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Mercedes M278 Engine - Replacement Cost, Problems & CompatibilityProblems & Compatibility
The 4.6-litre and 5.5-litre twin-turbocharged V8 petrol engine fitted to flagship Mercedes-Benz models from 2011 to 2020, including the S-Class, E-Class, and GLS. Reconditioned Mercedes M278 units are typically available from £8,000 , reflecting the specialist nature of V8 biturbo replacement and consistent demand for this high-performance platform.
Supply & Fit Available
12-Month Warranty
Nationwide Delivery
100+ Suppliers
Used from
£4,000
Reconditioned from
£8,000
Rebuilt from
£12,000
GB
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Quotes only from vetted UK engine specialists.
Key Specs
Mercedes M278 - Specifications at a Glance
Engine Code
M278 (M278.920, M278.940, M278.950, M278.960)
Fuel
Petrol
Configuration
4.6L / 5.5L V8 twin-turbocharged (hot-vee layout)
Power Output(s)
300kW (408hp) - 395kW (537hp) depending on variant
Years Produced
2011-2020
UK Models Fitted
6+ Mercedes models - full list in Compatibility below
Replaced
M273 / M157
Replaced By
M177
Most Common Failure
Cylinder lining scuffing and timing chain stretch
Reconditioned Price Range
£8,000-£14,000 supply-only
Vetted UK specialists for M278 replacements
Minimum 12-month warranty on reconditioned and rebuilt options
Fitted To
Which Mercedes Models Use the M278-
TAG: Fitted To
| Model | Generation/Chassis | Badge(s) | Years | Link |
|---|---|---|---|---|
 Mercedes-Benz S-Class | W221 (Facelift) | S 500 | 2011-2013 | |
| Mercedes-Benz S-Class | W222 | S 500, S 550, S 560 | 2013-2020 | |
| Mercedes-Benz E-Class | W212 | E 500 | 2011-2016 | |
| Mercedes-Benz CLS | C218 | CLS 500 | 2011-2018 | |
| Mercedes-Benz ML / GLE | W164 / W166 | ML 550, GLE 450, GLE 500 | 2011-2019 | |
| Mercedes-Benz GL / GLS | X166 / X167 | GL 450, GL 550, GLS 450, GLS 500 | 2012-2020 |
02
Mercedes-Benz S-Class
03
Mercedes-Benz E-Class
04
Mercedes-Benz CLS
05
Mercedes-Benz ML / GLE
Generation/Chassis
W164 / W166
Badge(s)
ML 550, GLE 450, GLE 500
Years
2011-2019
06
Mercedes-Benz GL / GLS
CROSS-BRAND
M278 is documented across 6 BMW applications spanning S-Class, E-Class, CLS, ML / GLE, GL / GLS. Registration lookup confirms the exact suffix before quotes are sent.
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Prices
Mercedes M278 Engine Replacement Cost (UK)
Condition | Supply Only | Fitted (Independent Specialist) | Typical Warranty |
|---|---|---|---|
Used | £4,000-£8,000 | £5,040-£9,430 | 3-6 months |
Reconditioned | £8,000-£14,000 | £9,040-£15,430 | 12-24 months |
Rebuilt | £12,000-£18,000 | £13,040-£19,430 | 12-24 months |
The final cost of a Mercedes M278 engine replacement is heavily influenced by whether the unit requires cylinder bore sleeving to address lining scuffing, and the condition of the twin turbochargers. If turbo failure has caused internal oil contamination or if the cylinder walls are severely scored, a standard reconditioned swap may not suffice, pushing the requirement toward a fully rebuilt unit with upgraded thermal management components. See our full reconditioned engine cost guide for a detailed breakdown of what is included at each price tier.
Labour Guide
Fitting a Mercedes M278 typically takes 16-22 hours at £65/hr (independent specialist rate) - confirm exact labour when comparing quotes, as the hot-vee turbo layout and extensive ancillary disassembly significantly increase labour time.
Price Factors
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Common Problems
Mercedes M278 Engine Problems - What Actually Fails
Every engine has its weak points. Here are the known issues with the M278, based on real-world data and verified failure patterns.
Verified issue focus: Cylinder lining scuffing and timing chain stretch.
1. Cylinder Lining Scuffing (Nikasil Coating Wear)
1. Cylinder Lining Scuffing (Nikasil Coating Wear)
Typical onset:
50,000-100,000 miles
What happens:
Early production M278 engines (particularly the initial 4.6L M278.920 and some early 5.5L units) are susceptible to cylinder wall scoring and Nikasil coating degradation. This manifests as excessive oil consumption, blue smoke from the exhaust, misfires, and a progressive loss of compression. If ignored, the scoring worsens, leading to catastrophic bottom-end damage from oil starvation.
Repair vs replace:
If caught early, the block can sometimes be sleeved or line-bored, but the labour intensity and risk of underlying damage often make a full Mercedes M278 engine replacement the more reliable long-term solution.
Read more about this issue
2. Timing Chain Stretch and Guide Wear
2. Timing Chain Stretch and Guide Wear
Typical onset:
60,000-120,000 miles
What happens:
Sharing the hot-vee V8 architecture with the M273 and M157, the M278 is prone to timing chain stretch and plastic guide wear over time. This manifests as a distinct metallic rattling noise on cold starts, followed by check engine lights indicating camshaft correlation faults. If ignored, the chain can jump teeth, leading to catastrophic valve-to-piston contact.
Repair vs replace:
If caught early, replacing the timing chain kit, tensioners, and guides is viable, though it is a highly labour-intensive job requiring significant front-end strip-down. If internal damage has already occurred, a full Mercedes M278 engine replacement is the only reliable solution.
Read more about this issue
3. Turbocharger Wastegate Rattle and Valley Pan Oil Leaks
3. Turbocharger Wastegate Rattle and Valley Pan Oil Leaks
Typical onset:
70,000-120,000 miles
What happens:
The hot-vee layout places the twin turbochargers directly in the valley between the cylinder banks, subjecting them to extreme heat. This accelerates wastegate actuator wear and linkage rattle, leading to boost pressure faults. Additionally, the heat cycles cause the valley pan seals and oil cooler O-rings to harden and crack, resulting in persistent oil leaks and a burning oil smell in the cabin.
Repair vs replace:
Wastegate actuators and valley pan seals can be replaced as preventative maintenance. However, if turbo bearing wear has led to oil ingestion and internal engine scoring, a full rebuild is necessary to prevent repeat failure.
Read more about this issue
Compare rebuilt M278 prices with the failure already addressed
Engine Variants
How to Confirm You Have the Mercedes M278
The M278 engine code is stamped directly onto a machined pad on the engine block, typically located near the oil filter housing or the bell housing. It is also clearly listed on your vehicle's V5C registration document under "Engine Number" and can be decoded from the full VIN. Common Confusion Warning: Owners frequently confuse the M278 with other Mercedes V8 engines: - M157: The AMG-specific 5.5L biturbo V8. While mechanically similar, the M157 features AMG-specific engine mounts, ECU calibration, and exhaust routing, making it incompatible as a direct swap for a standard M278. - M177: The newer 4.0L AMG biturbo V8. It features a completely different block architecture, hot-vee turbo sizing, and engine management system. - M273: The older 5.5L naturally aspirated V8. It lacks the twin-turbo setup entirely, meaning the intake, exhaust, and ECU architectures are completely incompatible. Fitting the wrong revision will result in severe ECU, wiring loom, and exhaust manifold incompatibilities.
Not 100% sure- Enter your registration above - we'll confirm your exact M278 fitment before any quotes are sent.
Easily Confused
M273
- The naturally aspirated 4.5L-5.5L V8 it replaced, which lacked twin turbochargers and featured a different intake and exhaust architecture, avoiding the M278's hot-vee thermal vulnerabilities.
Alternative / Next-Gen Code
M157
- The early AMG-specific 5.5L biturbo V8 that shared similar architecture but featured AMG-specific mounts, ECU calibration, and exhaust routing, making it incompatible as a direct swap for a standard M278.
Related JLR Variants
M177
- The direct 4.0L twin-turbo V8 successor introduced from 2015, featuring a more compact hot-vee layout, direct injection, and revised thermal management, largely resolving the M278's cylinder lining and timing chain vulnerabilities.
Confirm the exact M278 fitment
Not 100% sure- Enter your registration above - we'll confirm your exact M278 fitment before any quotes are sent.
Buying Guide
Buying a Replacement Mercedes M278 - What to Choose
Choosing the right replacement route depends on your budget, risk tolerance, and ownership goals. Here's a breakdown of your options.
Used:
A used Mercedes M278 is only advisable for lower-mileage host vehicles and *only* if accompanied by documented, stamped service history proving rigorous oil changes (every 5,000-8,000 miles) and no prior complaints of excessive oil consumption or cold-start rattles. The risk of inheriting cylinder lining scuffing or timing chain stretch is unacceptably high without this proof.
Reconditioned:
This is the most recommended route for the M278. A proper reconditioned unit will include verified cylinder bore integrity (or sleeved bores if applicable), brand-new timing chain components, refreshed valley pan seals, and tested twin turbochargers, directly addressing the V8's known weak points out of the box.
Rebuilt:
A full rebuild is justified if your original M278 suffered catastrophic cylinder scoring that damaged the pistons, or if severe turbo failure caused oil starvation to the crankshaft bearings. A specialist rebuild will machine the block, fit upgraded thermal management components, and ensure all oil galleries are clear.
Supply & Fit Line:
Sourcing a replacement is only half the job. Our network provides full supply and fit services, ensuring the engine is installed by Mercedes and V8-specialist technicians with a nationwide warranty backing both the labour and the unit.
Vehicle Value Note:
For flagship hosts like the W222 S-Class, W212 E-Class, and X166 GL/GLE, current UK market values typically sit between £8,000 and £35,000 . With a reconditioned M278 replacement costing from £8,000 (plus £1,040-£1,430 fitting), the repair cost generally represents 20-40% of the vehicle's value, making replacement financially viable for well-maintained examples. However, for early W212 E500 or W164 ML550 hosts valued under £6,000, we strongly advise evaluating the car's scrap or part-exchange value before committing to a V8 engine replacement.
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Related Engines
Engines Related to the Mercedes M278
Explore engines that are closely related to the Mercedes-Benz M278, including its predecessor, successor, and key family variants.
Predecessor
M273
- The naturally aspirated 4.5L-5.5L V8 it replaced, which lacked twin turbochargers and featured a different intake and exhaust architecture, avoiding the M278's hot-vee thermal vulnerabilities.
Predecessor
M157
- The early AMG-specific 5.5L biturbo V8 that shared similar architecture but featured AMG-specific mounts, ECU calibration, and exhaust routing, making it incompatible as a direct swap for a standard M278.
Successor
M177
- The direct 4.0L twin-turbo V8 successor introduced from 2015, featuring a more compact hot-vee layout, direct injection, and revised thermal management, largely resolving the M278's cylinder lining and timing chain vulnerabilities.
FAQ
Mercedes M278Frequently Asked Questions
Question 1How much does a Mercedes M278 engine replacement cost in the UK-
A Mercedes M278 engine replacement typically costs between £8,000 and £14,000 for a reconditioned supply-only unit . Fitted costs generally add £1,040-£1,430 for independent specialist labour due to V8 biturbo complexity, and fully rebuilt units with upgraded thermal management components can reach £12,000-£18,000 supply-only.
- Fitted costs generally add £1,040-£1,430 for independent specialist labour due to V8 biturbo complexity.
- Fully rebuilt units with upgraded thermal management components can reach £12,000-£18,000 supply-only.
Question 2What is the most common failure with the Mercedes M278 engine-
The most documented failure patterns for the M278 are cylinder lining scuffing (Nikasil coating wear) and timing chain stretch. Early warning signs include excessive oil consumption, blue smoke, misfires, or a metallic rattle on cold starts, and if ignored, cylinder scoring worsens or the chain jumps teeth, leading to catastrophic valve-to-piston contact requiring full engine replacement.
- Early warning signs include excessive oil consumption, blue smoke, misfires, or a metallic rattle on cold starts.
- If ignored, cylinder scoring worsens or the chain jumps teeth, leading to catastrophic valve-to-piston contact requiring full engine replacement.
Question 3Which Mercedes models use the M278 engine-
The M278 is fitted to Mercedes-Benz flagship models from 2011 to 2020, including the S-Class (W221, W222), E-Class (W212), CLS (C218), and the large SUV platforms (ML/GLE/GL/GLS). It powers badges ranging from the E500 and CLS500 to the S500, S550, and GL550, and you should always verify your exact fitment via registration lookup before ordering parts.
- It powers badges ranging from the E500 and CLS500 to the S500, S550, and GL550.
- You should always verify your exact fitment via registration lookup before ordering parts.
Question 4Should I buy a used or reconditioned Mercedes M278 engine-
A reconditioned Mercedes M278 is strongly recommended over a used unit due to the well-documented cylinder lining scuffing and timing chain failure risks. Used units carry a high probability of inheriting the same latent wear unless accompanied by stamped proof of preventative maintenance and no oil consumption complaints, whereas a proper reconditioned M278 includes verified cylinder bore integrity, new timing chain components, refreshed valley pan seals, and tested twin turbochargers as standard.
- Used units carry a high probability of inheriting the same latent wear unless accompanied by stamped proof of preventative maintenance and no oil consumption complaints.
- A proper reconditioned M278 includes verified cylinder bore integrity, new timing chain components, refreshed valley pan seals, and tested twin turbochargers as standard.
Question 5What is the difference between the M278 and the M157 or M177-
The M278 is the standard flagship 4.6L/5.5L twin-turbo V8, while the M157 is the AMG-specific variant with different mounts, ECU calibration, and exhaust routing. The M177 is the newer 4.0L twin-turbo V8 successor, featuring a completely different block architecture, hot-vee turbo sizing, and engine management system, meaning fitting an M157 or M177 as a direct replacement for an M278 will result in severe mounting, wiring loom, and exhaust manifold incompatibilities.
- The M177 is the newer 4.0L twin-turbo V8 successor, featuring a completely different block architecture, hot-vee turbo sizing, and engine management system.
- Fitting an M157 or M177 as a direct replacement for an M278 will result in severe mounting, wiring loom, and exhaust manifold incompatibilities.
Compare Mercedes M278 Engine Prices Today
Get a free, no-obligation comparison for your exact Mercedes M278 engine code and sub-code. Our registration lookup confirms your precise fitment before any quotes are sent, ensuring you receive accurate pricing for your specific vehicle. With reconditioned M278 units starting from an estimated £8,000, comparing specialist quotes takes just two minutes and could save you thousands on your replacement.
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Vetted UK specialists for M278 replacements
Minimum 12-Month Warranty
Minimum 12-month warranty on reconditioned and rebuilt options
Nationwide Delivery
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