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Mercedes-Benz OM651.911/912 Engine - Replacement Cost, Problems & CompatibilityProblems & Compatibility
The OM651.911 and OM651.912 are Mercedes-Benz’s 2.1-litre inline-4 common-rail diesel (CDI) engines, primarily fitted to the W204 C-Class and W212 E-Class. Reconditioned OM651 engines typically start from £2,800 , and with 1,250 UK replacement requests in 2025 , it remains one of the most sought-after units for premium Mercedes restorations and high-mileage repairs.
Supply & Fit Available
12-Month Warranty
Nationwide Delivery
100+ Suppliers
Used from
£1,500
Reconditioned from
£2,800
Rebuilt from
£4,000
GB
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Key Specs
Mercedes-Benz OM651.911/912 - Specifications at a Glance
Engine Code
OM651.911 / OM651.912
Fuel
Diesel
Configuration
2.1L inline-4, DOHC, 16-valve, common-rail (CDI)
Power Output(s)
100 kW (136 hp) - 125 kW (170 hp)
Years Produced
2008-2014
UK Models Fitted
2 Mercedes model families - full list in Compatibility below
2025 UK Replacement Requests
1,250
Replaced
OM646
Replaced By
OM654
Most Common Failure
Timing chain tensioner wear and injector seal weeping
Reconditioned Price Range
£2,800-£4,800 supply-only
Vetted UK specialists for OM651.911/912 replacements
Minimum 12-month warranty on reconditioned and rebuilt options
Fitted To
Which Mercedes Models Use the OM651.911/912-
The OM651.911 and .912 were the definitive 4-cylinder CDI engines for Mercedes-Benz's core saloon range in the late 2000s and early 2010s, offering a highly efficient balance of torque and fuel economy before the introduction of the OM654.
02
Mercedes-Benz E-Class
CROSS-BRAND
OM651.911/912 is documented across 2 BMW applications spanning C-Class, E-Class. Registration lookup confirms the exact suffix before quotes are sent.
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Prices
Mercedes-Benz OM651.911/912 Engine Replacement Cost (UK)
Condition | Supply Only | Fitted (Independent Specialist) | Typical Warranty |
|---|---|---|---|
Used | £1,500-£2,800 | £2,020-£3,580 | 3-6 months |
Reconditioned | £2,800-£4,800 | £3,320-£5,580 | 12-24 months |
Rebuilt | £4,000-£6,000 | £4,520-£6,780 | 12-24 months |
What genuinely moves the price for this engine is whether the notorious timing chain tensioner (subject to TSB LI80.20-P-050001) and injector seals have been proactively replaced. Because the OM651 is a highly complex common-rail unit, recon specialists will typically strip the top end to replace all critical seals and verify the chain tensioner upgrade as standard. For a full breakdown of market rates, see our full reconditioned engine cost guide.
Labour Guide
Fitting an OM651 engine typically takes 8-12 hours at £65-£85/hr (independent) - confirm exact labour when comparing quotes.
Price Factors
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Common Problems
Mercedes-Benz OM651.911/912 Engine Problems - What Actually Fails
Every engine has its weak points. Here are the known issues with the OM651.911/912, based on real-world data and verified failure patterns.
Verified issue focus: Timing chain tensioner wear and injector seal weeping.
1. Timing Chain Tensioner Wear (TSB LI80.20-P-050001)
1. Timing Chain Tensioner Wear (TSB LI80.20-P-050001)
Typical onset:
80,000-150,000 miles
What happens:
The early OM651 timing chain tensioner can fail, leading to chain slack, a distinct metallic rattle on cold starts, and potentially catastrophic valve-to-piston contact if the chain jumps a tooth.
Repair vs replace:
Mercedes issued an updated tensioner design to resolve this. If caught early, replacing the tensioner and chain is cost-effective. If valve damage has already occurred, a full reconditioned OM651 unit is required.
Read more about this issue
2. Injector Seal Weeping ("Black Death")
2. Injector Seal Weeping ("Black Death")
Typical onset:
80,000-150,000 miles
What happens:
The copper washer seals at the base of the injectors degrade, 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. DPF and EGR Clogging
3. DPF and EGR Clogging
Typical onset:
100,000+ miles
What happens:
Urban driving patterns cause excessive soot buildup in the EGR valve and Diesel Particulate Filter (DPF), leading to restricted airflow, limp mode, and increased backpressure that can prematurely wear the turbocharger.
Repair vs replace:
Professional DPF cleaning or EGR replacement is a standard repair. If the turbocharger has suffered damage from prolonged backpressure, a full turbo rebuild or replacement is necessary.
Read more about this issue
Post-2011 units with the updated timing chain tensioner and revised ECU mapping show significantly fewer catastrophic chain failures, making them the most desirable examples of this engine family .
Compare rebuilt OM651.911/912 engine prices with the failure already addressed
Engine Variants
How to Confirm You Have the Mercedes-Benz OM651.911 or .912
The engine code is stamped on the right-hand side of the cylinder block, just above the oil filter housing. It will also be listed on your V5C logbook under "Engine Capacity" or visible via a VIN decode. The OM651.911 (typically 136 hp) and OM651.912 (typically 170 hp) are the core saloon variants of the OM651 family. They are sometimes confused with the van-oriented OM651.955-958 or the later OM651.924/925 variants. Fitting the wrong revision or assuming interchangeability matters significantly: the .911/.912 feature specific engine mounts, ECU mapping, and turbo plumbing that will not function correctly if swapped with a commercial van variant or a later-generation OM651 without significant modification.
Not sure which engine your car has- Enter your registration above - we'll confirm your exact OM651.911/912 fitment before any quotes are sent.
Easily Confused
OM646
the 2.1L inline-4 CDI that the OM651.911/912 refined, sharing the same common-rail architecture but with improved emissions compliance and a more robust timing chain design.
Alternative / Next-Gen Code
OM654
the modern 2.0L inline-4 CDI successor that eventually took over the C-Class and E-Class diesel roles, delivering improved fuel economy and reduced emissions.
Related JLR Variants
OM651.924/925
the 200 CDI variant of the same OM651 family, sharing the exact same block but with lower output tuning and different ECU mapping for specific chassis applications.
Confirm the exact OM651.911/912 fitment
Not sure which engine your car has- Enter your registration above - we'll confirm your exact OM651.911/912 fitment before any quotes are sent.
Buying Guide
Buying a Replacement OM651.911/912 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 OM651.911/912 engine makes sense only if it comes with verifiable service history and documented replacement of the timing chain tensioner and injector seals. Given the catastrophic risk of chain failure, buying a used unit with unknown history is a significant financial risk.
Reconditioned:
A proper reconditioned OM651 engine is the sweet spot for most buyers. A reputable rebuild will proactively address the common failure points by installing the updated timing chain tensioner, fitting new injector seals, and refreshing the EGR/DPF components, giving the engine a fresh lease on life.
Rebuilt:
A full OM651 engine rebuild is justified for high-mileage W212 E-Class or W204 C-Class hosts where originality and maximum longevity are required. An upgraded rebuild should include line-boring the block, new pistons/rings, and a balanced crankshaft.
Supply & Fit Line:
Sourcing and fitting through our vetted network ensures your OM651 engine is installed by specialists familiar with Mercedes CDI systems, backed by a nationwide warranty.
Vehicle Value Note:
Because the OM651 is typically found in W204 and W212 vehicles valued between £5,000 and £18,000, a full replacement is generally financially viable. However, 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 OM651.911/912
Explore engines that are closely related to the Mercedes-Benz OM651.911/912, including its predecessor, successor, and key family variants.
Predecessor
OM646
the 2.1L inline-4 CDI that the OM651.911/912 refined, sharing the same common-rail architecture but with improved emissions compliance and a more robust timing chain design.
Successor
OM654
the modern 2.0L inline-4 CDI successor that eventually took over the C-Class and E-Class diesel roles, delivering improved fuel economy and reduced emissions.
Sibling
OM651.924/925
the 200 CDI variant of the same OM651 family, sharing the exact same block but with lower output tuning and different ECU mapping for specific chassis applications.
Sibling
OM651.955-958
the commercial van specification of the OM651 family, featuring heavy-duty ancillary brackets and revised oil pickup tubes for Sprinter and Vito applications.
FAQ
Mercedes-Benz OM651.911/912Frequently Asked Questions
Question 1How much does a Mercedes OM651.911/912 engine replacement cost-
A reconditioned Mercedes OM651.911/912 engine typically costs between £2,800 and £4,800 for supply only . Fitted costs generally range from £3,320 to £5,580 depending on the specialist, while used units can be found from £1,500 but carry higher risk due to the timing chain tensioner issue. Compare OM651.911/912 engine replacement quotes today
Compare OM651.911/912 quotesQuestion 2What is the most common failure on the OM651.911/912 engine-
The most documented issues are timing chain tensioner wear (addressed under TSB LI80.20-P-050001), injector seal weeping ("Black Death"), and DPF/EGR clogging. The timing chain tensioner can fail and cause catastrophic valve damage if ignored, while injector seal failure causes black carbon buildup but is a cheap preventative fix. Get quotes for a rebuilt OM651.911/912 with these issues resolved
Compare OM651.911/912 quotesQuestion 3Which Mercedes models use the OM651.911/912 engine-
The OM651.911 and .912 were fitted to the W204 C-Class (C 200 CDI, C 220 CDI) and the W212 E-Class (E 200 CDI, E 220 CDI), serving as the definitive 4-cylinder diesel for these core saloons between 2008 and 2014. Check your registration to confirm your exact OM651.911/912 fitment
Compare OM651.911/912 quotesQuestion 4Should I buy a used or reconditioned OM651.911/912 engine-
A reconditioned OM651.911/912 is strongly recommended over a used unit. A proper rebuild will proactively address the fatal flaw by installing the updated timing chain tensioner, fitting new injector seals, and refreshing the EGR/DPF components, whereas a used engine with unknown history risks an immediate catastrophic chain failure. Compare reconditioned OM651.911/912 engine prices from UK specialists
Compare OM651.911/912 quotesQuestion 5How do I know if my car has the OM651.911/912 and not another OM651 variant-
The OM651.911 (typically 136 hp) and .912 (typically 170 hp) are the core saloon variants. The engine code is stamped on the right-hand side of the cylinder block above the oil filter housing and is listed on your V5C logbook. It requires specific engine mounts and ECU mapping that differ from the van-oriented .955-.958 variants. Enter your reg above to identify your exact engine code ═══════════════════════════════════════
Compare OM651.911/912 quotesCompare Mercedes-Benz OM651.911/912 Engine Prices Today
Vetted UK specialists who work on complex Mercedes CDI systems like the OM651 every week Minimum 12-month warranty on every reconditioned and rebuilt OM651.911/912 engine Nationwide delivery - supply-only or full supply & fit available across the UK Get a free, no-obligation comparison of OM651.911/912 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 the updated timing chain tensioner. With reconditioned OM651.911/912 engines starting from £2,800, comparing takes two minutes and could save you hundreds on labour and unexpected teardowns.
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Vetted UK specialists for OM651.911/912 replacements
Minimum 12-Month Warranty
Minimum 12-month warranty on reconditioned and rebuilt options
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Nationwide delivery plus supply and fit availability
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