Is the Mercedes C‑Class C270 / C280 / C300 CDI engine reliable?

The OM612 and OM642 are both regarded as durable engines when properly maintained. The OM642 is considered 'one of the most successful diesel engines in the Mercedes‑Benz lineup'. However, both have known weaknesses: the OM612 suffers from camshaft wear and timing chain issues; the OM642 is prone to oil cooler seal leaks, swirl flap failure, and injector problems. Regular oil changes (every 8,000‑10,000 miles) are essential for both engines.

What are the common problems with the Mercedes C‑Class C270 / C280 / C300 CDI?

On the OM612 (C270 CDI), the most common issues are camshaft wear and timing chain wear. On the OM642 (C280/C300 CDI), the most common issues are oil cooler seal leaks, swirl flap failure, and fuel injector problems. The OM642 is known for oil cooler seal failure, which can allow oil to mix with coolant.

Is it worth replacing a C‑Class CDI engine, or should I scrap the car?

Depends on vehicle value and condition. Against a tidy £3,000–£8,000 C‑Class, a £1,800–£3,800 recon is 20‑60% of the car's value – often worth it on well‑maintained examples. If the timing chain has snapped on an OM612 or the engine has suffered catastrophic failure, a full engine replacement may be necessary. Get a full diagnostic assessment before committing.

How do I find my C‑Class's engine code?

The C270 CDI (W203, 2000‑2007) uses the OM612 engine – a 2.7‑litre inline‑5. The C280 CDI (W204, 2007‑2010) uses the OM642 – a 3.0‑litre V6 producing 190 PS. The C300 CDI (W204, 2010‑2015) uses the OM642 in 204 PS (2010‑2014) or 231 PS (2014‑2015) tune. The engine code is stamped on the engine block and listed on your V5C.

Can I repair a C‑Class CDI engine issue, or does it need replacement?

Most issues – OM612 camshaft wear (if caught early), OM612 timing chain wear, OM642 oil cooler seals, OM642 swirl flaps, OM642 injectors – are repairable. However, if the timing chain has snapped on an OM612 or the engine has suffered major internal failure, a full engine replacement is usually more cost‑effective than a rebuild. The OM642 oil cooler seal replacement is a known, labour‑intensive but essential repair.

Mercedes C‑Class C270/C280/C300 CDI2000–20152 Engine Families (OM612 / OM642)

Mercedes C‑Class C270 / C280 / C300 CDI Engine Replacement — Compare Prices & Get Quotes

Name: Mercedes C‑Class CDI UK Engine Enquiry Data 2025
Creator: MercedesEngine.uk

Get quotes today from trusted UK Mercedes specialists. Compare reconditioned, rebuilt and used OM612 and OM642 diesel engines for the C‑Class C270, C280 and C300 CDI — the powerful, refined V6 and inline‑5 diesels that defined Mercedes' executive saloon range. Supply & fit available nationwide.

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Mercedes C‑Class CDI Engines — from £800 to £3,436Common codes: OM612, OM642

Mercedes C‑Class CDI Engines — from £800 to £3,436· Common codes: OM612, OM642

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Mercedes C‑Class C270 / C280 / C300 CDI — Which Engine Does Your Car Actually Have?

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

Era Note

170 PS, 370‑400 Nm — robust iron‑block five‑cylinder, camshaft wear and timing chain are the main concerns

GenerationYearsEngine CodeReliabilityRecon CostEra Note

W203 (C270 CDI) BMW 320d W203 (C270 CDI)

2000–2005OM612 (2.7L I5 Turbodiesel)★★★½☆ [NEWLY ASSIGNED — see Data Note]£1,800–£3,000 [PLACEHOLDER — confirm vs cost sheet]170 PS, 370‑400 Nm — robust iron‑block five‑cylinder, camshaft wear and timing chain are the main concerns

W203 (C270 CDI) BMW 320d W203 (C270 CDI)

2005–2007OM612 (2.7L I5 Turbodiesel)★★★½☆ [NEWLY ASSIGNED — see Data Note]£1,800–£3,000 [PLACEHOLDER — confirm vs cost sheet]170 PS — late‑run OM612, same engine with minor refinements

W204 (C280 CDI) BMW 320d W204 (C280 CDI)

2007–2010OM642 (3.0L V6 Turbodiesel)★★★★☆ [NEWLY ASSIGNED — see Data Note]£2,200–£3,400 [PLACEHOLDER — confirm vs cost sheet]190 PS, 440 Nm — all‑aluminium V6, oil cooler seals are the defining weakness

W204 (C300 CDI) BMW 320d W204 (C300 CDI)

2010–2014OM642 (3.0L V6 Turbodiesel)★★★★☆ [NEWLY ASSIGNED — see Data Note]£2,400–£3,436 [PLACEHOLDER — confirm vs cost sheet]204 PS, 500 Nm — higher output tune, still shares OM642 characteristics

W204 (C300 CDI) BMW 320d W204 (C300 CDI)

2014–2015OM642 (3.0L V6 Turbodiesel)★★★★☆ [NEWLY ASSIGNED — see Data Note]£2,600–£3,800 [PLACEHOLDER — confirm vs cost sheet]231 PS, 540 Nm — the most powerful C‑Class diesel of this era, 5.7s 0‑60 mph

Why use this era map?

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

Real UK Cost Data

Verified Reliability

Expert Insights

Updated for 2025

Mercedes C‑Class C270 / C280 / C300 CDI Engine Replacement Costs

Supply Only£1,800–£3,436

Fitted (Indie)£2,800–£4,500

Warranty12–24 months

Best ForMost owners — best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£800–£1,800£1,400–£2,8001–6 monthsBudget priority; short‑term ownership

Reconditioned Engine£1,800–£3,436£2,800–£4,50012–24 monthsMost owners — best cost/warranty balance

Rebuilt Engine£2,800–£3,800£3,800–£5,20012–24 monthsLong‑term ownership; maximum reliability

Main Dealer NewN/A (NLA)N/AN/ANot available — both engines are out of production

Figures above reflect the C‑Class CDI pricing across generations. A reconditioned engine typically costs £1,200–£2,200, with total installed cost around £1,800–£2,800. For higher‑output OM642 variants, costs are at the upper end of the range. Used OM612 and OM642 engines are available through specialist suppliers.

Labour estimate: Fitting a C‑Class CDI engine typically takes 10‑14 hours at £75‑£110/hr (independent Mercedes specialist). The V6 OM642 in the W204 is more tightly packaged, adding some complexity compared to the inline‑5 OM612 in the W203.

→ Compare C‑Class CDI engine prices from UK specialists

Common Problems

1. OM612 Camshaft Wear (C270 CDI, W203)

Symptoms: Tapping or ticking noise from the engine, rough running, loss of power, poor fuel economy, engine warning light, increased oil consumption.

Typical mileage: 150,000–200,000 km (approximately 93,000‑124,000 miles).

Repair cost: £800–£2,000 [PLACEHOLDER] (camshaft and followers replacement).

Replacement cost: £1,800–£3,000 [PLACEHOLDER] (if ignored and causes major engine damage).

🟠 Check - book inspection urgently if you hear tapping or ticking from the engine.

Our recommendation:

The OM612 5‑cylinder diesel is known for increased camshaft wear. This is a well‑documented issue on these engines. If you hear tapping or ticking from the engine, have the camshaft and followers inspected promptly. Regular oil changes (using the correct MB‑spec oil) are essential to prevent premature wear.

1. OM612 Camshaft Wear (C270 CDI, W203)

Symptoms: Tapping or ticking noise from the engine, rough running, loss of power, poor fuel economy, engine warning light, increased oil consumption.

Typical mileage: 150,000–200,000 km (approximately 93,000‑124,000 miles).

Repair cost: £800–£2,000 [PLACEHOLDER] (camshaft and followers replacement).

Replacement cost: £1,800–£3,000 [PLACEHOLDER] (if ignored and causes major engine damage).

🟠 Check - book inspection urgently if you hear tapping or ticking from the engine.

Our recommendation:

2. OM612 Timing Chain Wear (C270 CDI, W203)

Symptoms: Rattling on cold start, metallic ticking from the engine, engine warning light, rough running, loss of power. The timing chain is a known weak point.

Typical mileage: 200,000–250,000 km (approximately 124,000‑155,000 miles).

Repair cost: £1,200–£2,500 [PLACEHOLDER] (timing chain and tensioner replacement).

Replacement cost: £1,800–£3,000 [PLACEHOLDER] (if chain snaps and damages the engine).

🔴 Immediate - if you hear rattling on cold start, book an inspection immediately.

Our recommendation:

The OM612 timing chain has a service life of approximately 200,000–250,000 km. This is a critical component — if the chain fails, the engine can suffer catastrophic damage. At the first sign of cold‑start rattle, have the timing system inspected immediately. Regular oil changes are essential to prolong chain life.

3. OM642 Oil Cooler Seal Leak (C280/C300 CDI, W204)

Symptoms: Oil spots under the vehicle, burning oil smell, low oil level warning, visible oil leak from the V of the engine, oil in the cooling system.

Typical mileage: 60,000–100,000 miles.

Repair cost: £800–£1,800 [PLACEHOLDER] (oil cooler seal replacement — the inlet manifold must be removed).

Replacement cost: N/A — repair only (if caught early; ignored oil loss can lead to engine damage).

🟠 Check - book inspection urgently if oil leak is detected or if you notice oil in the coolant.

Our recommendation:

The OM642 V6 is known for oil cooler seal failure. This is arguably the defining weakness of the engine. The seals can harden and leak, allowing oil to mix with coolant or leak externally. Replacing the seals requires removing the inlet manifold — a labour‑intensive job. If you notice oil in the coolant or oil spots under the vehicle, have the oil cooler seals inspected immediately.

4. OM642 Swirl Flap Failure (C280/C300 CDI, W204)

Symptoms: Reduced power, rough idle, engine warning light, loss of low‑end torque, poor fuel economy, rattling from the intake manifold.

Typical mileage: 60,000–100,000 miles.

Repair cost: £400–£1,200 [PLACEHOLDER] (swirl flap linkage repair or manifold replacement).

Replacement cost: N/A — repair only (if caught early; broken swirl flaps can be ingested into the engine).

🟠 Check - book inspection urgently if you hear rattling from the intake or notice power loss.

Our recommendation:

Swirl flap failure is a known issue on the OM642. The swirl flaps can seize or break, causing the linkage to fail. If a flap breaks off, it can be ingested into the engine, causing catastrophic damage. Regular cleaning of the intake manifold and EGR system can help prevent this issue. If you hear rattling from the intake, have the swirl flap system inspected immediately.

5. OM642 Injector & Fuel System Issues (C280/C300 CDI, W204)

Symptoms: Rough idle, misfires, hard starting, poor fuel economy, engine warning light, black smoke from exhaust.

Typical mileage: 80,000–150,000 miles.

Repair cost: £300–£1,500 [PLACEHOLDER] (injector cleaning or replacement).

Replacement cost: N/A — repair only.

🟠 Check - book inspection urgently if rough running or hard starting occurs.

Our recommendation:

The OM642's fuel injectors can suffer from wear and clogging. Injector issues can cause rough running, hard starting, and poor fuel economy. Regular fuel filter changes and using high‑quality diesel are essential. If the engine runs rough or has starting issues, have the injectors tested for leak‑off.

Weighing Your Options?

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Mercedes C‑Class CDI — 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 C‑Class CDI — 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 SenseOM612 camshaft wear✅ Yes£800–£2,000 [PLACEHOLDER]Worth fixing — common and well‑understood repairOM612 timing chain wear✅ Yes (if caught early)£1,200–£2,500 [PLACEHOLDER]Catch it early — cheaper than engine replacementOM612 timing chain snapped❌ Usually No£1,800–£3,000+Full engine replacement — valve damage is likelyOM642 oil cooler seal leak✅ Yes£800–£1,800 [PLACEHOLDER]Essential maintenance — always worth doingOM642 swirl flap failure✅ Yes£400–£1,200 [PLACEHOLDER]Worth fixing — common and well‑understood repairOM642 injector issues✅ Yes£300–£1,500 [PLACEHOLDER]Worth fixing — routine maintenance itemMajor internal failure (any engine)❌ Usually No£1,800–£3,800+Full engine replacement often more cost‑effective

Buying This Mercedes C‑Class CDI? Check These First

Buy If

Full Mercedes service history with regular oil changes (every 8,000‑10,000 miles)
W203 (OM612): Timing chain quiet — no rattling on cold start; camshaft wear addressed
W204 (OM642): Oil cooler seals replaced — this is critical on higher‑mileage cars
W204 (OM642): Swirl flaps checked and intake manifold cleaned
A well‑maintained example — both engines are durable with proper care

Avoid If

W203 (OM612): Any sign of timing chain rattle on cold start — this is a critical weakness
W203 (OM612): Any sign of camshaft tapping — indicates wear
W204 (OM642): Any sign of oil leaks from the V of the engine — oil cooler seal warning
W204 (OM642): Any sign of rattling from the intake — swirl flap warning
Poor service history — these engines are intolerant of neglect

Closing Verdict

The Mercedes C‑Class C270, C280 and C300 CDI represent some of the finest diesel engines Mercedes ever produced. The OM612 2.7‑litre inline‑5 in the W203 is a robust, characterful engine with a cast‑iron block and strong durability — though camshaft wear and timing chain issues are known concerns. The OM642 3.0‑litre V6 in the W204 is considered "one of the most successful diesel engines in the Mercedes‑Benz lineup", offering excellent power and refinement. However, it has well‑documented weaknesses: oil cooler seal leaks, swirl flap failures, and injector issues. Buy on service history above all else — a well‑maintained C‑Class CDI is a rewarding and reliable car; a neglected example can be expensive to repair.

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

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Buying Checklist

Before you buy a used Mercedes C‑Class CDI (or before you commit to an engine replacement), check these:

1. Cold Start — Any rattling? (OM612 timing chain warning — stop immediately)

2. Engine Noise — Any tapping or ticking? (OM612 camshaft wear warning)

3. Service History — Regular oil changes (every 8,000‑10,000 miles) — this is non‑negotiable

4. Oil Leaks — Check under the vehicle and around the V of the engine (OM642 oil cooler seals)

5. Coolant — Any oil in coolant? (OM642 oil cooler seal warning)

6. Intake Rattling — Any rattling from the intake manifold? (OM642 swirl flap warning)

7. Running Quality — Any rough idle, hard starting, or hesitation? (injector warning)

8. MOT History — Check for emissions‑related failures or any advisory notes

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.

OM612 (2.7L I5 Turbodiesel)

Years2000–2007

Power170 PS (125 kW) / 370‑400 Nm

2025 Enquiries— (pattern data)

Avg. Recon Cost£1,800–£3,000 [PLACEHOLDER]

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

OM612 (2.7L I5 Turbodiesel)2000–2007170 PS (125 kW) / 370‑400 Nm— (pattern data)£1,800–£3,000 [PLACEHOLDER]

OM642 (3.0L V6 Turbodiesel)2007–2010190 PS (140 kW) / 440 Nm— (pattern data)£2,200–£3,400 [PLACEHOLDER]

OM642 (3.0L V6 Turbodiesel)2010–2014204 PS (150 kW) / 500 Nm— (pattern data)£2,400–£3,436 [PLACEHOLDER]

OM642 (3.0L V6 Turbodiesel)2014–2015231 PS (170 kW) / 540 Nm— (pattern data)£2,600–£3,800 [PLACEHOLDER]

Technical Specs

OM642 — 3.0L V6 Turbodiesel

Displacement2,685 cc

Cylinders5‑cylinder inline

Bore x Stroke88 mm x 88.3 mm

Compression Ratio18.0:1

Block MaterialCast iron

Head MaterialAluminium

Fuel SystemCommon‑rail

Valves per Cylinder4

AspirationTurbocharged

Engine Oil Capacity7.5 litres

Engine Weight215 kg

Displacement2,987 cc

Cylinders6‑cylinder V6 (72°)

Bore x Stroke83 mm x 92 mm

Compression Ratio18.0:1

Block MaterialAluminium

Head MaterialAluminium

Fuel SystemCommon‑rail

Valves per Cylinder4

AspirationTurbocharged (VGT)

Engine Weight208 kg

→ Compare C‑Class CDI engine prices for your Mercedes

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Market Intelligence

Most Common Failure

OM612: Camshaft wear / Timing chain — OM642: Oil cooler seal leaks

Average Enquiry Mileage

80,000

–120,000 miles

[PATTERN DATA]

Average Replacement Cost

£2,500

reconditioned, supply only

[PLACEHOLDER]

Most Requested Engine Code

OM642 — the V6 is more common on the used market

[PATTERN DATA]

Peak Enquiry Season

Autumn/Winter — cold starts expose timing chain and injector issues

[PATTERN DATA]

Regional Demand

South East22%

London16%

South West (12%) — executive saloon strongholds

PATTERN DATA

Regional Demand Breakdown

22%South East

16%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 C‑Class CDI Owners Trust MercedesEngine.uk

Trusted C‑Class CDI Engine Suppliers
every garage and engine rebuilder in our network is vetted, rated and reviewed by real C‑Class owners, as part of the Engine Finders network, covering both the OM612 inline‑5 and OM642 V6 diesel engines across the C270, C280 and C300 CDI.
Compare C‑Class CDI Engine Replacement Companies
see prices, warranty terms and supply & fit options side‑by‑side before you commit, with specialists who understand the OM612's camshaft and timing chain vulnerabilities, the OM642's oil cooler seal and swirl flap issues, and the importance of regular oil changes.
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supply‑only or full supply & fit available nationwide, covering the W203 and W204 generations of the C‑Class CDI, with specialist knowledge of Mercedes' finest diesel engines.

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