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Mercedes-Benz OM629 Engine - Replacement Cost, Problems & CompatibilityProblems & Compatibility
The OM629 is Mercedes-Benz’s refined 4.0-litre V8 bi-turbo common-rail diesel, succeeding the OM628 in flagship models like the W211 E-Class, W221 S-Class, and X164 GL-Class. Reconditioned OM629 engines typically start from £3,500 , offering immense torque with improved piezo-injector technology, though it remains a complex unit requiring specialist care.
Supply & Fit Available
12-Month Warranty
Nationwide Delivery
100+ Suppliers
Used from
£1,500
Reconditioned from
£3,500
Rebuilt from
£5,500
GB
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Key Specs
Mercedes-Benz OM629 - Specifications at a Glance
Engine Code
OM629.990
Fuel
Diesel
Configuration
4.0L V8, DOHC, 32-valve, bi-turbo common-rail (CDI)
Power Output(s)
225 kW (306 hp) - 231 kW (314 hp)
Years Produced
2005-2010
UK Models Fitted
4 Mercedes model families - full list in Compatibility below
Replaced
OM628
Replaced By
OM642 (in the flagship diesel role)
Most Common Failure
Turbocharger oil feed coking and injector seal weeping
Reconditioned Price Range
£3,500-£5,500 supply-only
Vetted UK specialists for OM629 replacements
Minimum 12-month warranty on reconditioned and rebuilt options
Fitted To
Which Mercedes Models Use the OM629-
The OM629 was Mercedes-Benz’s premium V8 diesel for the mid-to-late 2000s, designed to provide massive low-end torque and effortless cruising ability for their heaviest and most luxurious chassis, bridging the gap between the older OM628 and the later V6-centric OM642 era.
| Model | Generation/Chassis | Badge(s) | Years | Link |
|---|---|---|---|---|
 Mercedes-Benz E-Class | W211 | E 420 CDI | 2006-2009 | |
| Mercedes-Benz S-Class | W221 | S 420 CDI | 2006-2009 | |
| Mercedes-Benz M-Class | W164 | ML 420 CDI | 2006-2009 | |
| Mercedes-Benz GL-Class | X164 | GL 420 CDI | 2006-2009 |
02
Mercedes-Benz S-Class
03
Mercedes-Benz M-Class
04
Mercedes-Benz GL-Class
CROSS-BRAND
OM629 is documented across 4 BMW applications spanning E-Class, S-Class, M-Class, GL-Class. Registration lookup confirms the exact suffix before quotes are sent.
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Prices
Mercedes-Benz OM629 Engine Replacement Cost (UK)
Condition | Supply Only | Fitted (Independent Specialist) | Typical Warranty |
|---|---|---|---|
Used | £1,500-£2,500 | £2,800-£4,500 | 3-6 months |
Reconditioned | £3,500-£5,500 | £5,000-£7,800 | 12-24 months |
Rebuilt | £5,500-£8,000 | £7,500-£10,500 | 12-24 months |
What genuinely moves the price for this engine is the condition of the piezo-electric injectors and the twin turbocharger oil feed lines. Because the OM629 is a highly complex V8, recon specialists will typically strip the entire top end to clean carbon buildup, replace all turbo oil lines as standard, and verify the piezo injector spray patterns. For a full breakdown of market rates, see our full reconditioned engine cost guide.
Labour Guide
Fitting an OM629 engine typically takes 15-20 hours at £75-£95/hr (independent specialist) - the engine bay is incredibly tight, often requiring a subframe drop or engine-out approach via the top.
Price Factors
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Common Problems
Mercedes-Benz OM629 Engine Problems - What Actually Fails
Every engine has its weak points. Here are the known issues with the OM629, based on real-world data and verified failure patterns.
Verified issue focus: Turbocharger oil feed coking and injector seal weeping.
1. Turbocharger Oil Feed Coking - Bi-turbo setup
1. Turbocharger Oil Feed Coking - Bi-turbo setup
Typical onset:
80,000-120,000 miles
What happens:
The twin turbochargers rely on specific oil feed lines that are prone to heat-soak and coking, especially if oil change intervals were extended or incorrect oil specs were used. Restricted oil flow starves the turbo bearings, leading to shaft play, severe whining, blue smoke, and eventual catastrophic turbo failure.
Repair vs replace:
If caught before the turbos destroy themselves, the oil feed lines and banjo bolts can be replaced. If the turbos have failed and sent metal through the engine, a full replacement unit is required.
Read more about this issue
2. Injector Seal Weeping ("Black Death") - All variants
2. Injector Seal Weeping ("Black Death") - All variants
Typical onset:
90,000+ miles
What happens:
The copper washer seals at the base of the piezo-electric injectors degrade over time, allowing high-pressure combustion gases to escape. This creates a black, crusty carbon buildup around the injector heads, leading to a distinct tapping noise, rough idling, and a strong smell of exhaust in the cabin.
Repair vs replace:
This is a routine maintenance item, not a terminal failure. Replacing the seals and cleaning the cylinder head is inexpensive and should be done preventatively.
Read more about this issue
3. EGR and Swirl Flap Carbon Buildup - All variants
3. EGR and Swirl Flap Carbon Buildup - All variants
Typical onset:
100,000+ miles
What happens:
The complex intake manifold houses swirl flaps that become clogged with EGR soot over time, restricting airflow and triggering limp mode. This is exacerbated by the V8 layout, which traps heat and accelerates carbon deposition.
Repair vs replace:
Intake manifolds often require replacement or professional ultrasonic cleaning. A verified swirl flap delete is a common and effective preventative measure performed during a rebuild.
Read more about this issue
The OM629 resolved several of the OM628's early teething issues with revised piezo injectors and better engine management, making it a more robust unit overall. However, units with meticulously documented turbo oil line maintenance are highly prized, as neglected examples can easily generate repair bills that exceed the host vehicle's entire market value .
Compare rebuilt OM629 engine prices with the failure already addressed
Engine Variants
How to Confirm You Have the Mercedes-Benz OM629
The engine code is stamped on the left-hand side of the cylinder block, near the bellhousing. It will also be listed on your V5C logbook under "Engine Capacity" or visible via a VIN decode. The OM629 is frequently confused with its predecessor, the OM628 (which used solenoid injectors and had earlier teething issues), or the later 3.0L V6 OM642 which eventually took over the flagship diesel role. Fitting the wrong revision or assuming interchangeability matters significantly: the OM629 requires specific ECU mapping for its piezo-electric injectors, distinct turbo plumbing, and different engine mount configurations that will not function correctly if swapped with an OM628 or an OM642.
Not sure which engine your car has- Enter your registration above - we'll confirm your exact OM629 fitment before any quotes are sent.
Easily Confused
OM628
the 4.0L V8 bi-turbo diesel that the OM629 evolved from, introducing piezo-electric injectors and refined emissions hardware to address the OM628's early teething issues.
Alternative / Next-Gen Code
OM642
the 3.0L V6 CDI that eventually took over the flagship diesel role across the E-Class, S-Class, and GL-Class range, delivering comparable torque with improved fuel efficiency and a less complex V-layout.
Related JLR Variants
OM613
the 3.2L inline-5 CDI that shared the same early-2000s common-rail architecture and electronic injection principles, but in a longitudinally mounted 5-cylinder configuration for slightly lighter chassis applications.
Confirm the exact OM629 fitment
Not sure which engine your car has- Enter your registration above - we'll confirm your exact OM629 fitment before any quotes are sent.
Buying Guide
Buying a Replacement OM629 Engine - What to Choose
Choosing the right replacement route depends on your budget, risk tolerance, and ownership goals. Here's a breakdown of your options.
Used:
A used OM629 engine is an extreme financial risk unless it comes with verifiable, recent documentation of a turbo oil feed line upgrade and injector seal replacement. Given the engine-out labour required to fix these items, buying a used unit with unknown history often leads to an immediate £3,000+ teardown bill.
Reconditioned:
A proper reconditioned OM629 engine is the only sensible choice for most buyers. A reputable rebuild will proactively address the fatal flaws by installing upgraded turbo oil feed lines, verifying piezo injector spray patterns, and replacing all injector seals, while ultrasonically cleaning the complex intake manifold.
Rebuilt:
A full OM629 engine rebuild is justified for pristine X164 GL-Class or W221 S-Class restorations where maximum longevity and originality are required. An upgraded rebuild should include line-boring, balanced internals, and upgraded turbo coolant and oil lines.
Supply & Fit Line:
Sourcing and fitting through our vetted network ensures your OM629 engine is installed by specialists equipped for heavy V8 diesel extraction, backed by a nationwide warranty.
Vehicle Value Note:
Because the OM629 is typically found in W211, W221, W164, and X164 vehicles valued between £5,000 and £18,000 for standard examples, a full replacement can represent a significant portion of the host's worth. If the lowest viable replacement cost exceeds approximately 60% of the vehicle's current market value, evaluate scrap value before committing .
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Related Engines
Engines Related to the Mercedes-Benz OM629
Explore engines that are closely related to the Mercedes-Benz OM629, including its predecessor, successor, and key family variants.
Predecessor
OM628
the 4.0L V8 bi-turbo diesel that the OM629 evolved from, introducing piezo-electric injectors and refined emissions hardware to address the OM628's early teething issues.
Successor
OM642
the 3.0L V6 CDI that eventually took over the flagship diesel role across the E-Class, S-Class, and GL-Class range, delivering comparable torque with improved fuel efficiency and a less complex V-layout.
Sibling
OM613
the 3.2L inline-5 CDI that shared the same early-2000s common-rail architecture and electronic injection principles, but in a longitudinally mounted 5-cylinder configuration for slightly lighter chassis applications.
FAQ
Mercedes-Benz OM629Frequently Asked Questions
Question 1How much does a Mercedes OM629 engine replacement cost-
A reconditioned Mercedes OM629 engine typically costs between £3,500 and £5,500 for supply only . Fitted costs generally range from £5,000 to £7,800 depending on the specialist, while used units can be found from £1,500 but carry a high financial risk due to the engine's complex failure profile. Compare OM629 engine replacement quotes today
Compare OM629 quotesQuestion 2What is the most common failure on the OM629 engine-
The most documented issues are turbocharger oil feed line coking, injector seal weeping ("Black Death"), and EGR/swirl flap carbon buildup. Coked oil lines can starve the twin turbos and cause catastrophic bearing failure, while injector seal failure is a cheaper but mandatory preventative maintenance item. Get quotes for a rebuilt OM629 with these issues resolved
Compare OM629 quotesQuestion 3Which Mercedes models use the OM629 engine-
The OM629 was fitted to the W211 E-Class (E 420 CDI), the W221 S-Class (S 420 CDI), the W164 M-Class (ML 420 CDI), and the X164 GL-Class (GL 420 CDI), serving as Mercedes' premium V8 diesel for their heaviest chassis between 2005 and 2010. Check your registration to confirm your exact OM629 fitment
Compare OM629 quotesQuestion 4Should I buy a used or reconditioned OM629 engine-
A reconditioned OM629 is strongly recommended over a used unit. A proper rebuild will proactively address the fatal flaws by installing upgraded turbo oil feed lines, verifying piezo injector spray patterns, and replacing all injector seals, whereas a used engine with unknown history often leads to an immediate £3,000+ teardown bill if the turbos fail shortly after installation. Compare reconditioned OM629 engine prices from UK specialists
Compare OM629 quotesQuestion 5How do I know if my car has the OM629 and not the OM628 or OM642-
The OM629 is a 4.0L V8 diesel with piezo-electric injectors, distinct from the solenoid-injected OM628 or the 3.0L V6 OM642. The engine code is stamped on the left-hand side of the cylinder block near the bellhousing and is also listed on your V5C logbook. Enter your reg above to identify your exact engine code ═══════════════════════════════════════
Compare OM629 quotesCompare Mercedes-Benz OM629 Engine Prices Today
Vetted UK specialists who work on complex Mercedes V8 diesel systems like the OM629 every week Minimum 12-month warranty on every reconditioned and rebuilt OM629 engine Nationwide delivery - supply-only or full supply & fit available across the UK Get a free, no-obligation comparison of OM629 engine prices tailored to your exact vehicle. Our registration lookup confirms your fitment before any quotes are sent, ensuring you receive the correct unit with matching ancillary components. With reconditioned OM629 engines starting from an estimated £3,500, comparing takes two minutes and could save you thousands on labour and unexpected teardowns.
Vetted UK Specialists
Vetted UK specialists for OM629 replacements
Minimum 12-Month Warranty
Minimum 12-month warranty on reconditioned and rebuilt options
Nationwide Delivery
Nationwide delivery plus supply and fit availability
Expert Support
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