Why some Mercedes-Benz engines score below 68/100
Mercedes-Benz earned its reliability reputation in the W124 era — and spent two decades gradually eroding it. The worst offenders cluster in the 2003–2010 generation, where cost-cutting met complexity. Knowing which engines to avoid is the difference between a bargain and a money pit.
The pattern
The Mercedes avoid list is overwhelmingly a 2003–2010 problem: the M271 single-row chain, the M272 balance shaft, the M273 idler gear, and the early OM651 piezoelectric injectors all share the same era. The OM606, M112/M113, and modern OM654 score 85+/100. If you're looking at a Mercedes built between 2003 and 2010, the engine code matters more than the mileage.
M271 — 35/100 (AVOID)
1.8L SC I4
Found in: C 180, C 180 Kompressor, C 200, C 200 Kompressor, C 250, C-Class, CLK, CLK 200 Kompressor
Known problems
| Issue | Severity | Typical cost | Onset |
|---|---|---|---|
| Single-row timing chain stretch — catastrophic | critical | €3.500 | 60.000 km |
| Supercharger clutch / belt failure | high | €1.500 | 80.000 km |
| Valve cover gasket oil leak | moderate | €500 | 80.000 km |
Full M271 reliability report →
OM651 (early) — 38/100 (AVOID)
2.1L Diesel I4
Found in: A-Class, B-Class, C 200d, C 220d, C-Class, CLA, CLK, E-Class
Known problems
| Issue | Severity | Typical cost | Onset |
|---|---|---|---|
| Timing chain stretch (pre-2014) | critical | €2.500 | 80.000 km |
| Piezoelectric injector failure (pre-2014) | critical | €3.500 | 60.000 km |
| DPF + EGR fouling (city use) | high | €1.200 | 60.000 km |
Full OM651 (early) reliability report →
M273 — 45/100 (AVOID)
V8 NA 4.7-5.5L
Found in: S 500, S-Class
Known problems
| Issue | Severity | Typical cost | Onset |
|---|---|---|---|
| Idler gear sprocket wear — same class-action as M272 | critical | €4.500 | 60.000 km |
| Spark plugs + ignition coils (8 of each) | minor | €900 | 80.000 km |
Full M273 reliability report →
M272 — 50/100 (CAUTION)
V6 NA 2.5-3.5L
Found in: C 280, C 350, C-Class, CLK, CLK 350, E-Class, ML 350, S 350
Known problems
| Issue | Severity | Typical cost | Onset |
|---|---|---|---|
| Balance shaft sprocket wear — class-action | critical | €4.000 | 60.000 km |
| Spark plugs + ignition coils | minor | €600 | 80.000 km |
| Intake manifold swirl flaps failure | moderate | €900 | 80.000 km |
Full M272 reliability report →
M279 — 55/100 (CAUTION)
M279 6.0 V12 Biturbo
Found in: S-Class
Known problems
| Issue | Severity | Typical cost | Onset |
|---|---|---|---|
| Turbo failure | critical | €10.000 | 60.000 km |
| ABC suspension fluid contamination | high | €5.000 | 40.000 km |
Full M279 reliability report →
M166 — 55/100 (CAUTION)
M166 A-Class 1.4/1.6
Found in: A-Class
Known problems
| Issue | Severity | Typical cost | Onset |
|---|---|---|---|
| Head gasket failure | high | €1.200 | 60.000 km |
Full M166 reliability report →
What to buy instead
Not all Mercedes-Benz engines are problematic. These score well:
- OM606 — 96/100 (BEST)
- M112/M113 — 92/100 (BEST)
- OM648 — 90/100 (BEST)
- M104 — 85/100 (BEST)
Generated from EngineScope's reliability database. Reviewed by the editorial team. Methodology →