Mercedes-BenzB-Class2005–present2 GenerationsOM651OM640M270

B-Class Engines - The Complete UK Guide

Every B-Class generation covered - W245 and W246, petrol and diesel, real UK running costs and reliability data from 177+ real enquiries in 2025 [MB‑VERIFIED]. Backed by the UK's most trusted Mercedes-Benz specialist network.

Explore B-Class Engines
  • 177+ Enquiries (2025) [MB‑VERIFIED]
  • 2 Generations Covered
  • 5 Engine Codes
  • Part of Engine Finders

B-Class -
The Ownership Verdict

Verdict MetricOur Call
Overall Ownership Rating

★★★★☆

Replacement Economics

✅ The B-Class rule: generation is everything - the W246 (2011–2018) comfortably justifies replacement; the W245 (2005–2011) frequently doesn't

Reliability

★★★★☆

Most Reliable Engine

OM651 2.1 CDI - the modern diesel that powers the W246; far fewer failure reports than the earlier OM640 [MB‑VERIFIED]

Highest-Risk Engine

OM640 2.0 CDI - early W245 diesel with injector and EGR issues; pre-2008 examples particularly affected [PATTERN DATA]

Best Used Buy

W246 B200 CDI (2014–2018) - post-facelift OM651, 158‑enquiry sweet spot with £2,800–£4,800 recon cost against £5,000–£14,000 vehicle value [MB‑VERIFIED]

Average Engine Replacement

£2,800–£4,800 (recon, supply-only) [MB‑QUOTE]

Most Common Failure Enquiry

OM651 injector seal / "Black Death" - 80%+ of B-Class diesel enquiries [MB‑VERIFIED]

Mercedes Ranking

🥇 Best Family MPV - the safest, most family-friendly Mercedes in the compact segment

One-line verdict:

The B-Class is the Mercedes family MPV that genuinely makes sense - buy a post-2014 W246 with the OM651 diesel, give the early W245 petrols a miss, and you'll have a safe, affordable, long-lasting car that won't punish you at repair time.

B-Class
at a Glance

  • Generations

    2 (W245, W246)

  • Years Produced

    2005–present (2018–present: W247, omitted from core data)

  • Engine Codes Tracked

    5

  • Fuel Types

    Diesel, Petrol

  • Most Enquired Engine (2025)

    OM651 2.1 CDI - 157 enquiries (W246) [MB‑VERIFIED]

  • Most Reliable

    OM651 2.1 CDI (post-2014)

  • Highest-Risk

    OM640 2.0 CDI (pre-2008)

  • Typical Replacement Cost

    £2,800–£4,800 (recon) [MB‑QUOTE]

  • Typical Host Value

    £5,000–£14,000 (W246) / £1,500–£5,000 (W245) [THIRD‑PARTY]

Overall Rating

★★★★☆

3.9/5

A perfect blend of performance, engineering excellence, and drivability.

B-Class Generations -
Find Your Vehicle

The B-Class runs in two distinct generations - the earlier W245 (2005–2011) and the more modern W246 (2011–2018). The dividing line is sharp.

Years: 2005–2011

• Key Engines: OM640 2.0 CDI, M266 1.5/2.0 petrol, M270 1.6 turbo petrol

★★★★★
Explore W245 B-Class

Years: 2011–2018

• Key Engines: OM651 2.1 CDI (diesel), M270 1.6/2.0 petrol, M274 2.0 turbo petrol - 🔥 Most Enquired - 157 enquiries (2025) [MB‑VERIFIED]

★★★★★
Explore W246 B-Class

2019–present

• M282 petrol

★★★★★
Explore W247

B-Class Engine Codes -
The Database

Every B-Class engine code ever offered in the UK - verified against factory technical specs and cross‑referenced with real 2025 enquiry data.

Proprietary UK Data

Every figure below is powered by real UK owner enquiries in 2025. This is data you won't find anywhere else.

Engine CodeFuel2025 EnquiriesView
OM651Diesel157
M266Petrol-
M270Petrol-
M274Petrol-
OM640Diesel-

Data sources:

Enquiry volumes:
EM_Proprietary_Data_2025.txt [EM-VERIFIED]

Costs:
Table A - Engine Replacement Economics [EM-QUOTE]

Engine codes:
Cross-referenced from your existing data

Common B-ClassEngine Problems

The failures B-Class owners actually encounter - ranked by severity and backed by 177+ real UK enquiries.

01

OM651 "Black Death" Injector Seal Failure

Catastrophic if Ignored

The defining diesel issue across all OM651‑powered Mercedes models - copper injector seals degrade, allowing combustion gases to leak past and form a thick carbon "tar" around the injector base. Left untreated, the carbon can weld the injector into the cylinder head, turning a £400–£1,200 seal job into a full cylinder‑head repair or engine replacement. Most common on B‑Class W246 examples from 2012–2016 with 70,000–100,000 miles. [MB‑VERIFIED]

Read more
02

OM640 Injector & EGR Failure

Immediate

The earlier W245 diesel - injector leak‑off issues and EGR valve clogging are both common. The OM640's EU4 emissions hardware was more sensitive than the later OM651; repair costs typically £300–£800 per injector, £400–£1,200 for EGR replacement. Pre‑2008 units particularly affected [PATTERN DATA].

Read more
03

M270/M274 Turbocharger Oil Starvation

Monitor

On the 1.6‑litre and 2.0‑litre turbo petrol variants, the turbocharger's oil supply line can become restricted (sludge buildup from extended service intervals). Warning signs: high‑pitched whine under acceleration, oil consumption above 1L/1,000 miles. Typically occurs 60,000–100,000 miles [PATTERN DATA].

Read more
04

M266 Petrol Timing Chain Tensioner Wear

Monitor

The 1.5‑litre and 2.0‑litre naturally‑aspirated petrols in the W245 - timing chain tensioner wear can lead to chain rattle on cold start. Unlike the OM651's rear‑chain complexity, the M266's chain is front‑mounted, making inspection and replacement relatively straightforward. Still, if ignored, the chain can skip and the engine will need a rebuild [PATTERN DATA].

Read more
05

AdBlue System Issues (W246 facelift, 2014+)

Low

Post‑2014 W246 B‑Class with OM651 diesel - AdBlue system warnings are the most common non‑engine failure in our W246 B‑Class data. Typically NOx sensor or heater failure, software‑manageable, £400–£1,200 repair. Not a showstopper, but frustrating and needs addressing [MB‑VERIFIED].

Read more
06

DPF Clogging (Urban‑Use B‑Class)

Monitor

Both OM640 and OM651 diesels - DPF regen cycles fail to complete on short, cold urban trips. The B‑Class is often bought as a city MPV, which directly exacerbates this problem. Symptoms: limp mode, fuel‑diluted oil, £400–£1,200 for DPF clean or replacement. The fix is a 30‑minute motorway run at 2,500rpm once a month - but many owners don't know that [MB‑VERIFIED].

Read more

Urgency Key

Catastrophicstop driving, specialist inspection immediately

Immediatebook inspection now

Monitorbook inspection soon

Lowplan at next service

B - Class Market Intelligence

177++

Total Enquiries in 2025

[MB-VERIFIED]

Signal
2025 Data
Demand Trend

W246 B‑Class Enquiries

157 enquiries - the dominant B‑Class generation [MB‑VERIFIED]

Rising[PLACEHOLDER - YoY % from source data]

W245 B‑Class Enquiries

20 enquiries - lower volume, ageing‑host market [MB‑VERIFIED]

Stable[PLACEHOLDER - YoY % from source data]

OM651‑vs‑OM640 Split

88% of B‑Class enquiries are W246‑generation OM651; just 12% are W245 OM640 [MB‑VERIFIED]

Stable

Insights from the data:

Interesting insight: The B‑Class's 177 total enquiries make it one of the quieter Mercedes models in our 2025 dataset - but the 88% / 12% split between W246 and W245 is the sharpest generational divide in the entire Mercedes line‑up. Buyers are actively avoiding the first‑generation W245; the second‑generation W246 accounts for almost nine out of ten enquiries.

The OM651's "Black Death" injector‑seal failure is the single biggest driver of B‑Class diesel enquiries - but because it's a cheap, preventable fix if caught early, the OM651 is still the recommended engine. The W245's OM640 doesn't have the same known‑issue‑with‑known‑fix profile; its failures are more varied and less predictably repairable.

The B‑Class is the only Mercedes MPV that carries a ✅ Safe verdict without major caveat in our data - the V‑Class and Viano are larger and more expensive to run; the B‑Class is the genuinely family‑friendly option.

Editorial Pull-Quote

The One Thing We'd Tell Every B-Class Buyer

“Buy a W246 B‑Class from 2014 onwards with the OM651 diesel, and ignore the service‑history‑scare stories - the "Black Death" injector seal is a cheap, manageable fix if caught early. The W245 isn't necessarily a bad car, but at current market values, a new engine will cost more than the car is worth. The generation‑based advice on the B‑Class is as clear as it gets. MERCEDES B-CLASS - SECTIONS 8-14”

B-Class Engine Replacement Costs
By Generation

Real UK pricing for every B-Class engine - used, reconditioned and rebuilt options, supply-only, with independent labour guidance. All figures [MB-QUOTE].

TransparentReal UK Prices
Quality AssuredTested Engines
Fitted by ExpertsTrusted Garages
12 MonthsWarranty

W245 B-Class (2005–2011)

VariantEngine CodeUsed (Supply)Reconditioned (Supply)Rebuilt (Supply)Labour Hours
B180 CDI / B200 CDIOM640£500–£1,200£2,800–£4,800£4,000–£6,0008–10 hrs
B150 / B170 / B200M266 1.5/2.0 petrol£400–£900£1,800–£3,200£2,800–£4,5007–9 hrs
Prices are supply only. Labour and ancillary parts extra.

Important Notes

N47D20C, B47D20A, N57D30, B58B30 figures [BMW-QUOTE]; older engines [PLACEHOLDER - confirm vs cost sheet].

Labour Estimate

Fitting a B-Class engine typically takes 7–10 hours at £65–£95/hr (independent) or £110–£160/hr (London/SE dealer) [MB-QUOTE]. The B-Class rule - generation is everything: A W245 B200 CDI (OM640) at typical market value of £1,500–£5,000 against a £2,800–£4,800 recon cost sits at 56–96% - at or above our 70% threshold for many examples [THIRD-PARTY]. The honest advice: unless the car has sentimental value or a documented recent engine, walk away from a W245 diesel with a failed engine. A W246 B200 CDI (OM651) at £5,000–£14,000 against the same £2,800–£4,800 recon cost sits at 20–56% - comfortably below the threshold in most cases [MB-QUOTE]. Fix the W246; scrap the W245 (unless it's a low‑mileage, well‑kept petrol example).

The ownership rule - generation is everything:

Value the car first; the engine decision follows.

All prices in GBP (£)   •   Supply only   •   Subject to availability and condition

How the B-Class Engine Range Evolved -2005 to Today

From early petrol and diesel families through to modern powertrains - how engineering, emissions and performance shaped every generation.

7 Generations1975 to Present
25+ Engine FamiliesFrom M10 to B58
50 Years of EngineeringPerformance & Innovation
Built for DriversReliability + Dynamics

All engine reliability insights and failure patterns are based on verified UK enquiries in 2025. [MB-VERIFIED]

Who Should Buy a B-Class?

Different buyers, different priorities. Here is our verdict on who the B-Class is perfect for - and who should think twice.

Family Buyer

★★★★★

The B‑Class is the most family‑friendly compact Mercedes in our data - the W246 has the same OM651 engine as the C‑Class but with higher‑roof practicality and lower purchase prices. Buy a 2014–2018 B200 CDI, ignore the "MPV" stigma, and enjoy a safe, reliable family car that doesn't cost a fortune to run.

Daily Commuter

★★★★★

The OM651 diesel is the motorway‑mile champion - 45–55 mpg, comfortable ride, and enough power for A‑road overtakes. The B‑Class is less common than the A‑Class as a commuter car, but that means lower prices and less competition in the used market.

Budget Owner

★★★★★

This is where the generation split matters. A W245 B‑Class (2005–2011) can be bought for £1,500–£3,000, but a £2,800–£4,800 recon engine is an existential threat to the car's value - you're one failure away from scrapping it. A W246 (2011–2018) at £5,000–£8,000 is a safer budget bet - recon cost sits at 35–60% of vehicle value, which is manageable [MB‑QUOTE].

Practical Buyer

★★★★★

If you need a Mercedes badge but don't want the running costs of an E‑Class or the complexity of a GLC, the B‑Class is the sensible choice. It's the only Mercedes MPV with a ✅ Safe verdict across most examples - the V‑Class is expensive to run and the Viano is discontinued. The B‑Class is the budget‑friendly practical Mercedes.

First-Time Premium Buyer

★★★★★

The B‑Class is often someone's first Mercedes - the W246 offers the brand's quality, safety and diesel‑reliability at a price that doesn't intimidate. Buy the 2014+ OM651, budget £400–£800 for a preventative injector‑seal check, and you'll have a car that's genuinely cheaper to run than many non‑premium alternatives [EM‑INTERVIEW].

i

Real talk. The right B-Class for you depends on your budget, your mileage, and your patience for maintenance. Use the data on this page to make the right call - and avoid expensive mistakes.

Explore B-Class Engines

Can I Repair My B-Class Engine - or Should I Replace It?

The B‑Class's economics are sharply divided by generation - a W246 is almost always worth fixing; a W245 diesel often isn't.

If your W246 B‑Class has an injector‑seal failure (the most common B‑Class diesel problem in our data), a £400–£1,200 repair is a no‑brainer [MB‑VERIFIED]. But if the engine has suffered terminal bottom‑end damage (rare on the OM651), the repair‑vs‑replace decision is about to get harder - use our calculator to get a personalised verdict.

The smarter way to decide: Get a personalised repair-vs-replace verdict using real UK cost data.

Path 1

Know your engine?

Launch the diagnostic calculator with B-Class pre-selected.

Launch Diagnostic CalculatorB-Class pre-selected
  • B-Class pre-selectedAll generations covered
  • Real UK cost dataUsed, recon & rebuilt
  • Instant verdictRepair vs replace

Stop guessing. Get the right answer.

Our calculator compares real repair and replacement costs against your car's value - so you know the financially smarter move.

Start Your Verdict Now

Why B-Class Owners Trust
mercedesengine.uk

Built on Real Data

Every reliability rating and cost figure on this page is drawn from 177+ real UK B‑Class enquiries in 2025 [MB‑VERIFIED] - not manufacturer marketing, not forum guesswork.

We Tell You When Not to Repair

When a W245 B‑Class diesel's replacement cost exceeds 70% of the car's value, we say so. That's the difference between a knowledge base and a sales page - and why B‑Class owners trust us.

Vetted Mercedes

Benz Specialists - Our network of 25+ vetted Mercedes-Benz specialists includes workshops that work on B‑Class OM651 injector‑seal failures every week - they're vetted specifically for diesel‑injector diagnosis and chain work, not generalists who happen to take on Mercedes jobs.

Part of Engine Finders

mercedesengine.uk is part of the Engine Finders family, the UK's leading engine replacement marketplace - giving you the research depth of an independent authority with a vetted route to action when you need one.

B-Class Frequently Asked Questions

1

How much does a B-Class engine replacement cost in the UK?

A B‑Class engine replacement ranges from £2,800–£4,800 for a reconditioned unit (supply‑only) [MB‑QUOTE]. Labour adds 7–10 hours at £65–£95/hr independent, or £110–£160/hr at a London/SE dealer - so fitted cost is roughly £3,200–£5,800. Used engines start at £500–£1,200. The cheapest option is the W245 M266 petrol (£400–£900 used); the most expensive is the OM651 diesel recon (£2,800–£4,800). Use our calculator for a personalised quote based on your specific engine, generation and location → [/fault-diagnostic-calculator?model=b-class]
2

Which B-Class engine is the most reliable?

The OM651 2.1 CDI diesel (W246 B‑Class, 2011–2018) is the most reliable B‑Class engine in our data - it accounts for 157 of 177 total B‑Class enquiries, and the "Black Death" injector‑seal failure is a cheap, preventable fix if caught early [MB‑VERIFIED]. The M270 1.6/2.0 turbo petrol is a close second; the OM640 in the W245 is the least dependable.
3

Which B-Class engine should I avoid?

The OM640 2.0 CDI in the W245 (2005–2011) carries the highest risk - injector, EGR and DPF failures are all common, and the engine's EU4 emissions hardware is more sensitive than the OM651. More importantly, a £2,800–£4,800 recon cost frequently exceeds the £1,500–£5,000 vehicle value of a W245 B‑Class [MB‑QUOTE]. Avoid the W245 diesel unless it has a documented recent engine rebuild and you're paying sub‑£2,000 for the car.
4

Is the B-Class timing chain problem real?

On the OM651 diesel, the timing chain is front‑mounted (unlike the N47 BMW engine's rear‑chain design), so chain wear is less frequent and less catastrophic. The main OM651 caveat is the injector‑seal failure ("Black Death"), not the chain. On the M266 petrol (W245), chain tensioner wear can occur but is rare - and the chain is accessible, making inspection and replacement straightforward. If you hear a rattle on cold start from a W245 M266, have it inspected; it's unlikely to be terminal.
5

Is it worth replacing a B-Class engine?

It depends entirely on generation. A W246 B‑Class (2011–2018) is almost always worth fixing - £2,800–£4,800 recon against a £5,000–£14,000 vehicle value sits at 20–56% of value, well below our 70% threshold [MB‑QUOTE]. A W245 B‑Class (2005–2011) with a failed diesel engine is often not worth replacing - the recon cost can reach 56–96% of the car's value. Scrap it and buy a W246 instead. Use our calculator for a personalised assessment.
6

Which B-Class should I buy?

Buy a W246 B‑Class from 2014 onwards with the OM651 diesel - the post‑facelift electronics are better, the AdBlue system is software‑manageable (not a mechanical liability), and the OM651 is the most reliable B‑Class engine in our data [EM‑INTERVIEW]. Avoid the W245 diesel; the W245 petrol can be a budget‑friendly option if you're willing to accept 30–35 mpg and higher tax.
7

How do I find my B-Class engine code?

The easiest way is to check your VIN plate (visible through the windscreen or on the driver's door pillar) - the engine code is the first three characters of the engine number (e.g. "OM651" for the 2.1‑litre diesel). Alternatively, check your vehicle's registration document (V5C), which lists the engine number. If you're still unsure, use our identification tool - we'll match your VIN to the correct engine and show you the exact replacement cost → [/fault-diagnostic-calculator?model=b-class]
8

B-Class vs A-Class - which is more reliable?

The B‑Class (W246) and A‑Class (W176/W177) share the same MFA platform and the same OM651 diesel engine - reliability is identical for the engine itself. The difference is economics: the A‑Class is more common, has a wider market, and tends to hold value better; the B‑Class is a more practical, family‑friendly shape that's often cheaper to buy used. Buy on condition and generation, not badge. The W246 B‑Class's Safe verdict is one of the strongest in the Mercedes range. Read the full comparison: B‑Class vs A‑Class →

Need a head-to-head comparison?

Read our in-depth Mercedes reliability comparison guides.

Read the Full Head-to-Head

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a Decision?

Everything you need to choose with confidence.
Data. Honesty. Specialists. All in one place.

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Generations

Compare the W245 and W246 side‑by‑side, see the exact facelift changes and which engines sit in which generation.

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My Engine

Not sure if your OM651 "Black Death" is terminal or just an injector seal? Our calculator will give you a personalised repair‑vs‑replace verdict.

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UK Specialists

Get quotes from 25+ vetted Mercedes‑Benz specialists who work on B‑Class OM651 injector‑seal failures every week.

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