M276 vs M278 — Which Should You Buy?

The M276 wins for most buyers — it delivers 90% of the M278's performance with significantly lower running costs, better fuel economy and more predictable reliability. The M278 is a masterpiece of a V8, but its thirst and the risk of timing chain and camshaft adjuster issues make it an expensive proposition for everyday use.

M276 (3.0L V6 petrol): 390 enquiries in 2025 [EM-VERIFIED], typical reconditioned engine cost £3,800–£6,500 [EM-QUOTE], 255–362 bhp, known for timing chain stretch and carbon build-up
M278 (4.7L V8 petrol): 390 enquiries in 2025 [EM-VERIFIED], typical reconditioned engine cost £6,000–£10,000 [EM-QUOTE], 408–455 bhp, known for timing chain adjuster wear and turbocharger issues
M276 delivers significantly better fuel economy (32–35 mpg vs 24–28 mpg) and lower CO₂ emissions
M278's timing chain adjuster failure can be catastrophic; M276's chain stretch is less severe
M278 is used in larger, more prestigious models like the S‑Class and CLS; M276 is more widely fitted across the range

Full spec comparison, five‑year ownership cost analysis, and a clear verdict for your budget and driving needs below.

At a Glance

	M276 (3.0L V6)	M278 (4.7L V8)
2025 UK Enquiries	390 [EM-VERIFIED]	390 [EM-VERIFIED]
Displacement	3.0L V6 petrol	4.7L V8 petrol
Power Output	255–362 bhp	408–455 bhp
Recon Engine Supply & Fit	£3,800–£6,500	£6,000–£10,000
Typical Real‑World MPG	32–35	24–28
Defining Failure Points	Timing chain stretch, carbon build-up, water pump	Timing chain adjuster, camshaft adjuster, turbochargers
Best For	Balanced performance, efficiency, C/E/GLC/GLE models	V8 power, S‑Class/CLS/AMG‑lite, prestige

The Verdict

The M276 is the better engine for the vast majority of buyers. It offers strong performance, excellent refinement and much lower running costs than the M278. The M278 is an incredible V8 that delivers effortless power and a glorious sound, but its thirst and the risk of expensive timing chain adjuster failures make it a specialist choice. Unless you specifically want a V8 for its character and can afford the higher running costs, the M276 is the smarter, more practical choice.

M276 — The Refined V6

The M276 is Mercedes' 3.0‑litre V6 petrol engine, introduced in 2010 and used until 2021. It's a sophisticated, modern engine with direct injection, variable valve timing and excellent refinement. It was used across the range: C‑Class (W204/W205), E‑Class (W212/W213), GLC (X253), GLE (W166), CLS (C218), S‑Class (W222) and SL (R231). Power outputs range from 255 to 362 bhp depending on the variant — the 362 bhp version in the C43 AMG is a particularly sweet spot. The M276 is known for its smooth power delivery and surprisingly good fuel economy (32–35 mpg in real‑world driving). Key issues include timing chain stretch (especially on earlier models), carbon build‑up on intake valves, and water pump failure. These are generally less severe than the M278's timing chain adjuster problems. Replacement cost is £3,800–£6,500 [EM‑QUOTE], making it a relatively affordable engine to maintain. The M276 is the engine to choose if you want modern V6 performance without V8 running costs. See our M276 Knowledge Centre for full details.

M278 — The V8 Powerhouse

The M278 is Mercedes' 4.7‑litre V8 petrol engine, produced from 2010 to 2019. It's the twin‑turbo V8 that replaced the M273, delivering effortless power and a glorious soundtrack. It was used in the S‑Class (W221/W222 S500), CLS (C218 CLS500), E‑Class (W212 E500), GLE (W166 GLE500), GL (X166 GL500) and SL (R231 SL500). Power outputs range from 408 to 455 bhp, with peak torque arriving low in the rev range for effortless cruising. The M278 is a dream to drive, but it comes with significant running costs: 24–28 mpg in real‑world driving, higher VED, and expensive servicing. Known issues include timing chain adjuster wear (particularly on the right bank), camshaft adjuster failure, and turbocharger problems on higher‑mileage examples. These repairs can be very costly — timing chain adjuster work can run to £3,000–£5,000. Replacement cost for a reconditioned unit is £6,000–£10,000 [EM‑QUOTE]. The M278 is for those who want V8 prestige and performance and are prepared to pay for it. Our M278 Knowledge Centre has full specs and fitment details.

Cost & Ownership Comparison

The M276 is significantly cheaper to own than the M278 over a typical five‑year period. The difference is driven primarily by fuel — the M276's 32–35 mpg saves around £1,000–£1,500 per year compared to the M278's 24–28 mpg. Servicing costs are also lower on the V6, as it uses less oil and has fewer components. The M278's higher insurance premiums and VED add to the cost gap. Over 50,000 miles, the M276 typically costs its owner £5,000–£7,000 less to run than the M278, making it the more financially sensible choice for the vast majority of buyers. However, if you want the effortless V8 experience and can afford the extra costs, the M278 remains an exceptional engine.

Metric (5 yrs, 50k miles)	M276 (3.0L V6)	M278 (4.7L V8)
Fuel cost	£6,800–£7,400	£8,500–£9,800
Servicing (scheduled)	£1,000–£1,400	£1,500–£2,200
Tax (VED)	£800–£1,000	£1,200–£1,500
Insurance (estimated)	£2,800–£4,000	£3,500–£5,000
Total estimated	£11,400–£13,800	£14,700–£18,500

These figures are [ESTIMATED] based on UK market data and our proprietary enquiry patterns. Actual costs vary by driving style, location and individual vehicle condition.

Which Should You Buy?

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Best Value & Lowest Running Costs

M276 — significantly cheaper to run, cheaper to service, and still offers strong performance. The smart choice for most buyers.

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Maximum Performance & Prestige

M278 — effortless V8 power, a glorious soundtrack and the prestige of a V8. Only for those who can afford the running costs.

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Simpler Maintenance & Lower Risk

M276 — fewer catastrophic failure modes, cheaper parts and more widely understood by independent specialists. Lower probability of a major repair.

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V8 Sound & Character

M278 — the V8 rumble is unmatched. If the sound and feel of a V8 is what you're after, the M278 delivers in spades.

Whichever you choose, our repair vs replace calculator can help you decide what to do if you face a major engine failure.

Other Petrol Engine Comparisons

If you're still weighing up your options, these comparisons cover related Mercedes petrol engines.

M276 vs M278 →

You're here — V6 vs V8.

M272 vs M276 →

V6 generations compared.

M157 vs M178 →

AMG V8 comparison.

Diesel vs Petrol Running Costs →

Which fuel type suits your mileage?

For more detailed engine‑specific information, visit our M276 Knowledge Centre or M278 Knowledge Centre.

Frequently Asked Questions

Which is more reliable, M276 or M278?

The M276 is more reliable. The M278's timing chain adjuster failure can be catastrophic and expensive to fix. The M276's timing chain stretch is less severe and more predictable.

Which is cheaper to run, M276 or M278?

The M276 is significantly cheaper to run — it uses less fuel (32–35 mpg vs 24–28 mpg) and has lower servicing and insurance costs. The M278 is a thirsty V8.

Which sounds better, M276 or M278?

The M278 V8 has a glorious, deep rumble that the M276 V6 can't match. If sound is a priority, the M278 wins.

Can I fit an M278 into a car that originally had an M276?

No — the engine mounts, ECU, gearbox, cooling and exhaust systems are completely different. An engine swap between V6 and V8 platforms is not practical or cost‑effective.

Is the M276 powerful enough for a large car like the S‑Class?

Yes — the M276 in its higher‑output forms (362 bhp) provides more than adequate performance for the S‑Class and GLE. The M278 offers effortless extra power, but the M276 is perfectly capable.

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780 Combined EnquiriesM276 and M278 analysed from real 2025 UK data.

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A Real VerdictWe name a winner for most buyers, and explain when the M278 is worth the extra cost.

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15+ Vetted Mercedes SpecialistsExperienced with both petrol engines.

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100% IndependentNo sponsors, no manufacturer influence.