Is the Mercedes E320 CDI or E350 CDI engine reliable?

The OM642 is considered a solid diesel overall, but it has well-documented issues. The most notorious is oil cooler seal failure — a labour-intensive repair that can cost over £2,000. Other common issues include swirl flap motor failure, exhaust manifold cracking, turbocharger problems, and glow plug breakage. The OM642 was also part of the Dieselgate scandal. With proper maintenance, these engines can be very durable.

What are the common problems with the Mercedes E320 CDI and E350 CDI?

The most frequently reported issues are oil cooler seal failure (oil leaks from the V of the engine, high labour costs), swirl flap motor failure (engine warning light P2015, power loss), exhaust manifold cracking (loss of power, turbo damage), turbocharger actuator failure, glow plug breakage (M8 threads snap on removal), and main bearing failure on pre-2009 engines. Regular maintenance using MB 229.51 spec oil is essential.

Is it worth replacing a Mercedes E-Class CDI engine, or should I scrap the car?

Depends on vehicle value and condition. Against a well-kept £8,000 E350 CDI, a £4,500 recon is 56% — approaching our 70% Mercedes threshold. Against a tired £3,500 example, the same recon exceeds the threshold — get a scrap valuation first. Well-maintained E-Class CDIs are becoming rarer — a proper restoration is often justified for a clean example.

How do I find my Mercedes E320 CDI or E350 CDI engine code?

Listed on the VIN plate and vehicle documentation. W211 (2005–2009): OM642.920 / .921. W212 (2009–2016): OM642.850 / .852 / .858. The badge on the tailgate is the easiest tell — 'E 320 CDI' or 'E 350 CDI'.

Can I repair the oil cooler seals on the OM642, or does it need full engine replacement?

Yes — oil cooler seal replacement is a well-understood but labour-intensive repair costing £800–£2,000. The oil cooler is located within the V of the engine, beneath a host of ancillary parts which need to be removed before the cooler can be accessed. The purple Viton seals last about 10–15 years or 100,000 miles. If you notice oil spots or a burning smell, have the oil cooler seals inspected immediately. Ignoring this can lead to low oil levels and potential engine damage.

Mercedes E320 CDI / E350 CDI2005–2016OM642 3.0 V6 Diesel

Mercedes E320 CDI & E350 CDI Engine Replacement — Compare Prices & Get Quotes

Name: Mercedes E320/E350 CDI UK Engine Enquiry Data 2025
Creator: MercedesEngine.uk

Get quotes today from trusted UK Mercedes E-Class specialists. Compare reconditioned, rebuilt and used OM642 3.0-litre V6 diesel engines — from the W211 to the W212 — supply & fit available nationwide.

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Mercedes E320/E350 CDI Engines — from £1,500 to £7,500Code: OM642

Mercedes E320/E350 CDI Engines — from £1,500 to £7,500· Code: OM642

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The E320 / E350 CDI THROUGH TIME — Era Map

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

Era Note

The original OM642 in the E-Class — 224 hp, 540 Nm. Smooth and torquey, but oil cooler seals and swirl flaps are known weak points.

GenerationYearsEngine CodeReliabilityRecon CostEra Note

W211 E320 CDI BMW 320d W211 E320 CDI

2005–2009OM642.920 / .921 (3.0L V6 Turbo Diesel)★★★☆☆ [NEWLY ASSIGNED — see Data Note]£3,000–£5,500 [PLACEHOLDER — confirm vs cost sheet]The original OM642 in the E-Class — 224 hp, 540 Nm. Smooth and torquey, but oil cooler seals and swirl flaps are known weak points.

W212 E350 CDI BMW 320d W212 E350 CDI

2009–2016OM642.850 / .852 / .858 (3.0L V6 Turbo Diesel)★★★½☆ [NEWLY ASSIGNED — see Data Note]£3,500–£6,000 [PLACEHOLDER]The refined OM642 — up to 265 hp, 620 Nm. More power, better efficiency, but oil cooler seals and exhaust manifold cracks remain concerns.

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 E320 / E350 CDI Engine Replacement Costs

Supply Only£3,000–£5,500

Fitted (Indie)£4,200–£7,000

Warranty12–24 months

Best ForMost owners — best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£1,500–£3,500£2,500–£4,8001–6 monthsBudget priority; vehicle under £4,000

Reconditioned Engine£3,000–£5,500£4,200–£7,00012–24 monthsMost owners — best cost/warranty balance

Rebuilt Engine£4,500–£7,500£5,700–£9,00012–24 monthsLong-term ownership; 3+ year horizon

Main Dealer NewN/AN/AN/ANo longer available from Mercedes — the OM642 is out of production

Figures above reflect the OM642 3.0-litre V6 diesel engine. A full engine replacement can cost anywhere between £1,500 and £5,000 on average, with Mercedes engine replacements typically around £3,500 or more. Reconditioned OM642 engines are available from approximately £3,000–£5,500. Main dealer new engines are no longer available.

Labour estimate: Fitting an E-Class OM642 engine typically takes 12–16 hours at £75–£110/hr (independent) or £130–£180/hr (London/SE dealer). The V6's packaging in the engine bay makes this a moderately complex job.

→ Compare E-Class diesel engine prices from UK specialists

Common Problems

1. Oil Cooler Seal Failure — The OM642's Achilles Heel

Symptoms: Oil spots under the car, burning oil smell from the engine bay, low oil level warning, oil traces in the inner V of the engine (between cylinder banks), visible oil residue around the oil cooler area.

Typical mileage: 80,000–120,000 miles (or 10–15 years)

Repair cost: £800–£2,000 (oil cooler seal replacement — labour-intensive)

Replacement cost: £3,000–£7,500 (if left untreated leads to engine damage)

🟠 Check - book inspection urgently

Our recommendation:

Oil cooler seal failure is the most notorious issue on the OM642. The oil cooler is located within the V of the engine, beneath a host of ancillary parts which need to be removed before the cooler can be accessed – hence the high labour cost. When the seals degrade, they cause lubricant to leak from the oil cooler. The purple Viton seals fitted to later engines last about 10–15 years or 100,000 miles. If you notice oil spots or a burning smell, have the oil cooler seals inspected immediately.

Read the full oil leak guide

1. Oil Cooler Seal Failure — The OM642's Achilles Heel

Typical mileage: 80,000–120,000 miles (or 10–15 years)

Repair cost: £800–£2,000 (oil cooler seal replacement — labour-intensive)

Replacement cost: £3,000–£7,500 (if left untreated leads to engine damage)

🟠 Check - book inspection urgently

Our recommendation:

Read the full oil leak guide

2. Swirl Flap Motor Failure

Symptoms: Engine warning light (P2015), poor idle, power loss, delayed acceleration, failed emissions test.

Typical mileage: 60,000–120,000 miles

Repair cost: £200–£600 (swirl flap motor replacement or bypass resistor)

Replacement cost: £3,000–£7,500 (if left untreated leads to engine damage)

🟡 Monitor - book inspection soon

Our recommendation:

The OM642's swirl flap system uses an external operating rod made of poor-quality plastic which wears prematurely. Oil can reach the servo motor through the air hose, causing failure. A common fix is a bypass resistor that fools the computer — the cheapest and easiest fix. However, if the swirl flaps themselves are damaged, intake manifold replacement may be required. If you experience power loss or an engine warning light, have the swirl flap system inspected.

Read the full swirl flap failure guide

3. Exhaust Manifold Cracking & Turbocharger Issues

Symptoms: Loss of power, unusual noises from the engine bay, rattling on cold start, turbo lag, exhaust smells in the cabin.

Typical mileage: 80,000–150,000 miles

Repair cost: £500–£1,500 (exhaust manifold replacement or turbo actuator repair)

Replacement cost: £3,000–£7,500 (if turbo failure leads to engine damage)

🟠 Check - book inspection urgently

Our recommendation:

The exhaust manifold is one of the most common weak points of the OM642. The extreme temperatures in the exhaust area can cause cracks or leaks. This can not only reduce performance but also damage the turbocharger in the long term. Workshop costs for replacement can quickly run into the thousands. The turbocharger actuator can also fail, causing bucking and loss of power. If you notice loss of power or unusual noises, have the exhaust manifold and turbocharger inspected.

Read the full turbocharger failure guide

Weighing Your Options?

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E320 / E350 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.

E320 / E350 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 SenseOil cooler seal failure✅ Yes£800–£2,000Well-understood but labour-intensive — catch it earlySwirl flap motor failure✅ Yes£200–£600Bypass resistor is cheap and effectiveExhaust manifold cracking✅ Yes£500–£1,500Catch it before it damages the turboTurbocharger actuator failure✅ Yes£300–£800Cleaning or replacement — cheaper than full turbo replacementGlow plug breakage⚠️ Sometimes£200–£1,000M8×1 threads can snap during removalMain bearing failure (pre-2009)❌ Usually No£3,000–£7,500Complete engine replacement often required

Buying This E-Class CDI? Check These First

Buy If

Full Mercedes service history with evidence of regular oil changes using MB 229.51 spec oil
Oil cooler seals replaced within the last 40,000 miles
Swirl flap motor replaced or bypassed
Post-2009 W212 preferred over early W211 (improved main bearings)
No cold-start rattle, loss of power, or oil leaks

Avoid If

Oil spots under the car or oil smell in the cabin (oil cooler seals)
Engine warning light with swirl flap or turbo codes
Loss of power or unusual exhaust noises (exhaust manifold cracks)
Poor service history — the OM642 is a sophisticated engine that demands good maintenance
Pre-2009 W211 with no history of main bearing inspection

Closing Verdict

The E320 CDI and E350 CDI are powered by Mercedes' OM642 V6 diesel — a smooth, torquey, and refined engine that served across the E-Class for over a decade. It's a solid diesel overall, but it has known weak points: oil cooler seal failure is the most notorious; swirl flap motors, exhaust manifolds, and turbochargers also demand attention. These are well-understood and manageable with proper maintenance. Buy on documented history, not on faith. A well-maintained E-Class CDI is a £5,000–£15,000 executive saloon; a neglected one is a £5,000 engine replacement waiting to happen.

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

→ Compare E-Class diesel engine prices before you buy

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

→ Compare E-Class diesel engine prices before you buy

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Buying Checklist

Before you buy a used Mercedes E320 CDI or E350 CDI (or before you commit to an engine replacement), check these:

Cold Start — Listen for rattling or unusual noises (timing chain or turbo warning)

Service History — including the OM642 era (2005–2016) and confirmed oil-change intervals using MB 229.51 spec oil

Oil Leak Check — Check for oil spots under the car or oil traces in the V of the engine (oil cooler seals)

Engine Warning Light — Have codes been read? Any swirl flap (P2015), turbo, or EGR codes?

Power Check — Test acceleration; any loss of power or lag? (turbo or exhaust manifold warning)

Smoke Check — Black smoke can indicate turbo or injector issues; white smoke can indicate coolant issues

Glow Plug Check — Any history of glow plug replacement? (M8 threads can snap on removal)

MOT History — Check for emissions-related failures

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.

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

Technical Specs

OM642

Displacement2,987 cc

CylindersV6, 72° configuration, 4 valves per cylinder

Bore x Stroke83.0 mm × 92.0 mm

Compression Ratio15.5:1 (E350 CDI)

Fuel SystemCommon-rail direct injection

TurbochargerSingle turbocharger (variable geometry)

ValvetrainDOHC

→ Compare E-Class diesel engine prices for your Mercedes

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Market Intelligence

Most Common Failure

Oil cooler seal failure — the OM642's most notorious issue; repair costs can exceed £2,000 due to labour

Average Enquiry Mileage

80,000

–120,000 miles

[PATTERN DATA]

Average Replacement Cost

£3,000

–£5,500 reconditioned, supply only

[PLACEHOLDER — confirm vs cost sheet]

Most Requested Engine Code

OM642 (E320 CDI / E350 CDI)

[PATTERN DATA]

Peak Enquiry Season

Winter — cold starts expose glow plug and timing chain issues【PATTERN DATA】

Regional Demand

London22%

South East18%

Midlands14%

PATTERN DATA

Regional Demand Breakdown

22%London

18%South East

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.

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12-Month Warranty

As standard

Nationwide Delivery

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