Mercedes Benz S Class 320 CDI/350 CDI Engine ReplacementCompare Prices & Get Quotes
Get quotes today from trusted UK Mercedes Benz S Class 320 CDI and 350 CDI engine specialists. Compare prices on reconditioned, rebuilt and used engines for the 3.0-litre OM642 V6 diesel - supply & fit available nationwide.
Supply & Fit Available
12-Month Warranty
Nationwide Delivery
100+ Suppliers
From £1,800 to £4,300
Used from £1,200 · Reconditioned from £1,800 · Common codes: OM642.930, OM642.931, OM642.932, OM642.861, OM642.862
From £1,200
Tested, bare/short engine
From £1,800
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 320 CDI/350 CDI Replacement Engineto Finding the Best Mercedes Benz S Class 320 CDI/350 CDI Replacement Engine
Most replacements completed within 3-5 days.
Variant HistoryMercedes Benz S Class 320 CDI/350 CDI - Engine History & Specs at a Glance
The S 320 CDI launched with the W221 generation in 2005 as Mercedes' flagship diesel, powered by the OM642 3.0-litre V6 diesel producing 235hp. The S 350 CDI joined the range using the same OM642 V6 architecture, with outputs ranging from 235hp to 258hp in later BlueTEC form. In 2009, the facelift W221 introduced BlueTEC technology with AdBlue SCR systems, improving emissions compliance. Both variants continued through to 2013 when the W222 generation replaced them.
Variant HistoryMercedes Benz S Class 320 CDI/350 CDI - Engine History & Specs at a Glance
The S 320 CDI launched with the W221 generation in 2005 as Mercedes' flagship diesel, powered by the OM642 3.0-litre V6 diesel producing 235hp. The S 350 CDI joined the range using the same OM642 V6 architecture, with outputs ranging from 235hp to 258hp in later BlueTEC form. In 2009, the facelift W221 introduced BlueTEC technology with AdBlue SCR systems, improving emissions compliance. Both variants continued through to 2013 when the W222 generation replaced them.
Mercedes Benz S Class 320 CDI/350 CDI
Fuel TypeDiesel (V6 turbodiesel with common-rail injection; BlueTEC with AdBlue SCR)
Engine Size3.0L (2,987cc)
Power Output Range211-258hp across the variant's historyEngine History Timeline
OM642.930 3.0L V6 diesel, 235hp @ 3,600rpm (S 320 CDI, W221 launch)
OM642.931/932 3.0L V6 diesel, 211-235hp (4MATIC variants)
OM642.862 3.0L V6 BlueTEC diesel, 258hp (S 350 CDI BlueTEC, facelift W221)
End of W221 production; replaced by S 350 BlueTEC in W222 generation
Key Specs Snapshot
Fuel TypeDiesel (V6 turbodiesel with common-rail injection; BlueTEC with AdBlue SCR)Engine Size3.0L (2,987cc)Power Output Range211-258hp across the variant's historyYears Produced2005-2013Every engine fitted to the Mercedes Benz S Class 320 CDI and 350 CDI is covered below, with UK rebuilt pricing and known failure points - from OM642 timing chain stretch to oil cooler seal degradation and BlueTEC AdBlue system issues.
Mercedes Benz S Class 320 CDI/350 CDI Engine Codes - Specifications & Replacement CostMercedes Benz S Class 320 CDI/350 CDI Engine Codes - Specifications & Replacement Cost
3.0L V6 Diesel (2005-2013)
Power Output235 hp (173 kW) @ 3,600 rpmTorque540 Nm @ 1,600-2,800 rpmYears Fitted2005-2013Displacement2,987 ccCylindersV6, 72° V-angle, 24-valve, DOHCEngine CodeOM 642 DE 30 LA / 642.930
Compatible Trim Levels
- S 320 CDI
- S 320 CDI 4MATIC
- S 350 CDI
- S 350 CDI 4MATIC
Find your exact engine code, specs and UK replacement cost guide.
Used
Tested, ready-to-fit engine
£1,200-£2,000
Reconditioned
Addressed known issues, tested
£1,800-£2,800
Rebuilt
Full teardown, upgraded internals
£2,200-£3,500
Common Failure
Timing chain stretch and guide failure - the OM642 V6 is a refined and durable engine, but timing chain tensioner wear can cause cold-start rattling and, if ignored, catastrophic engine failure. Oil cooler seal degradation is also common, with leaks in the V of the engine.
The S 320 CDI and S 350 CDI's OM642 V6 diesel is a refined and durable engine, but it has well-documented weaknesses that become more pronounced with age and mileage. Timing chain stretch, oil cooler seal degradation, and BlueTEC AdBlue system issues are the most common failure patterns driving replacement decisions. Every rebuilt engine supplied through EnginesMarket includes upgraded components addressing these original failure points, plus a minimum 12-month unlimited-mileage warranty.
The S 320/350 CDI's Most Critical Weakness
Affected Vehicles
Mercedes S 320 CDI, S 350 CDI, S 350 CDI BlueTEC (OM642.930, OM642.931, OM642.932, OM642.861, OM642.862, 2005-2013)
Typical Failure Mileage
80,000-120,000 miles
Root Cause
The timing chain tensioner can lose hydraulic pressure, allowing the chain to stretch and plastic guides to wear. This is a known issue on the OM642 V6. One owner reported an OM642 engine seizing at 120,000 miles. Intermittent starting problems have also been traced to stretched timing chains causing cam and crank sensor misalignment.
Why It Happens
The timing chain tensioner can lose hydraulic pressure, allowing the chain to stretch and plastic guides to wear. This is a known issue on the OM642 V6. One owner reported an OM642 engine seizing at 120,000 miles. Intermittent starting problems have also been traced to stretched timing chains causing cam and crank sensor misalignment.
Dealer (parts + labour)
£300-£500
Specialist (parts + labour)
£150-£300
What it involves
STAR diagnostic, cam/crank correlation check, borescope inspection
Suitability
First step - confirms whether chain is stretched
1 - 2 daysDealer (parts + labour)
£2,500-£4,000
Specialist (parts + labour)
£1,800-£2,800
What it involves
Replace timing chain, tensioner, guides, sprockets
Suitability
60k-80k miles if caught before chain stretches significantly
1 - 2 daysDealer (parts + labour)
£4,800-£6,500
Specialist (parts + labour)
£2,800-£4,600
What it involves
Complete engine swap with upgraded timing components, 12-month warranty
Suitability
If chain has jumped causing 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 |
|---|---|---|---|---|---|
 Diagnostics - Timing chain inspection Minor | £300-£500 | £150-£300 | STAR diagnostic, cam/crank correlation check, borescope inspection | First step - confirms whether chain is stretched | 1 - 2 days |
 Intermediate - Timing chain replacement Best Value | £2,500-£4,000 | £1,800-£2,800 | Replace timing chain, tensioner, guides, sprockets | 60k-80k miles if caught before chain stretches significantly | 1 - 2 days |
Full Replacement - Rebuilt OM642 engine Best Value | £4,800-£6,500 | £2,800-£4,600 | Complete engine swap with upgraded timing components, 12-month warranty | If chain has jumped causing valve damage | 1 - 2 days |
Vehicle Value Check
Vehicle Value Check
A typical 2005-2013 S 320 CDI or S 350 CDI is worth approximately £4,000-£15,000 depending on mileage and condition. These flagship saloons have suffered significant depreciation, meaning replacement costs can approach or exceed vehicle value for higher-mileage examples.
Our Recommendation
Our Recommendation
If you hear a rattling noise on cold start or experience intermittent starting problems on your S 320 CDI or S 350 CDI, act immediately. A stretched timing chain on the OM642 can cause catastrophic engine failure. Specialist timing chain replacement at £1,800-£2,800 is significantly cheaper than dealer rates. If the chain has already jumped, a full rebuilt OM642 engine is the only safe option.
Don't Let Timing Chain Stretch, Oil Cooler Seals, or AdBlue Issues Write Off Your Mercedes S 320 CDI or 350 CDI
Whether you're facing OM642 timing chain stretch on your S 320 CDI, oil cooler seal degradation, or BlueTEC AdBlue system issues on your S 350 CDI, EnginesMarket makes it simple to compare quotes from trusted UK Mercedes diesel specialists. Every rebuilt engine in our network carries upgraded components addressing the original design weakness - reinforced timing components, Viton oil cooler seals, and new AdBlue system parts - 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 OM642 V6 diesels inside out.
Compare rebuilt OM642 Mercedes S 320 CDI/350 CDI 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 320 CDI or 350 CDI. 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 320 CDI/350 CDI Engine ReplacementFrequently Asked Questions
Question 1How much does a Mercedes S 320 CDI or S 350 CDI engine replacement cost in the UK-
Short summary: A rebuilt OM642 engine for the S 320 CDI costs £2,200-£3,500 supply-only; a rebuilt OM642 BlueTEC engine for the S 350 CDI costs £2,500-£4,300 supply-only. Fitting adds £1,200-£2,500 depending on complexity.
- S 320 CDI (OM642.930/931/932): rebuilt unit £2,200-£3,500; used engine from £1,200
- S 350 CDI (OM642.930): rebuilt unit £2,300-£3,800; used engine from £1,300
- S 350 CDI BlueTEC (OM642.861/862): rebuilt unit £2,500-£4,300; used engine from £1,400
- OM642 timing chain replacement (labour only): £1,800-£2,800 at specialist
- OM642 oil cooler seal replacement: £950-£1,400 at specialist
Question 2What are the signs of timing chain failure on a Mercedes S 320 CDI or S 350 CDI-
Short summary: A rattling noise on cold start or intermittent starting problems are the classic warning signs on the OM642 engine. One owner reported an OM642 engine seizing at 120,000 miles.
- Cold start rattle that disappears after oil pressure builds - earliest warning
- Intermittent starting - engine cranks but fails to start; timing chain stretch causes cam and crank sensors to misalign
- Check engine light with timing correlation codes
- If caught early, chain replacement costs £1,800-£2,800 at specialist
Question 3Is the Mercedes S 320 CDI or S 350 CDI engine (OM642) reliable-
Short summary: The OM642 V6 is fundamentally robust, but S Class owners should be aware of timing chain stretch and oil cooler seal degradation. With these addressed, the engine is capable of 150,000+ miles.
- OM642 V6 is fundamentally robust with proven durability
- Timing chain stretch is the most critical failure point
- Oil cooler seal degradation affects many units from 80,000 miles
- Well-maintained OM642 engines exceed 150,000 miles
Question 4How long do Mercedes S 320 CDI and S 350 CDI engines last-
Short summary: Properly maintained OM642 engines routinely reach 150,000-200,000 miles before major work is needed.
- OM642 (S 320/350 CDI): 150,000-200,000+ miles with regular servicing
- Timing chain inspection recommended from 80,000 miles
- Service interval is 10,000 miles or 12 months - use Mercedes-spec low-SAPS oil (MB 229.51/229.52)
- Late oil changes accelerate timing chain wear and oil cooler seal degradation
Question 5Is it worth replacing the engine in my Mercedes S 320 CDI or S 350 CDI-
Short summary: Yes, if the S Class is otherwise in good condition with no rust or major transmission faults. A rebuilt OM642 costs £2,200-£3,500 - comparable to the value of a £4,000-£15,000 vehicle, making it a justifiable investment for well-maintained examples.
- S 320 CDI values: £4,000-£12,000 depending on year, mileage and condition
- S 350 CDI values: £4,000-£15,000 - flagship saloon values remain strong for well-maintained examples
- Rebuilt engine with upgraded components fixes original weak points
- Supply & fit typically £3,400-£6,000 depending on engine code
- New engine includes 12-month unlimited mileage warranty
Question 6What oil does my Mercedes S 320 CDI or S 350 CDI need-
Short summary: Mercedes-Benz specifies low-SAPS oil meeting MB 229.51 or 229.52 - typically 5W-30. The OM642 V6 requires approximately 8.5-9.5 litres with filter.
- OM642 (S 320/350 CDI): MB 229.51/229.52 5W-30 low-SAPS
- Never use non-approved oil - can cause timing chain and injector issues
- Change every 10,000 miles or 12 months - stretched intervals cause timing chain wear
Why Choose UsCompare Mercedes S Class 320 CDI/350 CDIEngine PricesToday
500+ OM642 V6 diesel engines supplied through our network
12-Month Warranty on every rebuilt S 320 CDI and S 350 CDI engine
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supply & fit available for OM642
Comparing quotes for your Mercedes S 320 CDI or S 350 CDI is completely free, with no obligation and no pressure. Enter your registration above to get tailored quotes from UK Mercedes diesel specialists who understand the OM642 V6 engine inside out. Whether you need a used engine, a reconditioned unit, or a full rebuilt engine with upgraded timing components, oil cooler seals, and AdBlue system parts, 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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