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 Kompressor single-row chain, the M272 balance shaft, the M273 idler gear, and the early OM651 piezoelectric injectors all share the same era. The OM612 and M113 score 85+/100. If you're looking at a Mercedes built between 2003 and 2010, the engine code matters more than the mileage.
M271 Kompressor — 35/100 (AVOID)
1.8L Kompressor I4
Found in: C 180 Kompressor, C 200 Kompressor, C-Class, CLK, CLK 200 Kompressor, E-Class, SLK
Known problems
| Issue | Severity | Typical cost | Onset |
|---|---|---|---|
| Single-row timing chain stretch — catastrophic | critical | €4.000 | 60.000 km |
| Balance-shaft plastic sprocket wear (pre-2010) | high | N/A | N/A |
| Supercharger clutch / belt failure | high | €1.500 | 80.000 km |
| Part-load crankcase breather hoses crack | minor | N/A | N/A |
| Camshaft sensor magnets leak oil into wiring harness and ECU | moderate | €800 | N/A |
Full M271 Kompressor reliability report →
M271 EVO (CGI turbo) — 58/100 (CAUTION)
1.8L CGI Turbo I4
Found in: C 250, C-Class, E-Class, SLK
Known problems
| Issue | Severity | Typical cost | Onset |
|---|---|---|---|
| Camshaft adjuster and tensioner wear — timing drift, chain can jump | critical | €4.000 | 50.000 km |
| Camshaft sensor magnets leak oil into wiring harness and ECU | moderate | €800 | N/A |
| Intake-valve carbon build-up (direct injection) | moderate | €700 | 80.000 km |
Full M271 EVO (CGI turbo) reliability report →
M278 — 59/100 (CAUTION)
M278 4.7 V8 Biturbo
Found in: S-Class, SL
Known problems
| Issue | Severity | Typical cost | Onset |
|---|---|---|---|
| Bore scoring and piston scuffing - oil consumption, engine failure | critical | N/A | N/A |
| Exhaust valve guide and seat wear - misfire, cylinder head repair (warranty extension) | high | €9.200 | N/A |
| Oil wicking from cam adjusters and sensors into the wiring harness and ECU | high | €10.100 | N/A |
| Timing chain tensioners and check valves (early engines) - cold-start rattle, chain wear | high | N/A | N/A |
| Catalytic converter sulphur contamination (warranty extension) | moderate | N/A | N/A |
Full M278 reliability report →
M156 — 61/100 (CAUTION)
M156 6.2 V8 AMG
Found in: C-Class, CLK, E-Class
Known problems
| Issue | Severity | Typical cost | Onset |
|---|---|---|---|
| Cylinder head bolt failure (engines up to serial 60-060658) | critical | €9.200 | 129.000 km |
| Intake camshaft and hydraulic lifter wear | high | N/A | 113.000 km |
| Camshaft adjuster and sprocket wear - cold-start rattle | moderate | €4.600 | 97.000 km |
| Intake manifold centre plate / runner wear | moderate | €5.520 | N/A |
| Rising oil consumption | moderate | N/A | 97.000 km |
Full M156 reliability report →
M272 — 65/100 (CAUTION)
V6 NA 2.5-3.5L
Found in: C 280, C-Class, CLK, CLK 350, E-Class, ML 350, S 350, S-Class
Known problems
| Issue | Severity | Typical cost | Onset |
|---|---|---|---|
| Balance-shaft sprocket wear (early engines, US settlement) | critical | €3.600 | 60.000 km |
| Camshaft adjuster magnet oil leak (oil wicking into the harness) | minor | N/A | N/A |
| Map-controlled thermostat failure | minor | N/A | N/A |
| Spark plugs + ignition coils | minor | €600 | 80.000 km |
| High-pressure fuel pump failure (CGI direct injection only) | moderate | N/A | N/A |
Full M272 reliability report →
OM642 — 65/100 (CAUTION)
3.0L V6 Diesel
Found in: C-Class, CLK, E 350d, E-Class, G-Class, GLC, GLE, GLE 350d
Known problems
| Issue | Severity | Typical cost | Onset |
|---|---|---|---|
| Crankshaft main bearing failure (mainly up to MY 2009) | critical | N/A | 150.000 km |
| Swirl flap / intake port shut-off (EKAS) failure | high | €2.800 | N/A |
| Valley oil cooler seal failure | high | €2.000 | N/A |
| BlueTEC NOx / emissions software recall | moderate | €1.500 | 60.000 km |
| EGR valve and cooler sooting | moderate | N/A | N/A |
Full OM642 reliability report →
What to buy instead
Not all Mercedes-Benz engines are problematic. These score well:
- OM612 — 92/100 (BEST)
- M264 — 89/100 (BEST)
- M113 — 89/100 (BEST)
- M256 — 88/100 (BEST)
Generated from EngineScope's reliability database. Reviewed by the editorial team. Methodology →