Mercedes/M156
Mercedes · Naturally aspirated

Mercedes C63 AMG M156

C63 AMG·W204·2007–2014·6,208 cc·Verified 13 Jul 2026

"After doing a lot of research I have found a lot of issues with the M156 motor. Some say the issues are in very low numbers, but search deep enough and you find plenty of expensive stories."

RISKY
45/ 100
"Glorious V8, but budget for rebuilds"
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Power Variants

451 hp · 600 Nm
M156
2007-2011
Original C63 AMG launch tune, the most common variant on the used market
457 hp · 600 Nm
M156
2011-2014
Facelift ECU remap gave a small power bump with no internal hardware changes
480 hp · 600 Nm
M156
2011-2014
AMG Performance Package option, revised ECU map and uprated engine mounts, top speed raised to 250 km/h, same base internals as standard cars
517 hp · 590 Nm
M156 (Black Series specification)
2012-2013
C63 AMG Black Series, dry sump lubrication and forged internals for higher load tolerance, but wider track and stiffer suspension mean these cars are more often track driven, which shortens practical service life

Recommendation

Do not choose a C63 purely by advertised hp figure. The 451, 457, and 480 hp cars share the same wet-sump engine and the same head bolt and camshaft adjuster risks, so service history matters far more than the power tune. The 517 hp Black Series has genuinely different internals (dry sump, forged pistons and rods) which reduces some bearing wear risk, but these cars are frequently used harder and cost significantly more to source parts for, so the reliability advantage can be offset by harder use and higher repair bills when something does go wrong. For a daily-driven buy, a well documented standard or Performance Package car with proof of head bolt and camshaft adjuster attention is the safer bet over an undocumented Black Series.

622
Max HP
650
Torque Nm
8,000
Oil interval km
0
Recalls
7
Known issues

Known Issues

Head Bolt Failure€3,000-8,000 · 80,000-160,000 kmCRITICAL

The M156 has a well-documented head bolt failure issue discussed extensively across Mercedes forums. Bolts can stretch and lose clamping force, leading to head gasket failure and potential coolant/oil contamination. Forum debate exists over how widespread the failure rate truly is, but the cost of repair when it occurs is severe.

Coolant loss with no visible external leak
White smoke from exhaust
Overheating
Milky oil on dipstick
DIY: Expert only
Camshaft Adjuster / Inlet Camshaft Adjuster Failure€800-2,500 · 60,000-130,000 kmHIGH

Inlet camshaft adjusters are a known weak point on the M156. Forum reports describe a characteristic cold-start rattle traced to worn or failed camshaft adjusters rather than timing chain tensioners. Full replacement of adjusters and associated components is required.

Cold-start rattle that may diminish once warm
Rough idle
Check engine light related to camshaft timing
DIY: Hard
Rod and Main Bearing Wear€2,000-6,000 · 100,000-200,000 kmHIGH

Bearing clearance and wear is a monitored concern in M156 engines at higher mileages. Forum threads discuss measuring crankshaft journal clearances and the risk of finding worn bearings upon engine inspection. Color-coded main and rod bearings require careful sourcing during rebuild.

Deep knocking noise under load
Low oil pressure warning
Metallic debris in oil
DIY: Expert only
Fuel Injector Failure€1,500-4,000 · 80,000-150,000 kmHIGH

A forum rebuild thread documents an M156 engine requiring full rebuild triggered by a bad fuel injector causing internal damage. Injector failure can have downstream consequences beyond the injector itself if not caught early.

Rough running or misfires
Fuel smell in oil
Uneven idle
Check engine misfire codes
DIY: Moderate
Valve Lifter / Tappet Wear€1,000-3,000 · 80,000-160,000 kmMODERATE

Valve lifters and tappets are recommended for replacement during major engine work on the M156. Forum rebuild accounts specifically list SLS Black Series tappets as preferred replacements, indicating the OEM units are prone to wear.

Ticking noise from valve train
Increased valve noise at idle
Reduced high-RPM performance
DIY: Hard
Water Pump Failure€400-900 · 80,000-140,000 kmMODERATE

Water pump replacement is listed as a standard item during major M156 engine work, suggesting premature or expected wear. Given the engine's high thermal load as a naturally aspirated high-revving V8, cooling system integrity is critical.

Coolant leak from front of engine
Overheating
Coolant warning light
DIY: Moderate
722.9 Gearbox Shift Quality / TCU Tune€300-1,500 · 0-300,000 kmLOW

The 722.9 7-speed automatic paired with the M156 is reported by owners as having slower shift responses compared to DCT alternatives. TCU tuning options exist to improve shift speed. Not a mechanical failure risk but a known ownership irritation noted in forums.

Sluggish gear changes
Hesitant downshifts under hard acceleration
DIY: Easy (TCU tune only)
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Buying Checklist

Demand full documented service history with oil change intervals no greater than 8,000 km, skipped oil services accelerate camshaft adjuster and bearing wear
Perform a cold-start test and listen carefully for any rattle in the first 30 seconds, camshaft adjuster noise is a red flag requiring immediate investigation
Request evidence that head bolts have been inspected or replaced; if unknown, budget for this as a priority post-purchase job
Check for coolant contamination in oil (milky dipstick or cap residue) and oil contamination in coolant expansion tank, both indicate potential head bolt or head gasket failure
Inspect oil for metallic debris and ask for any recent oil analysis results, bearing wear produces particles detectable before audible knock develops
Test drive the car hard through the full RPM range and check for misfires, rough running, or hesitation that could indicate injector issues or cam timing faults
If considering a Black Series, confirm dry-sump oil system service history separately, its lubrication and internals differ from the standard C63 engine

Service Reality

Community oil interval8,000 km
Oil specificationMercedes-Benz Sheet 229.5, 0W-40 or 5W-40 full synthetic
Est. ownership cost (2yr)€9,000-18,000 over 3 years including fuel, tyres, routine maintenance, and provisioning for known high-cost repairs such as head bolts and camshaft adjusters
Real mix fuel consumption14.2 L/100km

Strong Points

✓First engine designed entirely in-house by AMG, built to racing-derived principles
✓Naturally aspirated 6.2L V8 produces a legendary exhaust note and linear power delivery
✓High-revving character with power extending to over 7,000 rpm
✓When properly maintained and rebuilt, the engine is known to last to high mileages
✓Strong aftermarket and specialist support with rebuild parts readily available
✓No turbo or supercharger complexity, fewer forced induction failure points

Also Found In

Mercedes-Benz E63 AMG (W211/W212)Mercedes-Benz S63 AMG (W221)Mercedes-Benz SL63 AMG (R230)Mercedes-Benz CLK63 AMG (A209)Mercedes-Benz ML63 AMG (W164)Mercedes-Benz GL63 AMG (X164)Mercedes-Benz G63 AMG (W463)Mercedes-Benz SLS AMG (C197, related M159 derivative)

Time Bomb Parts Inspect Proactively

Head bolts
Inspect and replace proactively; verify no prior failure history before purchase
80,000 km
Inlet camshaft adjusters
Replace at first sign of cold-start rattle; do not ignore
60,000 km
Valve lifters / tappets
Replace during any top-end work; use upgraded SLS Black Series spec
100,000 km
Water pump
Replace preventatively during any major service or engine work
90,000 km
Fuel injectors
Test balance and condition; replace any suspect units before internal damage occurs
100,000 km

Tuning Risk If This Example Has Been Modified

MODERATE
Signs of modification
•ECU tune; a specific and well-documented quirk of this exact model is that Mercedes electronically restricted the C63's throttle bodies from opening fully (a factory 'detune' relative to more expensive M156-equipped models like the E63 or CLS63), meaning a tune on a C63 specifically often unlocks unusually large gains, commonly cited as 100-120+whp when combined with headers, by simply allowing the throttle bodies to open as far as they do on other M156 applications
•Long-tube headers (either catted/high-flow-catted or, for competition-only use, catless), a common and effective modification given the engine's naturally aspirated design
•Aftermarket throttle bodies (a modest gain, typically 10-13hp, more effective paired with a tune and headers)
•Catback exhaust, mainly for sound rather than meaningful power
•Supercharger kit on a small minority of heavily built examples; a comparatively rare, expensive, and complex undertaking rather than a simple bolt-on
Can this be hidden before a sale?

An ECU tune on this platform can generally be reverted to a stock-reading file. Headers, throttle bodies, and exhaust hardware are physical bolt-ons and are directly checkable by inspection, though a seller could revert these to stock parts before a sale.

Physical checks that still work, even after a reflash
•Aftermarket headers, throttle bodies, or exhaust still physically present despite a stock-reading ECU
•A catless header/exhaust setup, which is illegal for street use and checkable via a straightforward underside inspection
•Supercharger hardware, unmistakable if fitted
•A cold-start rattle from the top of the engine: this is not a tuning-related symptom but is specifically flagged by owners as one of the most important checks on any example of this engine, tuned or not, since it can indicate camshaft lobe or valve lifter/tappet wear, a well-documented factory issue independent of modification status
•Recently replaced cam lobes, lifters/tappets, cam adjuster plates, or head bolts with no matching service record, which can indicate a prior major repair for this engine's known baseline issues
Weak points if pushed
Engine block and bottom end
Specialist sources are consistent that this is a strength rather than a weakness: the closed-deck block, silicon-aluminum construction, and factory piston design are described as capable of handling 750-800hp with the stock bottom end, well beyond what any street-based tuning or supercharger build would typically approach, meaning the practical mechanical ceiling for tuning risk on this engine is unusually high
Valve train (lifters, cam lobes, cam adjuster plates, head bolts)
This is this engine's well-documented Achilles' heel, but based on available sources it appears to be a baseline design/manufacturing issue present on stock and tuned examples alike (pre-~2011 production is specifically affected by a head bolt corrosion issue that Mercedes later fixed), rather than something clearly worsened by mild tuning; still, given how serious and expensive a failure can be, this is arguably the single most important thing to check on any example of this engine, tuned or not
Not clearly tuning-related; a serious baseline reliability consideration on any example of this engine
Supporting mods and risk

This is a case where the tuning-specific risk picture is genuinely reassuring: the bottom end is massively over-engineered relative to what naturally aspirated bolt-on tuning can extract from it, and much of the C63's unusually large tuning response comes from a documented factory throttle-body restriction being lifted, effectively bringing the car in line with tuning states Mercedes already used elsewhere in the M156 range, rather than pushing the engine into genuinely new territory. The far more consequential risk for any buyer of this engine is unrelated to tuning status: pre-2011-production head bolts, camshaft lobes, and valve lifters/tappets are subject to well-documented factory design issues that can result in expensive engine-out repairs, and this risk exists whether or not the car has ever been modified. A car with a full history of preventative valve train and head bolt work (with receipts) is a meaningfully safer buy than an unmodified but undocumented example, and modification status alone is not a reliable proxy for this engine's real risk.

Emissions delete risk

Catless long-tube headers are a real, discussed option on this engine, but specialist sources are explicit that catless exhaust setups are illegal for street use and should be reserved for competition-only builds; catted or high-flow-catted long-tube headers are the street-legal alternative. A catless setup will fail an MOT/roadworthiness emissions inspection in the UK/EU and equivalent tests elsewhere.

This profile reflects consensus from MBWorld.org, MBClub UK, BenzWorld.org, and specialist technical write-ups (FCP Euro, 8020 Automotive, MBH Motorsports), not manufacturer-confirmed limits. The valve train and head bolt issues are widely discussed and MBWorld/MBClub forum members describe genuinely divided opinions on their real-world prevalence, ranging from 'blown out of proportion' to 'inevitable grenade,' so treat individual claims with some caution and prioritize documented service history over forum sentiment. Treat any example of this engine, tuned or not, as needing a careful cold-start listen for valve train noise, a check of head bolt replacement history (pre- vs. post-fix production), and injector condition as part of a full pre-purchase inspection, rather than relying on an OBD scan alone.

Buying Advice

The M156 is one of the greatest naturally aspirated V8s ever built, but it demands respect and budget. Buy only a car with full documented service history and evidence of short oil change intervals, neglect accelerates every known failure mode. Budget a minimum of €2,000-4,000 for preventative work regardless of the car's apparent condition, covering camshaft adjusters, water pump, and head bolt inspection. This is an enthusiast's engine that rewards careful ownership but will punish those who treat it like a normal road car.

Community Sentiment

Mixed to cautious. Enthusiasts love the engine's character and sound, but forum consensus acknowledges real and expensive failure modes, particularly head bolts and camshaft adjusters. Owners who maintain them properly report high-mileage survival; neglected examples generate the horror stories. The internet amplifies failures, but the costs when things go wrong are genuinely high.

Frequently Asked Questions

// 18 logged
❯How reliable is the Mercedes C63 AMG M156?

The Mercedes C63 AMG M156 has a reliability score of 45/100, rated "RISKY". Glorious V8, but budget for rebuilds

❯What are the common problems with the M156?

The most frequently reported issues are Head Bolt Failure, Camshaft Adjuster / Inlet Camshaft Adjuster Failure, Rod and Main Bearing Wear, Fuel Injector Failure, among others. See the Known Issues section above for symptoms, affected mileage, and repair costs.

❯Does the M156 have head bolt failure problems?

Yes, this is a documented issue on the M156, typically appearing around 80,000-160,000 km. The M156 has a well-documented head bolt failure issue discussed extensively across Mercedes forums. Bolts can stretch and lose clamping force, leading to head gasket failure and potential coolant/oil contamination. Forum debate exists over how widespread the failure rate truly is, but the cost of repair when it occurs is severe. Typical repair cost: €3,000-8,000. DIY difficulty: Expert only.

❯Does the M156 have camshaft adjuster / inlet camshaft adjuster failure problems?

Yes, this is a documented issue on the M156, typically appearing around 60,000-130,000 km. Inlet camshaft adjusters are a known weak point on the M156. Forum reports describe a characteristic cold-start rattle traced to worn or failed camshaft adjusters rather than timing chain tensioners. Full replacement of adjusters and associated components is required. Typical repair cost: €800-2,500. DIY difficulty: Hard.

❯Does the M156 have rod and main bearing wear problems?

Yes, this is a documented issue on the M156, typically appearing around 100,000-200,000 km. Bearing clearance and wear is a monitored concern in M156 engines at higher mileages. Forum threads discuss measuring crankshaft journal clearances and the risk of finding worn bearings upon engine inspection. Color-coded main and rod bearings require careful sourcing during rebuild. Typical repair cost: €2,000-6,000. DIY difficulty: Expert only.

❯Does the M156 have fuel injector failure problems?

Yes, this is a documented issue on the M156, typically appearing around 80,000-150,000 km. A forum rebuild thread documents an M156 engine requiring full rebuild triggered by a bad fuel injector causing internal damage. Injector failure can have downstream consequences beyond the injector itself if not caught early. Typical repair cost: €1,500-4,000. DIY difficulty: Moderate.

❯Does the M156 have valve lifter / tappet wear problems?

Yes, this is a documented issue on the M156, typically appearing around 80,000-160,000 km. Valve lifters and tappets are recommended for replacement during major engine work on the M156. Forum rebuild accounts specifically list SLS Black Series tappets as preferred replacements, indicating the OEM units are prone to wear. Typical repair cost: €1,000-3,000. DIY difficulty: Hard.

❯Does the M156 have water pump failure problems?

Yes, this is a documented issue on the M156, typically appearing around 80,000-140,000 km. Water pump replacement is listed as a standard item during major M156 engine work, suggesting premature or expected wear. Given the engine's high thermal load as a naturally aspirated high-revving V8, cooling system integrity is critical. Typical repair cost: €400-900. DIY difficulty: Moderate.

❯Is the M156 worth buying used?

The M156 is one of the greatest naturally aspirated V8s ever built, but it demands respect and budget. Buy only a car with full documented service history and evidence of short oil change intervals, neglect accelerates every known failure mode. Budget a minimum of €2,000-4,000 for preventative work regardless of the car's apparent condition, covering camshaft adjusters, water pump, and head bolt inspection. This is an enthusiast's engine that rewards careful ownership but will punish those who treat it like a normal road car.

❯Should I buy a Mercedes C63 AMG with the M156 engine?

Do not choose a C63 purely by advertised hp figure. The 451, 457, and 480 hp cars share the same wet-sump engine and the same head bolt and camshaft adjuster risks, so service history matters far more than the power tune. The 517 hp Black Series has genuinely different internals (dry sump, forged pistons and rods) which reduces some bearing wear risk, but these cars are frequently used harder and cost significantly more to source parts for, so the reliability advantage can be offset by harder use and higher repair bills when something does go wrong. For a daily-driven buy, a well documented standard or Performance Package car with proof of head bolt and camshaft adjuster attention is the safer bet over an undocumented Black Series.

❯What should I check before buying a used M156?

Before buying, check: Demand full documented service history with oil change intervals no greater than 8,000 km, skipped oil services accelerate camshaft adjuster and bearing wear; Perform a cold-start test and listen carefully for any rattle in the first 30 seconds, camshaft adjuster noise is a red flag requiring immediate investigation; Request evidence that head bolts have been inspected or replaced; if unknown, budget for this as a priority post-purchase job; Check for coolant contamination in oil (milky dipstick or cap residue) and oil contamination in coolant expansion tank, both indicate potential head bolt or head gasket failure; Inspect oil for metallic debris and ask for any recent oil analysis results, bearing wear produces particles detectable before audible knock develops.

❯How many km will a M156 last?

There's no fixed mileage limit, it depends on maintenance. The parts worth budgeting for proactively are: Head bolts (80,000 km), Inlet camshaft adjusters (60,000 km), Valve lifters / tappets (100,000 km), Water pump (90,000 km). Engines that clear these checkpoints with documented maintenance commonly continue well beyond typical ownership periods.

❯How much does it cost to maintain a M156?

Estimated ownership cost is €9,000-18,000 over 3 years including fuel, tyres, routine maintenance, and provisioning for known high-cost repairs such as head bolts and camshaft adjusters, based on known issues and typical service needs.

❯What is the real-world fuel consumption of the M156?

Owners report real-world fuel consumption of around 14.2 L/100km, compared to the official figure of 6.6 L/100km.

❯What oil should I use in a M156, and how often?

Community-reported real-world usage suggests changing oil every 8,000 km using Mercedes-Benz Sheet 229.5, 0W-40 or 5W-40 full synthetic, often more conservative than the official service schedule.

❯Is it safe to tune or remap the M156?

The M156 is commonly modified, with a moderate risk level when pushed beyond stock. Typical weak points under tuning: Engine block and bottom end, Valve train (lifters, cam lobes, cam adjuster plates, head bolts). Emissions-delete modification is a known risk area on this engine.

❯What other cars use the M156 engine?

The M156 is also found in: Mercedes-Benz E63 AMG (W211/W212), Mercedes-Benz S63 AMG (W221), Mercedes-Benz SL63 AMG (R230), Mercedes-Benz CLK63 AMG (A209), Mercedes-Benz ML63 AMG (W164), Mercedes-Benz GL63 AMG (X164), Mercedes-Benz G63 AMG (W463), Mercedes-Benz SLS AMG (C197, related M159 derivative).

❯Why does the M156 have a bad reputation?

Glorious V8, but budget for rebuilds The biggest recurring complaint is Head Bolt Failure. Mixed to cautious. Enthusiasts love the engine's character and sound, but forum consensus acknowledges real and expensive failure modes, particularly head bolts and camshaft adjusters. Owners who maintain them properly report high-mileage survival; neglected examples generate the horror stories. The internet amplifies failures, but the costs when things go wrong are genuinely high.

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