What these engines share
The hot-V twin-turbo V8 showdown: BMW's N63 (2008–present, 550i, 750i, X5 50i) vs Mercedes' M278 (2010–2019, E500, S500, GLE 500). Both use a 'hot-V' layout with turbos between the cylinder banks for shorter intake paths.
N63 vs M278 at a glance
| N63 | M278 | |
|---|---|---|
| Brand | BMW | Mercedes-Benz |
| Score | 42/100 | 62/100 |
| Verdict | AVOID | CAUTION |
| Type | N63 4.4 V8 Twin-Turbo | M278 4.7 V8 Biturbo |
| Known issues | 2 | 2 |
N63 — 42/100 (AVOID)
Found in: 5 Series, 6 Series, 7 Series, 8 Series, X5
Key issues
- Injector failure (hot-V design) — severity critical, cost €5.000, onset 60.000 km
- Excessive oil consumption — severity high, cost €2.000, onset 40.000 km
M278 — 62/100 (CAUTION)
Found in: S-Class, SL
Key issues
- Timing chain guide failure — severity critical, cost €8.000, onset 80.000 km
- Turbo oil line leak — severity high, cost €1.500, onset 60.000 km
Verdict: M278 wins by 20 points
The M278 scores 62/100 vs the N63's 42/100 — a 20-point difference. This is a significant gap. The M278 is clearly the safer choice.
Which one should you buy?
Neither is a low-cost ownership proposition. The N63 has a longer and more troubled reliability history — the 'customer care' programme for early N63s was effectively an extended warranty for known issues. The M278 is more reliable but significantly more expensive to repair when things go wrong. For a used V8, set aside a serious maintenance budget regardless of badge.
Generated from EngineScope's reliability database. Reviewed by the editorial team. Methodology →