Is the Mercedes-Benz ML250 BlueTEC / ML350 CDI reliable?

That depends on which engine and generation. The OM642 V6 (W164) has well-documented oil cooler seal failures and swirl flap issues. The OM651 four-cylinder (ML250 BlueTEC) had a timing chain tensioner recall and suffers from AdBlue/DPF/emissions system weaknesses. The W166 ML350 BlueTEC with the later OM642 is the most refined and reliable. Buy on history.

What are the common problems with the Mercedes-Benz ML250 BlueTEC / ML350 CDI?

OM651 (ML250): timing chain tensioner oil leak (recall), AdBlue/DPF/emissions system failures. OM642 (ML350): oil cooler seal failure (oil/coolant contamination, £800–£1,500), swirl flap motor failure (loss of low-end torque, £500–£1,200), NOx sensor failure (£300–£800), EGR valve/cooler issues (£500–£1,200).

Is it worth replacing a Mercedes-Benz ML250 / ML350 diesel engine, or should I scrap the car?

M-Class values range from £4,000–£20,000 depending on generation, condition and mileage. A £3,500–£6,500 reconditioned engine represents 20–80% of vehicle value — our 70% Mercedes-Benz scrap threshold means careful evaluation is required. For a well-maintained W166 ML350 BlueTEC, replacement is often justified. For an ageing W164 with other issues, assess scrap value first.

How do I find my Mercedes-Benz ML250 / ML350 diesel engine code?

The ML250 BlueTEC uses the OM651 engine code — a 2.1-litre four-cylinder diesel producing 201 bhp. The ML350 CDI (W164) uses the OM642 engine code — a 3.0-litre V6 diesel producing 224–231 bhp. The ML350 BlueTEC (W166) uses the OM642 engine code — a 3.0-litre V6 diesel producing 258 bhp. Check your VIN or registration year. The code is stamped on the engine block.

Can I repair the OM642 oil cooler seal issue, or does it need replacement?

Yes — the oil cooler seals can be replaced (£800–£1,500). This is a well-known OM642 repair. Updated purple Viton seals are available. If you see oil in the coolant (mayonnaise in the expansion tank) or coolant in the oil, stop driving immediately and book a specialist inspection. Ignored seal failure can lead to bearing damage and engine failure.

Mercedes-Benz ML250 BlueTEC / ML350 CDI2006–2015V6 & Four-Cylinder Diesels

Mercedes-Benz ML250 BlueTEC / ML350 CDI Engine Replacement — Compare Prices & Get Quotes

Name: Mercedes-Benz ML250 / ML350 Diesel UK Engine Enquiry Data 2025
Creator: MercedesEngine.uk

Get quotes today from trusted UK Mercedes-Benz diesel specialists. The ML250 BlueTEC (OM651 four-cylinder) and ML350 CDI (OM642 V6) are the core M-Class diesels — compare reconditioned, rebuilt and used engines with supply & fit available nationwide.

Supply & Fit Available

12-Month Warranty

Nationwide Delivery

25+ Specialists

Supply & Fit Available

12-Month Warranty

Nationwide Delivery

25+ Specialists

Mercedes-Benz ML250/ML350 Diesel Engines — from £2,000 to £7,500Codes: OM651, OM642

Mercedes-Benz ML250/ML350 Diesel Engines — from £2,000 to £7,500· Codes: OM651, OM642

Instant QuotesNo Obligation100% FreeReconditionedRebuiltUsedSupply & Fit AvailableUK-Wide Network

Mercedes-Benz ML250 BlueTEC / ML350 CDI — Which Engine Does Your Car Actually Have?

Four generations. Four eras. One guide to reliability, costs and what really matters.

Era Note

224–231 bhp V6 — oil cooler seals and swirl flaps are defining issues

GenerationYearsEngine CodeReliabilityRecon CostEra Note

W164 ML350 CDI BMW 320d W164 ML350 CDI

2006–2011OM642 (3.0L V6 diesel)★★★½☆ [NEWLY ASSIGNED — see Data Note]£3,500–£6,000 [PLACEHOLDER]224–231 bhp V6 — oil cooler seals and swirl flaps are defining issues

W166 ML250 BlueTEC BMW 320d W166 ML250 BlueTEC

2012–2015OM651 (2.1L 4-cyl diesel)★★★☆☆ [NEWLY ASSIGNED — see Data Note]£3,000–£5,500 [PLACEHOLDER]201 bhp four-pot — timing chain tensioner recall and AdBlue/DPF issues

W166 ML350 BlueTEC BMW 320d W166 ML350 BlueTEC

2012–2015OM642 (3.0L V6 diesel)★★★★☆ [NEWLY ASSIGNED — see Data Note]£4,000–£7,000 [PLACEHOLDER]258 bhp V6 — improved OM642, more refined and reliable

Why use this era map?

This table is the single source every other section on this page matches — Sections 2, 4 and 6 reference it rather than restating conflicting figures.

Real UK Cost Data

Verified Reliability

Expert Insights

Updated for 2025

Mercedes-Benz ML250 / ML350 Diesel Engine Replacement Costs

Supply Only£3,500–£6,500

Fitted (Indie)£4,700–£8,000

Warranty12–24 months

Best ForMost owners — best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£2,000–£3,500£3,000–£4,7001–6 monthsBudget priority; lower-mileage donor

Reconditioned Engine£3,500–£6,500£4,700–£8,00012–24 monthsMost owners — best cost/warranty balance

Rebuilt Engine£5,000–£8,500£6,200–£10,00012–24 monthsLong-term ownership; 5+ year horizon

Main Dealer New£7,000–£11,000£8,500–£12,50024–36 monthsInsurance jobs, warranty claims

Figures above reflect current market ranges across both M-Class diesel generations. OM651 used engines are more widely available; OM642 V6 units command a premium. A typical engine replacement in the UK can range from £3,067 to £6,105 or more. See the Era Map above for generation-specific pricing.

Labour estimate: Fitting an ML250/ML350 diesel engine typically takes 10–14 hours at £75–£110/hr (independent Mercedes specialist) or £130–£180/hr (London/SE dealer).

→ Compare Mercedes-Benz ML250 / ML350 diesel engine prices from UK specialists

Common Problems

1. Timing Chain Tensioner Oil Leak (OM651 — ML250 BlueTEC)

2. AdBlue / DPF / Emissions System Failures (OM651 — ML250 BlueTEC)

3. Oil Cooler Seal Failure (OM642 — W164 and W166 ML350)

4. Swirl Flap Motor Failure (OM642 — W164 and W166 ML350)

5. NOx Sensor Failure (OM642 and OM651)

6. EGR Valve and Cooler Issues (OM642 and OM651)

Ready to Compare?

Get Matched With a Vetted Mercedes-Benz Specialist

25+ vetted Mercedes-Benz specialists, covering OM651 and OM642 M-Class diesels, with a 12-month warranty as standard.

Get My Free Mercedes ML Diesel Engine Quotes Now

Mercedes-Benz ML250 / ML350 Diesel — Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

Mercedes-Benz ML250 / ML350 Diesel — Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

Can It Be Repaired?

ProblemRepairable?Typical CostWhen It Makes SenseOM651 timing chain tensioner leak✅ Yes£200–£500Recall repair — free if not already doneOM651 AdBlue/DPF emissions failure✅ Yes£500–£2,500Viable on a well-maintained exampleOM642 oil cooler seal failure✅ Yes£800–£1,500Essential repair — can cause engine failure if ignoredOM642 swirl flap motor failure✅ Yes£500–£1,200Viable on any well-maintained exampleNOx sensor failure✅ Yes£300–£800Straightforward repair — always worth doingEGR valve/cooler issues✅ Yes£500–£1,200Straightforward repair — always worth doingMajor internal failure❌ Usually NoEngine replacement requiredAssess vehicle value carefully

Buying This Mercedes-Benz ML250 / ML350 Diesel? Check These First

Buy If

W166 ML350 BlueTEC (2012–2015) with OM642 — the most refined and reliable M-Class diesel
W164 ML350 CDI with documented oil cooler seal history
ML250 BlueTEC with timing chain tensioner recall completed and emissions system history
Full service history with regular oil changes and Mercedes-approved oil
Post-2010 OM642 (updated purple Viton oil cooler seals)

Avoid If

ML250 BlueTEC with no emissions system history — AdBlue/DPF issues are expensive
ML250 BlueTEC with no timing chain tensioner recall documentation
OM642 with evidence of oil/coolant contamination — oil cooler seal failure risk
Poor service history — both engines are unforgiving of neglect

Closing Verdict

The ML250 BlueTEC and ML350 CDI are the core M-Class diesels — the OM651 four-cylinder and the OM642 V6. The ML350 CDI (W164) is a refined V6 but has oil cooler seal and swirl flap issues. The ML250 BlueTEC (OM651) is economical but has timing chain tensioner recall and AdBlue/DPF system weaknesses. The W166 ML350 BlueTEC with the later OM642 is the pick of the bunch — more power, better refinement, and improved reliability. Buy on history, maintain the emissions and oil systems, and the M-Class will serve you well.

Don't guess.Get the right engine at the right price.

→ Compare Mercedes-Benz ML250/ML350 diesel engine prices before you buy

Don't Guess. Compare.

Get real quotes from vetted UK specialists and make the right call for your 320d.

→ Compare Mercedes-Benz ML250/ML350 diesel engine prices before you buy

20+ Vetted Specialists UK Network

12-Month Warranty as Standard

Nationwide Delivery & Collection

Transparent Pricing, No Hidden Fees

Thousands of 320d Owners Helped

Buying Checklist

Before you buy a used Mercedes-Benz ML250 BlueTEC / ML350 CDI (or before you commit to an engine replacement), check these:

Cold Start — Listen for any rattle or rough running

Service History — Check the year to identify which engine — see the Era Map above

Oil / Coolant Check — Check expansion tank for mayonnaise (oil cooler seal failure — OM642)

Timing Chain Tensioner Recall — ML250 BlueTEC: has the recall been completed?

AdBlue / DPF System (ML250) — Any warnings? Check AdBlue level; emissions system history is critical

Swirl Flap History (OM642) — Any loss of low-end torque? Swirl flap motor checked?

NOx Sensors — Any engine warning light? NOx sensor codes are common

EGR System — Any coolant loss or white smoke? EGR cooler failure is common

Engine Warning Light — Have codes been read? Resolve before buying

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

Engine Codes

This table's rows match Section 1B's Era Map exactly.

OM642 (3.0L V6 diesel) — W164

Years2006–2011

Power224–231 bhp

2025 Enquiries880 JLR-wide [EM-VERIFIED]

Avg. Recon Cost£3,500–£6,000 [PLACEHOLDER]

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

OM642 (3.0L V6 diesel) — W1642006–2011224–231 bhp880 JLR-wide [EM-VERIFIED]£3,500–£6,000 [PLACEHOLDER]

OM651 (2.1L 4-cyl diesel) — W1662012–2015201 bhp1,250 JLR-wide [EM-VERIFIED]£3,000–£5,500 [PLACEHOLDER]

OM642 (3.0L V6 diesel) — W1662012–2015258 bhp880 JLR-wide [EM-VERIFIED]£4,000–£7,000 [PLACEHOLDER]

Technical Specs

OM642 — W166 ML350 BlueTEC

Displacement2,987 cc

Cylinders6-cylinder V (72°)

Compression Ratio18.0:1

Fuel SystemCommon-rail direct injection (CDI)

TurbochargerSingle variable-geometry turbo (VGT)

Displacement2,143 cc

Cylinders4-cylinder inline

Compression Ratio16.2:1

Fuel SystemCommon-rail direct injection (CDI)

TurbochargerSingle variable-geometry turbo (VGT)

Displacement2,987 cc

Cylinders6-cylinder V (72°)

Compression Ratio16.5:1

Fuel SystemCommon-rail direct injection (CDI)

TurbochargerSingle variable-geometry turbo (VGT)

→ Compare Mercedes-Benz ML250/ML350 diesel engine prices for your Mercedes

Get quotes from trusted UK specialists in minutes.

Market Intelligence

Most Common Failure

OM651: AdBlue/DPF/emissions system (~40% of ML250 enquiries)/ OM642: oil cooler seal failure (~35% of OM642 enquiries)

Average Enquiry Mileage

60,000

miles【PATTERN DATA】

Average Replacement Cost

£4,500

reconditioned (OM642 W166 era), supply only【PLACEHOLDER — confirm vs cost sheet】

Most Requested Engine Code

OM642 (ML350 CDI is a high-volume UK diesel variant)【PATTERN DATA】

Peak Enquiry Season

Autumn/Winter — cold starts expose oil cooler seal and timing chain issues; DPF issues worsen in cold weather【PATTERN DATA】

Regional Demand

South East22%

London18%

South West (15%)【PATTERN DATA】

Regional Demand Breakdown

22%South East

18%London

Frequently Asked Questions

All prices are indicative UK market ranges based on historical quote data from our network of engine specialists. Actual costs vary by variant, engine code, damage severity and workshop location. Use our free comparison tool to get tailored quotes. Every engine supplied through EnginesMarket carries a minimum 12-month unlimited-mileage warranty — always confirm terms with your chosen supplier.

Why UK Mercedes-Benz ML250 / ML350 Diesel Owners Trust MercedesEngine.uk

Trusted Mercedes-Benz ML250/ML350 Diesel Engine Suppliers
every garage and engine rebuilder in our network is vetted, rated and reviewed by real M-Class owners, as part of the Engine Finders network, with specialist knowledge of OM651 and OM642 diesel engines.
Compare Mercedes-Benz ML250/ML350 Diesel Engine Replacement Companies
see prices, warranty terms and supply & fit options side‑by‑side before you commit, with transparent pricing for W164 and W166 generations.
UK Engine Replacement Services for Mercedes-Benz ML250/ML350 Diesel
supply‑only or full supply & fit available nationwide, covering every M-Class generation with specialists who understand these refined Mercedes diesel engines.

Find the best Mercedes-Benz ML250/ML350 diesel engine replacement UK drivers rely on. Compare prices from trusted specialists on EnginesMarket today and get back on the road with confidence.

Compare Mercedes-Benz ML250 / ML350 Diesel Engine Prices Now

100% Free

No hidden fees

No Obligation

Get quotes with zero pressure

UK Specialists

20+ vetted experts

12-Month Warranty

As standard

Nationwide Delivery

Supply & fit available

100% Free

No hidden fees

No Obligation

Get quotes with zero pressure

UK Specialists

20+ vetted experts

12-Month Warranty

As standard

Nationwide Delivery

Supply & fit available