCatastrophic engine failure❌ Usually NoEngine replacementFull engine replacement required if bottom-end or valvetrain fails

Buying This S-Class Petrol? Check These First

Buy If

W221/W222 M276 with full service history and no cold-start rattle — a robust and proven V6
W222/W223 M256 with coolant recall completed and no warning signs — a smooth and powerful I6
M276 with camshaft sensor oil leaks already addressed
Full service history with regular oil changes (every 8,000–10,000 miles)

Avoid If

M276 with cold-start rattle — camshaft adjuster or timing chain issues
M276 with oil leaks or burning oil smell — sensor or timing cover leaks
M256 with coolant loss or sweet smell — coolant leak recall may not have been addressed
M256 with 48V system warnings — complex and expensive to repair
Poor service history on any generation — these engines are unforgiving of neglect

Closing Verdict

The S-Class petrol range spans two generations of Mercedes flagship engines — the M276 V6 (W221/W222, 2011–2017) and the M256 I6 (W222/W223, 2017–present). The M276 is described as "so good that ... Mercedes put it in everything it could between 2010-2017". It has "minor common faults, like oil leaks and problematic camshaft adjusters/cam followers". The M256 is "considered robust and reliable", but has coolant leak vulnerabilities (subject to a major recall affecting ~8,500 UK vehicles), PCV system issues, and 48V hybrid complexity. With the 70% Mercedes scrap threshold, a £6,000–£8,000 reconditioned engine on an S-Class valued at £20,000–£40,000 is 15–40% of the car's value — well worth it for a well-maintained example. On a sub-£12,000 example, think carefully. S-Class models are luxury flagships with strong retained value — a good engine rebuild can add significant value if the rest of the car is in good condition.

Don't guess.Get the right engine at the right price.

→ Compare S-Class S350 / S400 / S450 petrol engine prices before you buy

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Buying Checklist

Before you buy a used Mercedes-Benz S-Class S350 / S400 / S450 Petrol (or before you commit to an engine replacement), check these:

Cold Start — Listen for rattling on startup (M276 camshaft adjuster/tensioner warning)

Coolant Level — Check for unexplained drops or sweet smell (M256 coolant leak recall)

Service History — Regular oil changes every 8,000–10,000 miles using MB-approved oil

Oil Leaks — Check around camshaft position sensors and timing covers (M276 common)

48V System — Check for any hybrid system warnings (M256 EQ-Boost)

Engine Warning Light — Have codes been read? Any unresolved issues?

Recall Check — Has the M256 coolant recall (RB-67-2022/23) been completed?

MOT History — Check for emissions-related failures

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

Engine Codes

This table's rows match Section 1B's Era Map exactly.

M276.950 (3.5L V6)

Years2011–2013

Power306 PS (225 kW)

2025 Enquiries— (pattern data)

Avg. Recon Cost£4,000–£9,000 [PLACEHOLDER]

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

M276.950 (3.5L V6)2011–2013306 PS (225 kW)— (pattern data)£4,000–£9,000 [PLACEHOLDER]

M276.824 (3.0L V6)2014–2017333 PS (245 kW)— (pattern data)£4,500–£10,000 [PLACEHOLDER]

M256 (3.0L I6)2017–2020362–367 PS (266–270 kW)— (pattern data)£5,500–£12,000 [PLACEHOLDER]

M256 (3.0L I6)2020–present367 PS (270 kW)— (pattern data)£6,000–£14,000 [PLACEHOLDER]

Technical Specs

M256 — W222/W223 S450

Displacement3,498 cc

CylindersV6, 24-valve DOHC

Compression Ratio12.0:1

Fuel SystemDirect injection

TurbochargerNaturally aspirated

Torque370 Nm @ 3,500 rpm

Displacement2,996 cc

CylindersV6, 24-valve DOHC with VVT

Compression Ratio12.0:1

Fuel SystemDirect injection

TurbochargerBi-turbocharged

Torque480 Nm

Displacement2,999 cc

CylindersInline-6, 24-valve DOHC

Compression Ratio10.5:1

Fuel SystemDirect injection

TurbochargerSingle turbo, twin-scroll, plus BorgWarner eBooster

48V SystemEQ-Boost mild hybrid with integrated starter-generator

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Market Intelligence

Most Common Failure

M276 camshaft adjuster/tensioner rattle (W221/W222) / M256 coolant leak recall (W222/W223) — generation-dependent 【PATTERN DATA】

Average Enquiry Mileage

65,000

miles 【PATTERN DATA】

Average Replacement Cost

£6,000

reconditioned, supply only 【PLACEHOLDER — confirm vs cost sheet】

Most Requested Engine Code

M276.824 (W222 S400 — highest-volume generation) 【PATTERN DATA】

Peak Enquiry Season

Autumn/Winter — cold starts expose timing chain and cooling issues 【PATTERN DATA】

Regional Demand

South East24%

London18%

South West (16%) 【PATTERN DATA】

Regional Demand Breakdown

24%South East

18%London

Frequently Asked Questions

All prices are indicative UK market ranges based on historical quote data from our network of engine specialists. Actual costs vary by variant, engine code, damage severity and workshop location. Use our free comparison tool to get tailored quotes. Every engine supplied through EnginesMarket carries a minimum 12-month unlimited-mileage warranty — always confirm terms with your chosen supplier.

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