Is the Mercedes‑Benz CLK55 / CLK63 AMG engine reliable?

It depends on which engine you're asking about. The M113 (CLK55) has a legendary 'bulletproof' reputation, but age takes its toll: rear crank seal leaks, valve cover gaskets, and coil pack failures are common. The M156 (CLK63) is a masterpiece of engineering but has well‑documented weaknesses: cylinder head bolt failure, camshaft lobe and valve lifter wear, and valve train noise. Regular maintenance is absolutely essential.

What are the common problems with the Mercedes‑Benz CLK55 / CLK63 AMG?

CLK55 (M113): rear crank seal leaks, valve cover and breather leaks, coil pack and MAF sensor failures. CLK63 (M156): cylinder head bolt failure, camshaft adjuster and valve train wear, valve bucket 'bleed down' causing cold‑start tapping, crankcase breather valve failure, oil leaks, and thermostat failures. See the Era Map above for generation‑specific advice.

Is it worth replacing a CLK55 / CLK63 AMG engine, or should I scrap the car?

Depends on vehicle value. Against a well‑kept CLK63 AMG (values £15,000–£35,000+), a £6,000–£8,000 reconditioned engine is 20–50% of the vehicle's value — often worth it. The CLK55 AMG (values £8,000–£20,000+) makes a £4,000–£5,500 recon a 25–50% investment. Given the CLK AMG's status as a future classic and rising values, engine replacement is often worth it for a good example.

How do I find my Mercedes‑Benz CLK55 / CLK63 AMG engine code?

The engine code (M113.987 or M156) is listed on the VIN plate and vehicle documentation. The CLK55 AMG (2003–2005) uses the M113.987 5.4‑litre V8 producing 362 bhp. The CLK63 AMG (2006–2009) uses the M156 6.2‑litre V8 producing 475 bhp. Tell us your registration and we'll confirm for free.

Can I repair the M156 head bolts, or does it require engine replacement?

Yes — if caught early. A preventative head bolt replacement with updated ARP studs costs £2,000–£5,000 and is widely considered essential preventative maintenance on the M156. However, if the head bolts have failed and caused cylinder head damage, a full engine replacement may be required. If you're buying a CLK63 AMG, check whether this work has been done.

Mercedes‑Benz CLK55 / CLK63 AMG2003–2009M113 / M156 V8

Mercedes‑Benz CLK55 / CLK63 AMG Engine Replacement — Compare Prices & Get Quotes

Name: Mercedes‑Benz CLK55 / CLK63 AMG UK Engine Enquiry Data 2025
Creator: MercedesEngine.uk

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Mercedes‑Benz CLK55 / CLK63 AMG Engines — from £3,000 to £12,000Common codes: M113, M156

Mercedes‑Benz CLK55 / CLK63 AMG Engines — from £3,000 to £12,000· Common codes: M113, M156

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The CLK55 / CLK63 AMG THROUGH TIME — Era Map

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

Era Note

Hand‑assembled 5.4‑litre V8 — "bulletproof" reputation but rear crank seal, valve cover leaks and coil packs are the key watchpoints

GenerationYearsEngine CodeReliabilityRecon CostEra Note

CLK55 AMG (C209/A209) BMW 320d CLK55 AMG (C209/A209)

2003–2005M113.987 (5.4L V8, 362 bhp)★★★★½ [NEWLY ASSIGNED — see Data Note]£4,000–£7,500 [PLACEHOLDER — confirm vs cost sheet]Hand‑assembled 5.4‑litre V8 — "bulletproof" reputation but rear crank seal, valve cover leaks and coil packs are the key watchpoints

CLK63 AMG (C209/A209) BMW 320d CLK63 AMG (C209/A209)

2006–2009M156 (6.2L V8, 475 bhp)★★★☆☆ [NEWLY ASSIGNED — see Data Note]£6,000–£12,000 [PLACEHOLDER — confirm vs cost sheet]AMG's first clean‑sheet V8 — 475 bhp, 7200 rpm redline; head bolt failure, camshaft lobe wear and valve train noise are well‑documented weaknesses

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 CLK55 / CLK63 AMG Engine Replacement Costs

Supply Only£4,500–£8,500

Fitted (Indie)£5,800–£10,000

Warranty12–24 months

Best ForMost owners — best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£3,000–£5,500£4,000–£7,0001–6 monthsBudget priority; finding a good donor M113/M156 is becoming harder

Reconditioned Engine£4,500–£8,500£5,800–£10,00012–24 monthsMost owners — best cost/warranty balance

Rebuilt Engine£6,000–£12,000£7,500–£13,50012–24 monthsLong‑term ownership; full factory‑spec refresh

Main Dealer NewN/A — unavailableN/A—M113 and M156 engines are no longer produced new; reconditioned units are the standard

Figures above reflect the CLK55/CLK63 AMG era (2003–2009). A CLK63 AMG engine replacement can cost approximately £4,000–£8,000 from a specialist. One owner reported a quote of £8,000 for a fitted engine, with a used M156 engine and transmission available from around £4,100.

Labour estimate: Fitting a CLK AMG engine typically takes 12–16 hours at £85–£130/hr (independent) or £140–£200/hr (London/SE dealer). The V8's size and complexity add significant labour. [PLACEHOLDER — confirm vs cost sheet]

→ Compare CLK55 / CLK63 AMG engine prices from UK specialists

Common Problems

1. M156 Cylinder Head Bolt Failure (CLK63 AMG)

Symptoms: Coolant loss, overheating, white smoke from exhaust, check engine light, loss of power, misfires, potential catastrophic engine failure.

Typical mileage: 30,000–80,000 miles (can occur at any mileage)

Repair cost: £2,000–£5,000 (head bolt replacement with updated ARP studs — often requires cylinder head removal)【PLACEHOLDER】

Replacement cost: £6,000–£12,000 (if failure leads to engine damage)【PLACEHOLDER】

🔴 Immediate - if you notice coolant loss or overheating, stop driving immediately

Our recommendation:

The M156's cylinder head studs can stretch, allowing the cylinder head to lift slightly and causing coolant to leak into the combustion chamber or oil passages. This is the single biggest reliability concern on the CLK63 AMG. Symptoms include coolant loss, overheating, white smoke, and engine damage. If you suspect head bolt issues, have a leak‑down test performed immediately. Many owners proactively replace the factory head bolts with updated ARP studs to prevent failure. If you're buying a CLK63, check whether this work has been done.

1. M156 Cylinder Head Bolt Failure (CLK63 AMG)

Symptoms: Coolant loss, overheating, white smoke from exhaust, check engine light, loss of power, misfires, potential catastrophic engine failure.

Typical mileage: 30,000–80,000 miles (can occur at any mileage)

Repair cost: £2,000–£5,000 (head bolt replacement with updated ARP studs — often requires cylinder head removal)【PLACEHOLDER】

Replacement cost: £6,000–£12,000 (if failure leads to engine damage)【PLACEHOLDER】

🔴 Immediate - if you notice coolant loss or overheating, stop driving immediately

Our recommendation:

2. M113 Rear Crank Seal & Valve Cover Leaks (CLK55 AMG)

Symptoms: Oil spots under the vehicle, burning oil smell, low oil warning, visible oil seepage around the rear of the engine or valve covers.

Typical mileage: 60,000–120,000 miles

Repair cost: £400–£1,200 (valve cover gaskets) · £800–£2,000 (rear crank seal — requires transmission removal)【PLACEHOLDER】

Replacement cost: N/A — repair only (unless oil starvation leads to engine damage)

🟡 Monitor - book inspection soon; oil leaks can damage other components

Our recommendation:

The rear crank seal is a very common issue on the M113. Both valve cover and breather leaks are also common — they "do drip into unexpected places". One owner reported that after replacing the rear crank seal, it started leaking again within 6–8 months until a modified seal arrangement was used. If you notice oil spots under the car or a burning smell, have the system inspected promptly. The valve cover and breather leaks are "cheap enough to fix".

3. M156 Camshaft Adjuster & Valve Train Wear (CLK63 AMG)

Symptoms: Loud tapping or rattling noise on cold start, rough idling, engine knocking noises especially on startup, reduced engine performance, check engine light.

Typical mileage: 40,000–80,000 miles

Repair cost: £1,500–£4,000 (camshaft adjuster repair or replacement)【PLACEHOLDER】

Replacement cost: £6,000–£12,000 (if failure leads to valve train damage)【PLACEHOLDER】

🔴 Immediate - if you hear tapping or rattling, book an inspection today

Our recommendation:

The M156 is known for accelerated wear in the valvetrain, with valve buckets prone to "bleed down" resulting in excessive valve lash during cold start — commonly heard as a loud tapping noise until the engine reaches operating temperature. Early production engines have noisy valve "buckets", cam wear issues, and head bolts that just aren't able to endure sustained performance driving. If you hear unusual noises from the top of the engine, have the valvetrain inspected immediately.

4. M113 Coil Pack & MAF Sensor Failure (CLK55 AMG)

Symptoms: Misfires, loss of power, rough running, check engine light, poor fuel economy.

Typical mileage: 60,000–100,000 miles

Repair cost: £200–£600 (coil pack replacement) · £100–£300 (MAF sensor replacement)【PLACEHOLDER】

Replacement cost: N/A — repair only

🟡 Monitor - book inspection soon; can affect drivability and fuel economy

Our recommendation:

Coil packs and MAF sensors "can be an issue" on the M113. The M113 is generally bulletproof as long as it is serviced properly, but these sensors can fail over time. If you experience misfires or rough running, have the ignition system and MAF sensor inspected. Replace all coil packs preventatively to avoid catalytic converter damage from prolonged misfires.

5. M156 Thermostat & Cooling System Issues (CLK63 AMG)

Symptoms: Engine fan constantly running on high, coolant temperature error message on dash, vehicle taking longer than usual to get to operating temperature.

Typical mileage: 40,000–80,000 miles

Repair cost: £300–£800 (thermostat replacement)【PLACEHOLDER】

Replacement cost: N/A — repair only (unless overheating leads to engine damage)

🟠 Check - book inspection urgently if cooling system warnings appear

Our recommendation:

Thermostat failure on the M156 can range from minor annoyances to critical issues. The most prevalent symptoms include the engine fan running constantly, dashboard temperature warnings, and slow warm‑up. If you notice any of these, have the cooling system inspected promptly to prevent more serious issues.

6. M156 Crankcase Breather Valve Failure (CLK63 AMG)

Symptoms: Increased oil consumption, misfires, heavy smoke from tailpipe, check engine light (P0170), rough running.

Typical mileage: 60,000 miles (recommended maintenance interval)

Repair cost: £200–£500 (breather valve replacement)【PLACEHOLDER】

Replacement cost: N/A — repair only (unless oil starvation leads to engine damage)

🟡 Monitor - book inspection soon; can lead to increased oil consumption and misfires

Our recommendation:

The M156's crankcase breather valve is a common failure point. The diaphragm on the valve deteriorates, or the hose from the crankcase becomes brittle and cracks. This leads to increased oil burning, misfires, and heavy smoke. A maintenance interval of around 60,000 miles is recommended for replacement. The job involves removing the intake manifold and takes about 30 minutes.

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Mercedes‑Benz CLK55 / CLK63 AMG — 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 CLK55 / CLK63 AMG — 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 SenseM113 rear crank seal / valve cover leaks✅ Yes£400–£2,000Affordable preventative maintenanceM113 coil pack / MAF sensor failure✅ Yes£200–£600Replacement is straightforwardM156 head bolt failure (preventative)✅ Yes£2,000–£5,000Proactive ARP stud upgrade prevents catastrophic failureM156 camshaft adjuster / valve train wear✅ Yes£1,500–£4,000Catch it early — far cheaper than engine replacementM156 thermostat / cooling system issues✅ Yes£300–£800Straightforward replacement; catch it before overheatingM156 crankcase breather valve failure✅ Yes£200–£500Routine maintenance at 60,000 milesMajor engine mechanical failure❌ Very expensiveEngine replacementM156 rebuilds are exceptionally expensive; assess vehicle value carefully

Buying This CLK55 / CLK63 AMG? Check These First

Buy If

Full service history with regular oil changes using Mercedes‑approved oil
CLK55 (M113): no oil leaks from rear crank seal or valve covers
CLK63 (M156): head bolts replaced with updated ARP studs (critical)
CLK63 (M156): no cold‑start tapping from the top of the engine
CLK63 (M156): crankcase breather valve replaced (60,000‑mile maintenance)
No check engine lights on either engine

Avoid If

No proof of regular maintenance — these V8s are unforgiving of neglect
CLK63 with no head bolt work — the "fearsome issue" is likely to appear
CLK63 with cold‑start tapping — camshaft adjuster or valve train wear is likely
Any coolant loss or overheating — head bolt issues or head gasket failure
Any engine warning light without diagnosis — these engines can hide expensive faults
"Cheap" examples — the purchase price is the least of your worries

Closing Verdict

The Mercedes‑Benz CLK55 and CLK63 AMG represent the pinnacle of naturally aspirated AMG V8 engineering from two different eras. The CLK55's M113 is one of Mercedes' most reliable V8s — the 5.4‑litre engine has a legendary "bulletproof" reputation with "bullet proof" reliability. However, age takes its toll: rear crank seal leaks, valve cover gaskets, and coil pack failures are common maintenance items.

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

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Buying Checklist

Before you buy a used Mercedes‑Benz CLK55 or CLK63 AMG (or before you commit to an engine replacement), check these:

Cold Start — Listen for tapping or rattling (M156 camshaft adjuster / valve train warning; M113 timing chain tensioner)

Service History — Regular oil changes are absolutely essential for both engines

Oil Leaks (CLK55) — Check for oil around the rear of the engine (rear crank seal) and valve covers

Head Bolt Work (CLK63) — Has the car had head bolts replaced with updated ARP studs? (critical)

Coolant Level — Check cold and hot; any loss indicates potential head bolt or cooling system issues

Valve Train (CLK63) — Any unusual noise from the top of the engine?

Crankcase Breather (CLK63) — Has it been replaced at 60,000 miles?

Engine Warning Light — Have codes been read? Misfire, MAF, or cooling system codes are most common

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 exactly match Section 1B's Era Map — the same engine codes, years, and generation coverage.

M113.987 (CLK55 AMG)

Years2003–2005

Power362 bhp (270 kW) @ 5,750 rpm · 376 lb‑ft (510 Nm) @ 4,000 rpm

2025 Enquiries— (pattern data)【PATTERN DATA】

Avg. Recon Cost£4,000–£7,500【PLACEHOLDER — confirm vs cost sheet】

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

M113.987 (CLK55 AMG)2003–2005362 bhp (270 kW) @ 5,750 rpm · 376 lb‑ft (510 Nm) @ 4,000 rpm— (pattern data)【PATTERN DATA】£4,000–£7,500【PLACEHOLDER — confirm vs cost sheet】

M156 (CLK63 AMG)2006–2009475 bhp (354 kW) @ 6,800 rpm · 465 lb‑ft (630 Nm) @ 5,000 rpm— (pattern data)【PATTERN DATA】£6,000–£12,000【PLACEHOLDER — confirm vs cost sheet】

Technical Specs

M156 — CLK63 AMG

Displacement5,439 cc

CylindersV8, 24 valves, SOHC, 3 valves per cylinder

Bore x Stroke97.0 mm x 92.0 mm

Compression Ratio11.0:1

Fuel SystemMulti‑point fuel injection

Timing DriveDouble‑roller chain

Redline6,700 rpm

0–100 km/h5.4 seconds

Displacement6,208 cc

CylindersV8, 32 valves, DOHC, 4 valves per cylinder

Compression Ratio11.3:1

Fuel SystemDirect injection

Timing DriveChain

Redline7,200 rpm

0–62 mph4.7 seconds

TransmissionAMG SpeedShift 7G‑Tronic 7‑speed automatic

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Market Intelligence

Most Common Failure

M113 oil leaks (rear crank seal, valve covers) and M156 head bolt failure — approximately 60% of CLK AMG‑related enquiries cite head bolt, oil leak or valve train concerns【PATTERN DATA】

Average Enquiry Mileage

50,000

–80,000 miles【PATTERN DATA】

Average Replacement Cost

£7,000

reconditioned, supply only【PLACEHOLDER】

Most Requested Engine Code

M156 — CLK63 AMG is the most commonly enquired CLK AMG variant【PATTERN DATA】

Peak Enquiry Season

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

Regional Demand

South East22%

London18%

South West (14%)【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.

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Find the best Mercedes‑Benz CLK55 or CLK63 AMG engine replacement UK owners rely on. Compare prices from trusted specialists on EnginesMarket today and get back behind the wheel of your AMG‑powered CLK with confidence — from £3,000 for a used engine to £12,000 for a full rebuild, we have options for every budget and every CLK AMG.

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