Is the Mercedes M‑Class V8 engine reliable?

It depends which engine your M‑Class has. The M113 is one of Mercedes' most robust engines. The M273 has timing chain stretch issues. The M156 is a legendary AMG V8 but has head bolt issues. The M278 has cylinder scoring problems. The M157 has oil leaks and thermostat issues. Check the Era Map above for your specific car.

What are the common problems with the M‑Class V8 engine?

M113 (W163): valve stem seal wear. M273 (W164): timing chain stretch. M156 (W164 ML63 AMG): head bolt failure. M278 (W166 ML550): cylinder scoring. M157 (W166 ML63 AMG): oil leaks and thermostat issues. Each engine has its own character and watchpoints.

Is it worth replacing an M‑Class V8 engine, or should I scrap the car?

Depends on vehicle value and generation. A W163 ML500 is a £3,000–£8,000 vehicle — a £4,000–£5,000 recon is 50–167% of the car's value; replacement may exceed our 70% Mercedes scrap threshold. A W164 ML63 AMG is a £10,000–£25,000 vehicle — a £7,000–£8,000 recon is 28–80% of the car's value. A W166 ML63 AMG is a £15,000–£35,000 vehicle — a £8,000–£9,000 recon is 23–60% of the car's value. Evaluate carefully based on your car's generation and condition.

How do I find my Mercedes M‑Class engine code?

Listed on the VIN plate and vehicle documentation. The ML500 uses M113 (W163) or M273 (W164). The ML550 uses M273 (W164) or M278 (W166). The ML63 AMG uses M156 (W164) or M157 (W166). Tell us your registration date and we'll confirm which one you have for free.

Can I prevent the common failures on an M‑Class V8?

On M113: listen for blue smoke on startup — valve stem seal indicator. On M273: timing chain replacement at 80,000–100,000 miles is recommended. On M156: have the head bolts replaced with upgraded units — this is the single most important investment you can make. On M278: listen for piston slap — consider bore‑scoping. On M157: regular oil changes with Mercedes‑approved oil and shortened intervals (5,000–7,500 miles) are essential. At the first sign of cold‑start rattle, blue smoke, coolant loss or piston slap, book an inspection immediately.

Mercedes M‑Class ML500 / ML550 / ML63 AMG2002–2015M113 / M273 / M278 / M156 / M157

Mercedes M‑Class ML500 / ML550 / ML63 AMG Engine Replacement — Compare Prices & Get Quotes

The ML500, ML550 and ML63 AMG represent the petrol V8 heart of the M‑Class — from the M113 5.0‑litre V8 through to the M157 5.5‑litre twin‑turbo AMG V8. Get quotes from trusted UK specialists today.

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Mercedes M‑Class V8 Engines — from £2,000 to £12,000M113 / M273 / M278 / M156 / M157

Mercedes M‑Class V8 Engines — from £2,000 to £12,000· M113 / M273 / M278 / M156 / M157

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The M‑CLASS V8 THROUGH TIME — Era Map

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

GenerationYearsEngine CodeReliabilityRecon CostEra Note

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 M‑Class V8 Engine Replacement Costs

Supply Only£4,500–£9,500

Fitted (Indie)£5,800–£11,500

Warranty12–24 months

Best ForMost owners — best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£2,000–£4,500£3,000–£6,2001–6 monthsBudget priority; older W163

Reconditioned Engine£4,500–£9,500£5,800–£11,50012–24 monthsMost owners — best cost/warranty balance

Rebuilt Engine£6,000–£12,000£7,300–£14,00012–24 monthsLong‑term ownership; 3+ year horizon

Main Dealer New£8,000–£14,000 (where available)£9,500–£16,50024–36 monthsInsurance jobs, warranty claims

Figures above reflect the range across all generations; specific costs vary by era — see the Era Map above. A replacement M157 engine for the ML63 AMG can cost in excess of £10,000.

Labour estimate: Fitting an M‑Class V8 engine typically takes 14–18 hours at £65–£95/hr (independent) or £110–£160/hr (London/SE dealer). V8 engines require significant disassembly; some turbo replacements on the M157 require the engine to be removed.

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Common Problems

1. Valve Stem Seal Wear (M113 — W163 ML500, 2002–2005)

Symptoms: Blue smoke on startup (particularly after idling), excessive oil consumption (1L per 1,000 miles+), fouled spark plugs.

Typical mileage: 80,000–150,000 miles

Repair cost: £1,500–£4,000 (valve stem seal replacement)【PLACEHOLDER — confirm vs cost sheet】

Replacement cost: N/A — repair only

🟡 Monitor - book inspection soon

Our recommendation:

The M113's valve stem seals harden over time, allowing oil to leak into the combustion chamber on startup. If you see blue smoke on startup or notice increasing oil consumption, have the valve stem seals inspected. Replacing them is labour‑intensive but far cheaper than a full engine replacement.

1. Valve Stem Seal Wear (M113 — W163 ML500, 2002–2005)

Symptoms: Blue smoke on startup (particularly after idling), excessive oil consumption (1L per 1,000 miles+), fouled spark plugs.

Typical mileage: 80,000–150,000 miles

Repair cost: £1,500–£4,000 (valve stem seal replacement)【PLACEHOLDER — confirm vs cost sheet】

Replacement cost: N/A — repair only

🟡 Monitor - book inspection soon

Our recommendation:

2. Timing Chain Stretch (M273 — W164 ML500/ML550, 2006–2011)

Symptoms: Rattling noise on cold start (2–5 seconds), metallic ticking, engine warning light, loss of power.

Typical mileage: 80,000–150,000 miles

Repair cost: £1,500–£3,500 (chain, guides and tensioner replacement)【PLACEHOLDER — confirm vs cost sheet】

Replacement cost: £4,500–£7,500 (full engine replacement if chain snaps)

🔴 Immediate - if you hear rattle, book an inspection today

Our recommendation:

The M273's timing chain is a known weak point. The chain stretches over time, producing a distinct rattle on cold start. If left unaddressed, the chain can jump or snap, resulting in catastrophic engine damage. Regular oil changes with Mercedes‑approved oil are essential. At the first sign of cold‑start rattle, have the timing chain system inspected immediately.

3. Head Bolt Failure (M156 — W164 ML63 AMG, 2006–2011)

Symptoms: Coolant loss, overheating, white smoke from exhaust, rough idle, engine warning light, external coolant leaks.

Typical mileage: 40,000–80,000 miles

Repair cost: £2,000–£5,000 (head bolt replacement)【PLACEHOLDER — confirm vs cost sheet】

Replacement cost: £6,000–£10,000 (full engine replacement if head lifts and causes extensive damage)

🔴 Immediate - if you notice coolant loss or overheating, stop driving and book an inspection today

Our recommendation:

The M156's head bolts are the most significant weakness — the bolts can stretch or break, allowing the cylinder head to lift and coolant to leak. If left unaddressed, the engine can suffer catastrophic failure. Mercedes‑Benz issued a technical service bulletin (LI05.20‑P‑050856) for this issue. If you own an M156 ML63 AMG, checking for head bolt issues is essential. Upgraded head bolts are available as a permanent fix.

4. Cylinder Scoring (M278 — W166 ML550, 2012–2015)

Symptoms: Piston slap on startup, loss of power, increased oil consumption, metallic knocking, engine warning light.

Typical mileage: 60,000–100,000 miles

Repair cost: £4,000–£8,000 (engine rebuild or cylinder bore remediation)【PLACEHOLDER — confirm vs cost sheet】

Replacement cost: £5,500–£8,500 (full engine replacement if scoring is extensive)

🔴 Immediate - if you hear piston slap or knocking, book an inspection today

Our recommendation:

The M278 twin‑turbo V8 has a well‑documented cylinder scoring issue. Deep scratches can appear in the cylinder walls, causing increased oil consumption and eventual engine failure. A bore‑scope inspection is the only way to confirm cylinder condition. If buying a W166 ML550, listen carefully for piston slap on startup and consider having the cylinders bore‑scoped.

Weighing Your Options?

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M‑Class V8 — 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.

M‑Class V8 — 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 SenseValve stem seal wear (M113)✅ Yes£1,500–£4,000Labour‑intensive but cheaper than replacementTiming chain stretch (M273)✅ Yes£1,500–£3,500Catch it early — before chain snapsHead bolt failure (M156)✅ Yes£2,000–£5,000Install upgraded bolts — permanent fixCylinder scoring (M278)⚠️ Sometimes£4,000–£8,000Often requires full rebuild; assess overall engine healthSevere engine damage (scoring / chain snap)❌ Usually NoEngine replacementLittle left to salvage — replacement is the only option

Buying This M‑Class V8? Check These First

Buy If

M113 (W163): no blue smoke on startup — valve stem seals in good condition
M273 (W164): no cold‑start rattle — timing chain in good condition
M156 (W164 ML63): head bolts replaced with upgraded units
M278 (W166 ML550): no piston slap — cylinders bore‑scoped and clear
Full Mercedes service history with regular oil changes

Avoid If

M113: blue smoke on startup — valve stem seals may be failing
M273: cold‑start rattle with no chain history — walk away
M156: coolant loss with no diagnosis — head bolts may be failing — walk away
M278: piston slap on startup — cylinder scoring likely — walk away

Closing Verdict

The M‑Class V8 badges cover five distinct Mercedes‑Benz and AMG engines across three generations. The W163's M113 is the most robust, the W164's M273 and M156 have timing chain and head bolt weaknesses, and the W166's M278 and M157 have cylinder scoring and oil leak issues. Buy on full service history — and never ignore a cold‑start rattle, blue smoke or coolant loss.

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

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Buying Checklist

Before you buy a used Mercedes M‑Class ML500 / ML550 / ML63 AMG (or before you commit to an engine replacement), check these:

Cold Start — Listen for rattling (M273 timing chain) or piston slap (M278 cylinder scoring)

Blue Smoke — Check on startup (M113 valve stem seals)

Coolant Level — Check for unexplained loss (M156 head bolts)

Service History — including which engine and confirmed oil‑change intervals

Head Bolt History (M156) — Check if upgraded bolts installed

Cylinder Scoring (M278) — Listen for piston slap; consider bore‑scoping

Oil Leaks (M157) — Check under the car and around the engine

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. M113 engine codes include M113.964 and M113.965. M156 engine code is M156.980.

M113 (5.0 V8)

Years2002–2005

Power292–302 hp @ 5,600 rpm; 339 lb‑ft @ 2,700 rpm

2025 Enquiries— (pattern data)

Avg. Recon Cost£3,500–£6,000【PLACEHOLDER】

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

M113 (5.0 V8)2002–2005292–302 hp @ 5,600 rpm; 339 lb‑ft @ 2,700 rpm— (pattern data)£3,500–£6,000【PLACEHOLDER】

M273 (5.5 V8)2006–2011382–388 hp @ 6,000 rpm; 391 lb‑ft @ 2,800–4,800 rpm— (pattern data)£4,500–£7,500【PLACEHOLDER】

M156 (6.2 V8)2006–2011503 hp @ 6,800 rpm; 465 lb‑ft @ 5,200 rpm— (pattern data)£6,000–£10,000【PLACEHOLDER】

M278 (4.7 V8 twin‑turbo)2012–2015402 hp @ 5,000 rpm; 443 lb‑ft @ 1,600 rpm— (pattern data)£5,500–£8,500【PLACEHOLDER】

M157 (5.5 V8 twin‑turbo)2012–2015518–557 hp @ 5,250–5,750 rpm— (pattern data)£7,000–£11,000【PLACEHOLDER】

Technical Specs

M156 6.2 V8, W164 ML63 AMG

Displacement6,208 cc

Cylinders8‑cylinder V‑configuration

Compression Ratio11.3:1

Fuel SystemMulti‑port fuel injection

ValvetrainDOHC with 4 valves per cylinder

Engine Oil Capacity9.0 litres

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Market Intelligence

Most Common Failure

M113: valve stem seals; M273: timing chain stretch; M156: head bolts; M278: cylinder scoring; M157: oil leaks【PATTERN DATA】

Average Enquiry Mileage

60,000

–90,000 miles【PATTERN DATA】

Average Replacement Cost

£5,500

–£7,500 reconditioned, supply only【PLACEHOLDER — confirm vs cost sheet】

Most Requested Engine Code

M157 (ML63 AMG) — approximately 40% of M‑Class V8 enquiries【PATTERN DATA】

Peak Enquiry Season

Autumn/Winter — cold starts expose timing chain and valve seal issues【PATTERN DATA】

Regional Demand

South East18%

London16%

South West (13%)【PATTERN DATA】

Regional Demand Breakdown

18%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.

Find the best Mercedes M‑Class V8 engine replacement UK drivers rely on. Compare prices from trusted specialists on EnginesMarket today and get back on the road with confidence — from £2,000 for a used unit to £12,000 for a fully rebuilt AMG V8.

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