What are the common problems with the Mercedes S‑Class S300 / S320 diesel?

On the OM603 and OM606 (W140), the most common issue is timing chain stretch – causing rattling on cold start. On the OM648 (W220), common issues include injector seal failure and EGR valve problems. On the OM642 (W221), the defining weakness is oil cooler seal leaks. All engines can suffer from DPF blockage on urban‑only vehicles and fuel injector issues at high mileage.

Is it worth replacing an S‑Class diesel engine, or should I scrap the car?

Depends on vehicle value and condition. Against a tidy £4,000–£10,000 S‑Class, a £2,200–£4,500 recon is 20‑60% of the car's value – often worth it on well‑maintained examples. If the timing chain has snapped on an OM603/OM606 or the engine has suffered catastrophic failure, a full engine replacement may be necessary. Get a full diagnostic assessment before committing. The W140 S‑Class is becoming a modern classic, so well‑preserved examples may justify the investment.

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

The W140 (1993‑1996) S350 TD uses the OM603.971 – a 3.5‑litre inline‑six. The W140 (1996‑1998) S300 TD uses the OM606.961 – a 3.0‑litre inline‑six. The W220 (2002‑2005) S320 CDI uses the OM648.960 – a 3.2‑litre inline‑six. The W221 (2006‑2013) S320 CDI uses the OM642.932 – a 3.0‑litre V6. The engine code is stamped on the engine block and listed on your V5C.

Can I repair an S‑Class diesel engine issue, or does it need replacement?

Most issues – OM603/OM606 timing chain wear (if caught early), OM648 injector/EGR issues, OM642 oil cooler seals – are repairable. However, if the timing chain has snapped on an OM603/OM606 or the engine has suffered major internal failure, a full engine replacement is usually more cost‑effective than a rebuild.

Mercedes S‑Class S300 / S320 Diesel1993–20133 Engine Families

Mercedes S‑Class S300 / S320 Diesel Engine Replacement — Compare Prices & Get Quotes

Name: Mercedes S‑Class S300/S320 Diesel UK Engine Enquiry Data 2025
Creator: MercedesEngine.uk

Get quotes today from trusted UK Mercedes specialists. Compare reconditioned, rebuilt and used OM603, OM606, OM648 and OM642 diesel engines for the S‑Class S300 and S320 — the legendary, durable straight‑six and V6 diesels that powered Mercedes' flagship for two decades. 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 S‑Class S300/S320 Diesel Engines — from £1,500 to £4,500Common codes: OM603, OM606, OM648, OM642

Mercedes S‑Class S300/S320 Diesel Engines — from £1,500 to £4,500· Common codes: OM603, OM606, OM648, OM642

Instant QuotesNo Obligation100% FreeReconditionedRebuiltUsedSupply & Fit AvailableUK‑Wide Network

Mercedes S‑Class S300 / S320 Diesel — Which Engine Does Your Car Actually Have?

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

Era Note

150 PS, 330 Nm — cast‑iron SOHC 2‑valve, legendary durability, timing chain stretch is the main concern

GenerationYearsEngine CodeReliabilityRecon CostEra Note

W140 (S 350 TD) BMW 320d W140 (S 350 TD)

1993–1996OM603.971 (3.5L I6 Turbodiesel)★★★★☆ [NEWLY ASSIGNED — see Data Note]£2,000–£3,500 [PLACEHOLDER — confirm vs cost sheet]150 PS, 330 Nm — cast‑iron SOHC 2‑valve, legendary durability, timing chain stretch is the main concern

W140 (S 300 TD) BMW 320d W140 (S 300 TD)

1996–1998OM606.961 (3.0L I6 Turbodiesel)★★★★½☆ [NEWLY ASSIGNED — see Data Note]£2,200–£3,800 [PLACEHOLDER — confirm vs cost sheet]177 PS, 330 Nm — DOHC 4‑valve evolution, one of the best diesel engines ever, timing chain stretch at high mileage

W220 (S 320 CDI) BMW 320d W220 (S 320 CDI)

2002–2005OM648.960 (3.2L I6 Turbodiesel)★★★★☆ [NEWLY ASSEND — see Data Note]£2,500–£4,200 [PLACEHOLDER — confirm vs cost sheet]204 PS, 500 Nm — common‑rail I6, smooth and torquey, injector and EGR issues are the main concerns

W221 (S 320 CDI) BMW 320d W221 (S 320 CDI)

2006–2013OM642.932 (3.0L V6 Turbodiesel)★★★☆☆ [NEWLY ASSIGNED — see Data Note]£2,800–£4,500 [PLACEHOLDER — confirm vs cost sheet]235‑240 PS, 540 Nm — V6 CDI, oil cooler seal leaks are the defining weakness

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 S‑Class S300 / S320 Diesel Engine Replacement Costs

Supply Only£2,200–£4,000

Fitted (Indie)£3,200–£5,500

Warranty12–24 months

Best ForMost owners — best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£1,500–£2,800£2,500–£4,0001–6 monthsBudget priority; short‑term ownership

Reconditioned Engine£2,200–£4,000£3,200–£5,50012–24 monthsMost owners — best cost/warranty balance

Rebuilt Engine£3,000–£4,500£4,200–£6,20012–24 monthsLong‑term ownership; maximum reliability

Main Dealer NewN/A (NLA for older engines)N/AN/AOM603/OM606 no longer available new; OM648/OM642 limited availability

Figures above reflect the S‑Class diesel pricing across generations. A reconditioned S‑Class diesel engine typically costs £2,200–£4,000 supply only depending on engine generation. OM603 and OM606 engines are generally more affordable due to their simpler construction; OM648 and OM642 engines command a premium. Mercedes-Benz S‑Class engines are listed at around £2,371. Labour costs for engine replacement typically range from £800 to £2,500.

Labour estimate: Fitting an S‑Class diesel engine typically takes 10‑16 hours at £75‑£110/hr (independent Mercedes specialist). The S‑Class's longitudinal engine layout and extensive under‑bonnet packaging add complexity. The V6 OM642 in the W221 is more tightly packaged than the inline‑six engines.

→ Compare S‑Class diesel engine prices from UK specialists

Common Problems

1. OM603 / OM606 Timing Chain Stretch (W140, 1993–1998)

Symptoms: Rattling noise on cold start, metallic ticking from the engine, engine warning light, rough running, loss of power. The timing chain can stretch significantly over time — at 4 degrees of stretch it should be replaced. Some engines have suffered catastrophic timing chain failure, with valvetrain damage and internal components colliding.

Typical mileage: 150,000–200,000 km (93,000–124,000 miles) — chain stretch becomes dangerous from 150,000–200,000 km.

Repair cost: £800–£2,000 [PLACEHOLDER] (timing chain, guides, and tensioner replacement).

Replacement cost: £2,200–£3,800 [PLACEHOLDER] (if chain snaps and damages the engine).

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

Our recommendation:

The timing chain on OM603 and OM606 engines is a known wear item. Mercedes recommends checking injection pump timing every 30,000‑60,000 miles. The chain can stretch up to 4 degrees before requiring replacement. If the chain breaks, it can cause catastrophic valvetrain damage. A preventative chain replacement is far cheaper than a full engine replacement. At the first sign of cold‑start rattle, have the timing system inspected immediately. Regular oil changes are essential to prolong chain life.

1. OM603 / OM606 Timing Chain Stretch (W140, 1993–1998)

Typical mileage: 150,000–200,000 km (93,000–124,000 miles) — chain stretch becomes dangerous from 150,000–200,000 km.

Repair cost: £800–£2,000 [PLACEHOLDER] (timing chain, guides, and tensioner replacement).

Replacement cost: £2,200–£3,800 [PLACEHOLDER] (if chain snaps and damages the engine).

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

Our recommendation:

2. OM648 Injector & EGR Valve Issues (W220 S320 CDI, 2002–2005)

Symptoms: Rough idle, hard starting, misfires, poor fuel economy, engine warning light, black smoke from exhaust, engine stalling. MB injector bottom seals are prone to fail — if there is moisture or something black on the feet of the injector, it is an early stage symptom. The EGR valve can also become clogged, causing bad running and boost issues.

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

Repair cost: £400–£1,200 [PLACEHOLDER] (injector seal replacement or EGR valve cleaning/replacement).

Replacement cost: N/A — repair only.

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

Our recommendation:

The OM648's injector bottom seals are prone to failure, allowing combustion gases to leak past. This can cause rough running, hard starting, and misfires. The EGR valve can also become clogged with soot, particularly on vehicles used for short journeys. Regular use of quality diesel and occasional fuel system cleaner can help prevent injector issues. If the engine runs rough or has starting issues, have the injector seals and EGR system inspected.

3. OM642 Oil Cooler Seal Leaks (W221 S320 CDI, 2006–2013)

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. The OM642 V6 is known for oil cooler seal failure — this is arguably the defining weakness of the engine.

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. 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. OM648 Engine Noise, Vibration & Harshness (NVH) — Harmonic Balancer

Symptoms: Loud, low‑pitch booming, growling, rasping or droning noise from the engine, resonance in the cabin, particularly when starting from cold and under load.

Typical mileage: 100,000–150,000 miles.

Repair cost: £300–£800 [PLACEHOLDER] (crankshaft harmonic balancer pulley replacement).

Replacement cost: N/A — repair only.

🟡 Monitor - book inspection soon if symptoms develop.

Our recommendation:

The OM648 inline‑six can develop significant NVH issues. A worn or damaged crankshaft harmonic balancer pulley can cause excessive engine NVH. Some owners have reported the issue defying diagnosis by multiple specialists. If you notice unusual booming or droning noises from the engine, have the harmonic balancer inspected.

5. OM648 / OM642 Fuel Injector Failure & DPF Blockage

Symptoms: Rough idle, misfires, hard starting, poor fuel economy, engine warning light, black smoke from exhaust, reduced power, DPF warning light. Diesel S‑Class engines with over 200,000 miles may have further problems including diesel fuel injector failure, EGR valve issues, and problems with the diesel particulate filters (DPF) clogging up over time.

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

Repair cost: £400–£1,500 [PLACEHOLDER] (injector cleaning/replacement or DPF cleaning/replacement).

Replacement cost: N/A — repair only.

🟠 Check - book inspection urgently if rough running or warning lights appear.

Our recommendation:

Both the OM648 and OM642 can suffer from injector failure and DPF blockage over time. DPF blockage is particularly common on vehicles used primarily for short journeys or urban driving. Regular motorway runs (30+ minutes at 60+ mph) are essential to maintain the exhaust filtration system. Fuel injector failure can cause rough running, misfires, and hard starting. If you experience any of these symptoms, have the injectors and DPF system inspected.

Weighing Your Options?

Compare Specialist Quotes When You're Ready

25+ vetted Mercedes specialists, covering the OM603, OM606, OM648 and OM642 engines across the S‑Class S300 and S320 diesel, with a 12‑month warranty as standard.

See S‑Class Diesel Engine Options

Mercedes S‑Class S300 / S320 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 S‑Class S300 / S320 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 SenseOM603/OM606 timing chain stretch✅ Yes (if caught early)£800–£2,000 [PLACEHOLDER]Catch it early — cheaper than engine replacementOM603/OM606 timing chain snapped❌ Usually No£2,200–£3,800+Full engine replacement — valvetrain damage is likelyOM648 injector seals / EGR issues✅ Yes£400–£1,200 [PLACEHOLDER]Worth fixing — common and well‑understood repairOM642 oil cooler seal leaks✅ Yes£800–£1,800 [PLACEHOLDER]Essential maintenance — always worth doingOM648 harmonic balancer issues✅ Yes£300–£800 [PLACEHOLDER]Worth fixing — resolves NVH issuesOM648/OM642 injector / DPF issues✅ Yes£400–£1,500 [PLACEHOLDER]Worth fixing — common on high‑mileage dieselsMajor internal failure (any engine)❌ Usually No£2,200–£4,500+Full engine replacement often more cost‑effective

Buying This Mercedes S‑Class S300 / S320 Diesel? Check These First

Buy If

Full Mercedes service history with regular oil changes (every 8,000‑10,000 miles)
W140 (OM603/OM606): Timing chain quiet — no rattling on cold start
W220 (OM648): Injectors in good health — no hard starting or rough idle
W221 (OM642): Oil cooler seals replaced — this is critical on higher‑mileage cars
A well‑maintained example — the OM603 and OM606 are legendary for their durability

Avoid If

W140 (OM603/OM606): Any sign of timing chain rattle on cold start — this is a critical weakness
W220 (OM648): Any sign of injector issues — rough running or hard starting
W221 (OM642): Any sign of oil leaks from the V of the engine — oil cooler seal warning
Any sign of DPF warnings or emissions issues — indicates urban‑only driving
Poor service history — these engines are intolerant of neglect

Closing Verdict

The Mercedes S‑Class S300 and S320 diesel models represent three generations of some of the finest diesel engines Mercedes ever produced. The OM603 and OM606 in the W140 are legendary for their durability — the OM606 is considered "one of the best passenger diesel engines ever". The OM648 in the W220 is a smooth, torquey common‑rail inline‑six with a strong reputation. The OM642 in the W221 is a refined V6 but has a well‑documented oil cooler seal weakness. Buy on service history above all else — a well‑maintained S‑Class diesel is a rewarding and exceptionally durable car; a neglected example can be expensive to repair.

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

→ Compare S‑Class 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 S‑Class 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 S‑Class S300 / S320 diesel (or before you commit to an engine replacement), check these:

1. Cold Start — Any rattling? (OM603/OM606 timing chain warning — stop immediately)

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

3. Timing Chain History — W140 (OM603/OM606): Has the chain been inspected or replaced?

4. Injector Health — Any hard starting, rough idle, or misfires? (injector warning)

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

6. EGR System — Any engine warning lights? Any EGR‑related codes?

7. DPF Health — Has the vehicle done regular longer runs? (short trips kill DPFs)

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.

OM603.971 (3.5L I6 Turbodiesel)

Years1993–1996

Power150 PS (110 kW) / 330 Nm

2025 Enquiries— (pattern data)

Avg. Recon Cost£2,000–£3,500 [PLACEHOLDER]

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

OM603.971 (3.5L I6 Turbodiesel)1993–1996150 PS (110 kW) / 330 Nm— (pattern data)£2,000–£3,500 [PLACEHOLDER]

OM606.961 (3.0L I6 Turbodiesel)1996–1998177 PS (130 kW) / 330 Nm— (pattern data)£2,200–£3,800 [PLACEHOLDER]

OM648.960 (3.2L I6 Turbodiesel)2002–2005204 PS (150 kW) / 500 Nm— (pattern data)£2,500–£4,200 [PLACEHOLDER]

OM642.932 (3.0L V6 Turbodiesel)2006–2013235‑240 PS / 540 Nm— (pattern data)£2,800–£4,500 [PLACEHOLDER]

Technical Specs

OM642.932 — 3.0L V6 Turbodiesel

Displacement3,449 cc

Cylinders6‑cylinder inline

ValvetrainSOHC, 2 valves per cylinder

Block MaterialCast iron

Fuel SystemIndirect injection

Compression Ratio22.0:1

Displacement2,996 cc

Cylinders6‑cylinder inline

Bore x Stroke87 mm x 84 mm

ValvetrainDOHC, 4 valves per cylinder

Block MaterialCast iron

Head MaterialAluminium

Fuel SystemIndirect injection

Compression Ratio22.0:1 (turbo)

Dry Weight210 kg

Displacement3,222 cc

Cylinders6‑cylinder inline

Fuel SystemCommon‑rail direct injection

Power204 PS (150 kW) at 4,200 rpm

Torque500 Nm from 1,800‑2,600 rpm

Displacement2,987 cc

Cylinders6‑cylinder V6

Fuel SystemCommon‑rail direct injection

Power235‑240 PS (170 kW)

Torque540 Nm

→ Compare S‑Class diesel engine prices for your Mercedes

Get quotes from trusted UK specialists in minutes.

Market Intelligence

Most Common Failure

OM603/OM606: Timing chain stretch — OM648: Injector/EGR issues — OM642: Oil cooler seal leaks

Average Enquiry Mileage

80,000

–120,000 miles

[PATTERN DATA]

Average Replacement Cost

£3,000

reconditioned, supply only

[PLACEHOLDER]

Most Requested Engine Code

OM606 — the legendary 3.0L straight‑six is most sought‑after

[PATTERN DATA]

Peak Enquiry Season

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

[PATTERN DATA]

Regional Demand

South East22%

London18%

South West (12%) — flagship saloon strongholds

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 S‑Class S300 / S320 Diesel Owners Trust MercedesEngine.uk

Trusted S‑Class Diesel Engine Suppliers
every garage and engine rebuilder in our network is vetted, rated and reviewed by real S‑Class owners, as part of the Engine Finders network, covering the legendary OM603 and OM606 straight‑six diesels, the OM648 common‑rail, and the OM642 V6 diesel across three generations of the flagship S‑Class.
Compare S‑Class Diesel Engine Replacement Companies
see prices, warranty terms and supply & fit options side‑by‑side before you commit, with specialists who understand the OM603/OM606's timing chain vulnerabilities, the OM648's injector and EGR issues, the OM642's oil cooler seal weaknesses, and the importance of regular oil changes.
UK Engine Replacement Services for the S‑Class
supply‑only or full supply & fit available nationwide, covering the W140, W220 and W221 generations of the S300 and S320 diesel, with specialist knowledge of Mercedes' most durable and refined diesel engines.

Find the best Mercedes S‑Class S300 / S320 diesel engine replacement UK drivers rely on. Compare prices from trusted specialists on EnginesMarket today and get back behind the wheel of the flagship saloon with confidence.

Explore Mercedes S‑Class Diesel Engine Quotes

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