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Mercedes M278 4.7 L Twin‑Turbo V8 (2010–2020): Overview, Common Issues & Maintenance
The M278 Engine is Mercedes-Benz’s twin-turbocharged 4.7 L V8 petrol engine, designed to replace the natural-aspirated M273. Debuting around 2010, it features direct injection, twin-scroll turbos, and advanced timing chain architecture, offering improved performance, efficiency, and emissions reductions.
It’s widely used across the Mercedes lineup, including models like the S-Class, E-Class, CLS 257, and GL-Class, offering a refined yet powerful driving experience.
M278 engine is known for its smooth power delivery and strong torque across the rev range, but like any complex powertrain, it comes with its share of common issues.
In this article, we’ll break down its technical specs, known reliability concerns, and the most frequent problems reported by owners such as timing chain wear and oil leaks. We’ll also cover the models it powers and offer practical maintenance tips to help keep your M278 engine performing at its best for years to come.
Technical Specifications of the M278 Engine
| Variant | Displacement | Power | Torque | Applications |
|---|---|---|---|---|
| Standard M278 | 4.663 L V8 | 300 kW (S‑Class, CLS, E‑Class etc.) | 600 Nm | E500, CLS500, ML500, GL500, SL550 etc. |
| M278 tuned (high output) | Same | 320 kW (S550, W222 etc.) | 700 Nm | S550/SL550 post-2014 |
Key specs: V8, DOHC, VVT, twin-scroll turbos, direct injection, timing-chain-driven cams. Shared architecture with M273 but advanced in injection and boost systems.
- – Engine Type: V8, twin-turbocharged
- – Power Output:
- – E500 / E550: 402 hp and 600 Nm (443 lb-ft) of torque
- – GL500 / S500: 429 hp and 700 Nm (516 lb-ft) of torque
- – Fuel System: Direct fuel injection
- – Compression Ratio: 10.5:1
- – Max RPM: 6,000
- – Turbocharging: Two turbochargers, one per cylinder bank
- – Transmission: Typically paired with 7G-Tronic or 9G-Tronic automatic transmissions.
The twin-turbo design ensures the engine delivers strong torque across a wide RPM range, resulting in impressive acceleration and effortless highway cruising.
M278 engine problems & Fixes
While the M278 engine is an advanced and reliable engine, some common issues can arise as mileage increases. Below are the most frequently reported problems and how to address them.
1. Oil Leaks from Timing Chain Covers
- – Symptoms: Oil spots under the engine or an oil smell in the cabin.
- – Cause: Weak seals on the timing chain covers, leading to leaks.
- – Solution: Reseal the covers and replace worn gaskets. Regular inspections can prevent severe leaks.
2. Turbocharger Issues
- – Symptoms: Power loss, whistling sounds from the engine, and black smoke from the exhaust.
- – Cause: Wastegate failure or carbon buildup in the intake.
- – Solution: Clean the intake system and replace or rebuild the turbocharger if necessary.
3. Timing Chain Stretch
- – Symptoms: Rattling noises on cold starts, check engine light with codes P0016/P0017.
- – Cause: The timing chain stretches over time, and the tensioners wear out.
- – Solution: Replace the chain, guides, and tensioners to avoid further engine damage.
4. High Oil Consumption
- – Symptoms: Frequent need to top up engine oil between services.
- – Cause: Worn valve stem seals lead to oil leaking into the combustion chamber.
- – Solution: Replace valve stem seals to prevent oil consumption issues.
5. Carbon Buildup in Intake Valves
- – Symptoms: Rough idling, misfires, and reduced performance.
- – Cause: Direct injection engines, like the M278, can develop carbon deposits on intake valves.
- – Solution: Perform walnut blasting or chemical cleaning every 60,000 km to remove carbon buildup.
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| Issue | Symptoms | Diagnosis & Fix |
|---|---|---|
| Timing chain tensioner rattle | Rattle at cold start | Inspect primary & secondary chains/tensioners after ~150k km; replace if worn |
| Intake valve carbon buildup | Rough idle, misfires, low performance | Perform walnut blasting every ~60k km |
| Turbocharger/turbine wear | Whistle noise, boost loss | Check actuator/turbo; replace if worn |
| Low-compression due to bore scoring | Loss of power, misfire | Test cylinder compression/leak-down; diagnose scoring issues |
| Oil leaks (valve cover/gaskets) | Oil puddles, burning smell | Replace gaskets early; inspect coolant hoses and wiring |
M278 reliability
The M278 engine is regarded as a reliable V8 engine with proper maintenance. With many examples surpassing 200,000 km, it is clear that this engine can perform well over the long term if owners stay on top of preventive care.
Strengths:
- – Powerful twin-turbo V8 with smooth performance.
- – Improved fuel efficiency compared to older V8 engines.
- – Reduced emissions to comply with stricter environmental regulations.
Weaknesses:
- – Turbochargers can develop issues over time.
- – Timing chain stretch can occur with high mileage.
- – Intake valve carbon buildup requires periodic cleaning.
Overall, the M278 provides a great balance of performance and efficiency but demands attention to maintenance to stay in peak condition.
Models Equipped with the M278 Engine
The M278 engine powers some of Mercedes-Benz’s most luxurious and powerful models, enhancing their performance while maintaining comfort. Here are some of the key models equipped with this engine:
CL-Class: CL500, CL550
SL-Class: SL500, SL550
These models benefit from the M278’s combination of power, smoothness, and efficiency, making them ideal for luxury driving experiences.
M273 vs m278 : Key Differences
| Feature | M273 Engine | M278 Engine |
|---|---|---|
| Induction | Naturally Aspirated | Twin-Turbocharged |
| Power Output | Up to 382 hp | Up to 429 hp |
| Fuel Delivery | Port Injection | Direct Injection |
| Fuel Economy | Lower efficiency | Higher efficiency |
| Emissions Compliance | Lower compliance | Meets stricter regulations |
| Performance | Smooth but less powerful | More torque and acceleration |
The M278 engine outshines the M273 in nearly every category, offering better power and efficiency through the use of twin-turbocharging and direct injection.
Maintenance Tips for the M278 Engine
Proper maintenance is essential to keep the M278 engine running smoothly. Here are some important tips for owners:
- 1. Oil Changes: Use fully synthetic oil (5W-40) and change it every 8,000 – 10,000 km.
- 2. Turbocharger Inspection: Check for leaks and listen for unusual sounds to detect turbo issues early.
- 3. Timing Chain Inspection: Inspect the chain after 150,000 km and replace it if needed.
- 4. Carbon Cleaning: Perform intake valve cleaning every 60,000 km to prevent misfires and rough idling.
- 5. Cooling System Check: Monitor for leaks around the water pump and radiator to avoid overheating.
Keeping up with these maintenance tasks will help avoid expensive repairs and prolong the life of the engine.
Conclusion
The Mercedes M278 engine offers a powerful, modern solution for those who appreciate the performance of a V8 without sacrificing efficiency. Thanks to twin-turbocharging and direct injection, the M278 delivers impressive torque and acceleration across a range of luxury vehicles.
While the engine has some known issues such as oil consumption, carbon buildup, and timing chain wear proactive maintenance can prevent these problems from becoming major repairs. With proper care, the M278 can provide years of reliable service and continue to impress with its performance and refinement.
For enthusiasts who want the perfect blend of power, luxury, and efficiency, the M278 V8 is a fantastic choice.
Frequently Asked Questions
Is the M278 reliable?
Yes, if maintained on schedule. Timing chain tensioners and carbon buildup are common, but manageable issues.
When should intake valves be cleaned?
Every ~60,000 km, especially since it’s direct-injection; walnut blasting is recommended.
What causes compression loss?
Score marks in cylinder bores common around cyl 1 & 5. Do compression and leak-down tests to diagnose.
How long do turbos last?
Generally durable, but inspect for wear and actuator function. Oil maintenance is crucial.
