Mercedes Benz S Class 350/450 Petrol Engine ReplacementCompare Prices & Get Quotes
Get quotes today from trusted UK Mercedes Benz S Class 350 and 450 petrol engine specialists. Compare prices on reconditioned, rebuilt and used engines for the 3.5-litre V6 and the 3.0-litre mild-hybrid inline-six - supply & fit available nationwide.
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12-Month Warranty
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100+ Suppliers
From £2,800 to £5,400
Used from £1,500 · Reconditioned from £2,800 · Common codes: M276.950, M276.952, M256.930
From £1,500
Tested, bare/short engine
From £2,800
Rod bearings addressed, tested
From quote
Upgraded bearings, full teardown, revised valvetrain
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3 Simple Steps3 Simple Stepsto Finding the Best Mercedes Benz S Class 350/450 Petrol Replacement Engineto Finding the Best Mercedes Benz S Class 350/450 Petrol Replacement Engine
Most replacements completed within 3-5 days.
Variant HistoryMercedes Benz S Class 350/450 Petrol - Engine History & Specs at a Glance
The S 350 debuted with the W221 generation in 2011 as a mid-cycle upgrade, powered by the M276 3.5-litre V6 petrol producing 306hp - a significant leap over the previous M272 unit. This naturally aspirated V6 featured BlueDIRECT direct injection and MSI multi-spark ignition for improved efficiency and power. In 2020, the W223 S 450 introduced the M256 3.0-litre inline-six with 48V EQ Boost mild-hybrid technology, delivering 367hp and representing a major shift toward electrified flagship mobility.
Variant HistoryMercedes Benz S Class 350/450 Petrol - Engine History & Specs at a Glance
The S 350 debuted with the W221 generation in 2011 as a mid-cycle upgrade, powered by the M276 3.5-litre V6 petrol producing 306hp - a significant leap over the previous M272 unit. This naturally aspirated V6 featured BlueDIRECT direct injection and MSI multi-spark ignition for improved efficiency and power. In 2020, the W223 S 450 introduced the M256 3.0-litre inline-six with 48V EQ Boost mild-hybrid technology, delivering 367hp and representing a major shift toward electrified flagship mobility.
Mercedes Benz S Class 350/450 Petrol
Fuel TypePetrol (M276: naturally aspirated V6; M256: turbocharged inline-six with 48V MHEV)
Engine Size Range3.0L-3.5L (M276: 3,498cc; M256: 2,999cc)
Power Output Range306-367hp across the variant's historyEngine History Timeline
M276.950 3.5L naturally aspirated V6, 306hp @ 6,500rpm (S 350, W221 facelift)
2017 - M276.952 3.0L twin-turbo V6, S 450 (W222, certain markets)
M256.930 3.0L turbocharged inline-six with 48V EQ Boost, 367hp (S 450, W223)
Key Specs Snapshot
Fuel TypePetrol (M276: naturally aspirated V6; M256: turbocharged inline-six with 48V MHEV)Engine Size Range3.0L-3.5L (M276: 3,498cc; M256: 2,999cc)Power Output Range306-367hp across the variant's historyYears Produced2011-presentEvery engine fitted to the Mercedes Benz S Class 350 and 450 petrol is covered below, with UK rebuilt pricing and known failure points - from M276 timing chain rattle to M256 wiring harness degradation and 48V system issues.
Mercedes Benz S Class 350/450 Petrol Engine Codes - Specifications & Replacement CostMercedes Benz S Class 350/450 Petrol Engine Codes - Specifications & Replacement Cost
3.5L Naturally Aspirated V6 (2011-2013)
Power Output306 hp (225 kW) @ 6,500 rpmTorque370 Nm (37.8 kgm) @ 3,500-5,250 rpmYears Fitted2011-2013Displacement3,498 ccCylindersV6, 60° V-angle, DOHC, 24-valveEngine CodeM 276.950
Compatible Trim Levels
- S 350
- S 350 4MATIC
- S 350 BlueEFFICIENCY (W221, W222)
Find your exact engine code, specs and UK replacement cost guide.
Used
Tested, ready-to-fit engine
£1,500-£2,500
Reconditioned
Addressed known issues, tested
£2,800-£3,800
Rebuilt
Full teardown, upgraded internals
£3,200-£4,500
Common Failure
Timing chain tensioner wear causing cold-start rattle - the M276 V6 has hydraulic secondary chain tensioners that can leak oil pressure, causing a metallic rattle on startup. M276 engines with engine numbers below a certain threshold may require updated tensioners and check valves per Mercedes TSB LI05.10-P-056435. Oil cooler seal degradation and coolant leaks from hoses are also common.
The S 350's M276 V6 and the S 450's M256 inline-six are among Mercedes' most refined petrol engines, but both have well-documented weaknesses that can lead to significant repair costs. The M276 suffers from timing chain tensioner wear and oil cooler seal degradation, while the M256 can develop wiring harness issues and 48V system faults. Every rebuilt engine supplied through EnginesMarket includes upgraded components addressing these original failure points, plus a minimum 12-month unlimited-mileage warranty.
The S 350's Signature Weakness
Affected Vehicles
Mercedes S 350 (M276.950, 2011-2013)
Typical Failure Mileage
60,000-100,000 miles
Root Cause
The M276's hydraulic secondary chain tensioners can lose oil pressure over time, causing a metallic rattling noise on cold starts. The tensioners have a weak spring and rely on oil pressure to maintain tension. Mercedes issued TSB LI05.10-P-056435 covering updated tensioners and check valves.
Why It Happens
The M276's hydraulic secondary chain tensioners can lose oil pressure over time, causing a metallic rattling noise on cold starts. The tensioners have a weak spring and rely on oil pressure to maintain tension. Mercedes issued TSB LI05.10-P-056435 covering updated tensioners and check valves.
Dealer (parts + labour)
£1,000-£1,800
Specialist (parts + labour)
£700-£1,200
What it involves
Replace hydraulic tensioners, install check valves per TSB
Suitability
Effective if caught early when rattle first appears
1 - 2 daysDealer (parts + labour)
£2,500-£4,000
Specialist (parts + labour)
£1,800-£2,800
What it involves
Replace timing chains, tensioners, guides, camshaft sprockets
Suitability
If rattle has persisted and chain stretch is confirmed
1 - 2 daysDealer (parts + labour)
£5,000-£7,500
Specialist (parts + labour)
£3,200-£4,500
What it involves
Complete engine swap with upgraded tensioners and timing components, 12-month warranty
Suitability
If timing failure has caused valve damage
1 - 2 daysAll prices are indicative UK market ranges based on current UK specialist supplier data.| Repair Tier | Dealer (Parts + Labour) | Specialist (Parts + Labour) | What It Involves | Suitability | Estimated Time |
|---|---|---|---|---|---|
 Preventative - Timing chain tensioner replacement Minor | £1,000-£1,800 | £700-£1,200 | Replace hydraulic tensioners, install check valves per TSB | Effective if caught early when rattle first appears | 1 - 2 days |
 Intermediate - Full timing chain kit Best Value | £2,500-£4,000 | £1,800-£2,800 | Replace timing chains, tensioners, guides, camshaft sprockets | If rattle has persisted and chain stretch is confirmed | 1 - 2 days |
Full Replacement - Rebuilt M276 engine Best Value | £5,000-£7,500 | £3,200-£4,500 | Complete engine swap with upgraded tensioners and timing components, 12-month warranty | If timing failure has caused valve damage | 1 - 2 days |
Vehicle Value Check
Vehicle Value Check
A typical 2011-2013 S 350 is worth approximately £8,000-£18,000 depending on mileage and condition. The S-Class retains strong residual values - replacement cost is typically justified for well-maintained examples.
Our Recommendation
Our Recommendation
If your S 350 exhibits a rattling noise on cold start, act immediately. The M276's timing chain tensioners are a known weak point. Specialist tensioner replacement at £700-£1,200 is significantly cheaper than dealer rates. If the chain has stretched or jumped timing, a full rebuilt M276 engine is the only safe option.
Don't Let Timing Chain Rattle, Wiring Harness Degradation, or 48V Issues Write Off Your Mercedes S 350 or 450 Petrol
Whether you're facing M276 timing chain rattle on your S 350 or M256 wiring harness degradation on your S 450, EnginesMarket makes it simple to compare quotes from trusted UK Mercedes petrol specialists. Every rebuilt engine in our network carries upgraded components addressing the original design weakness - improved tensioners, heat-resistant wiring harnesses, and new seals - plus a minimum 12-month unlimited mileage warranty with nationwide delivery and supply & fit options. Don't pay main dealer premiums. Compare prices from independent Mercedes specialists who know these flagship petrol engines inside out.
Compare rebuilt M276 Mercedes S 350 engine prices
12-Month Minimum
UK Specialists Vetted
Best Price GuidanceImportant Information
Important Information
"All prices are indicative UK market ranges based on historical quote data and repair requests from our network of engine specialists. Dealer pricing is estimated based on published main dealer labour rates and genuine OEM parts pricing. Specialist pricing reflects actual quote data from EnginesMarket's UK network. Actual costs vary depending on damage severity, vehicle condition, variant, and workshop location within the UK. Use our free comparison tool to get tailored quotes for your specific Mercedes S Class 350 or 450 petrol. Every engine supplied through EnginesMarket carries a minimum 12-month unlimited mileage warranty - always confirm exact terms with your chosen supplier."
Mercedes Benz S Class 350/450 Petrol Engine ReplacementFrequently Asked Questions
Question 1How much does a Mercedes S 350 or S 450 petrol engine replacement cost in the UK-
Short summary: A rebuilt M276 engine for the S 350 costs £3,200-£4,500 supply-only; a rebuilt M256 engine for the S 450 costs £4,200-£5,400 supply-only. Fitting adds £1,200-£2,500 depending on complexity - both engines require specialist knowledge.
- S 350 (M276.950): rebuilt unit £3,200-£4,500; used engine from £1,500
- S 450 (M256.930): rebuilt unit £4,200-£5,400; used engine from £2,200
- M276 timing chain tensioner replacement: £700-£1,200 at specialist
- M256 wiring harness replacement: £800-£1,400 at specialist
Question 2What are the signs of timing chain failure on a Mercedes S 350-
Short summary: A rattling noise on cold start lasting a few seconds is the classic warning sign on the M276 V6 engine. The hydraulic secondary chain tensioners can lose oil pressure, allowing chain slack.
- Cold start rattle that disappears after oil pressure builds - earliest warning
- Check engine light with timing correlation codes
- Mercedes TSB LI05.10-P-056435 covers updated tensioners and check valves
- If caught early, tensioner replacement costs £700-£1,200 at specialist
Question 3Is the Mercedes S 450 engine (M256) reliable-
Short summary: The M256 inline-six is a modern, sophisticated engine, but it has known wiring harness degradation issues and 48V system vulnerabilities. With these addressed, the engine is proving durable.
- Wiring harness degradation near turbocharger is the most common electrical issue
- 48V battery and ISG failures can cause warning lights and loss of EQ Boost
- Oil consumption between services has been reported
- Well-maintained M256 engines exceed 100,000 miles
Question 4How long do Mercedes S 350 and S 450 petrol engines last-
Short summary: Properly maintained M276 V6 engines routinely reach 150,000-200,000 miles before major work. The M256 is too new for definitive long-term data, but with proactive maintenance, 100,000+ miles is achievable.
- M276 (S 350): 150,000-200,000 miles with regular servicing
- M256 (S 450): too early for definitive data - wiring and 48V issues from 30k-60k miles
- Service interval is 10,000 miles or 12 months - use Mercedes-spec MB 229.5 oil
- Late oil changes accelerate timing chain wear on M276 and wiring degradation on M256
Question 5Is it worth replacing the engine in my Mercedes S 350 or S 450 petrol-
Short summary: Yes, if the S-Class is otherwise in good condition with no rust or major electrical faults. A rebuilt M276 costs £3,200-£4,500 - far less than replacing an £8,000-£18,000 vehicle. The S 450's higher value (£35,000-£60,000) makes replacement even more financially justifiable.
- S 350 values: £8,000-£18,000 depending on year, mileage and condition
- S 450 values: £35,000-£60,000 - flagship residual values remain strong
- Rebuilt engine with upgraded components fixes original weak points
- Supply & fit typically £4,400-£7,900 depending on engine code
- New engine includes 12-month unlimited mileage warranty
Question 6What oil does my Mercedes S 350 or S 450 petrol need-
Short summary: Mercedes-Benz specifies MB 229.5 high-performance oil - typically 5W-30 or 5W-40 fully synthetic. The M276 V6 requires approximately 7.5 litres; the M256 inline-six requires approximately 8.0 litres.
- M276 (S 350): MB 229.5 5W-30 or 5W-40 - 7.5L capacity
- M256 (S 450): MB 229.5 5W-30 or 5W-40 - 8.0L capacity
- Never use non-approved oil - can cause timing chain and hydraulic lifter issues
- Change every 10,000 miles or 12 months - stretched intervals cause timing chain wear
Why Choose UsCompare Mercedes S Class 350/450 PetrolEngine PricesToday
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supply & fit available for M276 and M256
Comparing quotes for your Mercedes S 350 or S 450 petrol is completely free, with no obligation and no pressure. Enter your registration above to get tailored quotes from UK Mercedes petrol specialists who understand the M276 V6 and M256 inline-six engines inside out. Whether you need a used engine, a reconditioned unit, or a full rebuilt engine with upgraded timing components, heat-resistant wiring harnesses, and new seals, we'll connect you with the right specialist for your exact S-Class - with a minimum 12-month warranty on every engine supplied.
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