Mercedes Benz S Class 300/320 CDI Engine ReplacementCompare Prices & Get Quotes
Get quotes today from trusted UK Mercedes Benz S Class 300 CDI and 320 CDI engine specialists. Compare prices on reconditioned, rebuilt and used engines for the 3.0-litre OM642 V6 diesel and the 2.1-litre OM651 four-cylinder - supply & fit available nationwide.
Supply & Fit Available
12-Month Warranty
Nationwide Delivery
100+ Suppliers
From £1,800 to £3,500
Used from £1,200 · Reconditioned from £1,800 · Common codes: OM642.930, OM642.931, OM642.932, OM651
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 300/320 CDI Replacement Engineto Finding the Best Mercedes Benz S Class 300/320 CDI Replacement Engine
Most replacements completed within 3-5 days.
Variant HistoryMercedes Benz S Class 300/320 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 300 CDI joined the range as an entry-level diesel option, using the same OM642 V6 architecture in a lower-output configuration. In 2009, the S 300 BlueTEC Hybrid introduced the OM651 2.1-litre four-cylinder diesel paired with an electric motor, marking Mercedes' first step into hybrid luxury. The S 320 CDI continued through the W221 lifecycle until 2013, when it was replaced by the S 350 BlueTEC in the W222 generation.
Variant HistoryMercedes Benz S Class 300/320 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 300 CDI joined the range as an entry-level diesel option, using the same OM642 V6 architecture in a lower-output configuration. In 2009, the S 300 BlueTEC Hybrid introduced the OM651 2.1-litre four-cylinder diesel paired with an electric motor, marking Mercedes' first step into hybrid luxury. The S 320 CDI continued through the W221 lifecycle until 2013, when it was replaced by the S 350 BlueTEC in the W222 generation.
Mercedes Benz S Class 300/320 CDI
Fuel TypeDiesel (V6 turbodiesel; four-cylinder hybrid diesel)
Engine Size Range2.1L-3.0L (OM642: 2,987cc; OM651: 2,143cc)
Power Output Range204-235hp across the variant's historyEngine History Timeline
OM642.930 3.0L V6 diesel, 235hp (S 320 CDI, W221 launch)
OM642.931/932 3.0L V6 diesel, 235hp (S 320 CDI 4MATIC variants)
OM651 2.1L four-cylinder diesel hybrid (S 300 BlueTEC Hybrid)
End of W221 production; S 320 CDI replaced by S 350 BlueTEC in W222
Key Specs Snapshot
Fuel TypeDiesel (V6 turbodiesel; four-cylinder hybrid diesel)Engine Size Range2.1L-3.0L (OM642: 2,987cc; OM651: 2,143cc)Power Output Range204-235hp across the variant's historyYears Produced2005-2013Every engine fitted to the Mercedes Benz S Class 300 CDI and 320 CDI is covered below, with UK rebuilt pricing and known failure points - from OM642 timing chain stretch to OM651 injector seal leaks.
Mercedes Benz S Class 300/320 CDI Engine Codes - Specifications & Replacement CostMercedes Benz S Class 300/320 CDI Engine Codes - Specifications & Replacement Cost
3.0L V6 Diesel (2005-2009)
Power Output235 hp (173 kW) @ 3,800 rpmTorque540 Nm @ 1,600-2,400 rpmYears Fitted2005-2009Displacement2,987 ccCylindersV6, 24-valve, aluminium blockEngine CodeOM 642 DE 30 LA / 642.930
Compatible Trim Levels
- S 320 CDI
- S 320 CDI 4MATIC
- S 320 CDI Long
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 between the V of the engine. One owner reported a timing chain failure at only 56,000 miles, requiring a full engine rebuild.
The S 320 CDI's OM642 V6 and the S 300 CDI's OM651 four-cylinder are fundamentally robust diesel engines, but both have well-documented weaknesses that become more pronounced with age and mileage. The OM642 is prone to timing chain stretch and oil cooler seal degradation, while the OM651 suffers from injector seal leaks. 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 CDI's Most Critical Weakness
Affected Vehicles
Mercedes S 320 CDI, S 320 CDI 4MATIC (OM642.930, OM642.931, OM642.932, 2005-2009)
Typical Failure Mileage
80,000-120,000 miles (can occur as early as 56,000 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 a timing chain failure at only 56,000 miles, requiring a full engine rebuild. 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 a timing chain failure at only 56,000 miles, requiring a full engine rebuild. 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 is worth approximately £4,000-£12,000 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, 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 Injector Leaks Write Off Your Mercedes S 300 CDI or 320 CDI
Whether you're facing OM642 timing chain stretch on your S 320 CDI, oil cooler seal degradation, or OM651 injector seal leaks on your S 300 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 injector 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 diesel engines inside out.
Compare rebuilt OM642 Mercedes S 320 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 300 CDI or 320 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 300/320 CDI Engine ReplacementFrequently Asked Questions
Question 1How much does a Mercedes S 320 CDI or S 300 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 OM651 engine for the S 300 CDI costs £2,000-£3,000 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 300 CDI (OM651): rebuilt unit £2,000-£3,000; used engine from £1,000
- 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-
Short summary: A rattling noise on cold start or intermittent starting problems are the classic warning signs on the OM642 engine. One owner reported a timing chain failure at only 56,000 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 engine (OM642) reliable-
Short summary: The OM642 V6 is fundamentally robust, but S 320 CDI 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 - can occur as early as 56,000 miles
- 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 300 CDI engines last-
Short summary: Properly maintained OM642 engines routinely reach 150,000-200,000 miles before major work is needed. The OM651 is also durable but requires attention to injector seals.
- OM642 (S 320 CDI): 150,000-200,000+ miles with regular servicing
- OM651 (S 300 CDI): 150,000+ miles with regular servicing
- Timing chain inspection recommended from 80,000 miles on OM642
- Service interval is 10,000 miles or 12 months - use Mercedes-spec low-SAPS oil (MB 229.51)
Question 5Is it worth replacing the engine in my Mercedes S 320 CDI or S 300 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-£12,000 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 300 CDI values: £3,000-£8,000
- 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 300 CDI need-
Short summary: Mercedes-Benz specifies low-SAPS oil meeting MB 229.51 - typically 5W-30. The OM642 V6 requires approximately 8.5 litres with filter; the OM651 requires approximately 6.5 litres.
- OM642 (S 320 CDI): MB 229.51 5W-30 low-SAPS
- OM651 (S 300 CDI): MB 229.51 5W-30 low-SAPS - 6.5L capacity
- 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 300/320 CDIEngine PricesToday
500+ OM642 and OM651 diesel engines supplied through our network
12-Month Warranty on every rebuilt S 320 CDI and S 300 CDI engine
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supply & fit available for OM642 and OM651
Comparing quotes for your Mercedes S 320 CDI or S 300 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 and OM651 four-cylinder engines inside out. Whether you need a used engine, a reconditioned unit, or a full rebuilt engine with upgraded timing components, oil cooler seals, and injector 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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