The Mercedes-Benz M273 is a naturally aspirated V8 gasoline engine produced from 2006 to 2012, representing the brand's mainstream eight-cylinder offering for the mid-to-late 2000s luxury lineup. Developed as a direct evolution of the well-regarded Mercedes-Benz M113, the M273 brought modern refinements including direct-acting DOHC valvetrain, Sentronic sequential gearbox compatibility, and improved thermal efficiency — all while retaining the smooth, effortless V8 character Mercedes buyers expected.
The M273 powers some of the most desirable S-Class, E-Class, CLS, and ML vehicles ever built, making it a popular choice in the used luxury market. It comes in two primary displacements — 4.7L and 5.5L — offering outputs between 302 hp and 388 hp, covering a broad range of applications from executive sedans to full-size SUVs.
For enthusiasts and buyers shopping the pre-owned luxury segment, understanding the M273's strengths, known failure points, and long-term ownership costs is essential. This guide covers everything you need to know.
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Base Specifications
| Spec | Detail |
|---|---|
| Type | Naturally aspirated V8 |
| Displacement | 4,663 cc (4.7L) / 5,461 cc (5.5L) |
| Block | Aluminum alloy |
| Head | Aluminum alloy, DOHC |
| Valvetrain | 32 valves, 4 valves per cylinder |
| Injection | Multi-point fuel injection (SFI) |
| Production Years | 2006–2012 |
M273 E46 — 302 hp / 339 lb-ft
The M273 E46 is the entry-level 4.7L variant, delivering a refined and smooth driving experience in executive and luxury SUV platforms. It uses a 4,663 cc displacement and is tuned for comfort-oriented performance.
| Model | Chassis | Years |
|---|---|---|
| E 500 | W/S 211 | 2006–2009 |
| CLS 500 | C 219 | 2006–2010 |
| ML 500 | W 164 | 2006–2011 |
| GL 500 | X 164 | 2006–2012 |
| R 500 | W 251 | 2006–2010 |
M273 E55 — 388 hp / 391 lb-ft
The M273 E55 is the larger 5.5L naturally aspirated variant, serving as the performance-oriented configuration across the flagship S-Class and related platforms. It replaced the supercharged M113 E55 AMG unit in standard (non-AMG) trim.
| Model | Chassis | Years |
|---|---|---|
| S 500 | W/V 221 | 2006–2013 |
| CL 500 | C 216 | 2006–2013 |
| E 500 | W/S 212 | 2009–2011 |
| ML 500 | W 164 | 2006–2011 |
| GL 500 | X 164 | 2006–2012 |
| R 500 | W 251 | 2006–2010 |
| SL 500 | R 230 | 2006–2011 |
How to Check a Used M273-Powered Car's History
Before buying any used car equipped with the M273, it is essential to ensure full transparency about its past. Undisclosed accidents and hidden mechanical abuse can directly compromise safety and reliability — particularly on high-value luxury vehicles where repair costs are disproportionately high relative to market value.
The M273 is frequently found in used S-Class, CLS, and ML models that have been previously tuned, subjected to deferred oil change intervals, or have had balance shaft and timing component wear left unaddressed. A vehicle showing no warning lights can still harbor significant internal wear or prior accident damage that was cosmetically repaired. Odometer fraud is also a documented concern on European-spec units imported to North America. It is strongly recommended to check the vehicle's complete history using its license plate or VIN number before any purchase decision.
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Key Strengths
The M273 earns genuine respect among Mercedes enthusiasts for several compelling reasons. First and foremost, its all-aluminum construction keeps weight in check while delivering strong thermal management — a notable improvement over older iron-block units. The engine's naturally aspirated character translates into linear, predictable power delivery that ages gracefully compared to force-inducted alternatives.
Refinement is exceptional: the M273 is noticeably smooth and quiet at idle and highway cruise, consistent with its flagship-class positioning. The 32-valve DOHC layout provides strong mid-range torque, making the engine feel effortless in everyday driving despite modest peak power figures on paper.
Aftermarket support is solid, with a wide range of OEM-equivalent replacement parts available for US buyers. The engine shares design DNA with the Mercedes-Benz M272 V6, meaning many independent specialists are familiar with its architecture. With proper maintenance, 200,000+ miles is achievable, and the engine rewards diligent ownership with long-term dependability.
Known Reliability Issues
Balance Shaft and Sprocket Wear
Symptom: Rattling noise from the front of the engine on cold start, timing-related fault codes, rough idle.
Cause: The balance shaft sprocket is made of a plastic-reinforced composite material that degrades over time, particularly under inconsistent oil change intervals. The sprocket teeth wear or shed, disrupting balance shaft timing.
Severity: Critical
Typical mileage: 80,000–130,000 miles
Note: This is the M273's most notorious failure point. The repair requires timing cover removal and replacement of the entire balance shaft assembly. Preventive replacement is strongly advised on any used M273 purchase above 80k miles. This issue is shared with the related Mercedes-Benz M272.
Camshaft Adjuster (VANOS-equivalent) Failure
Symptom: Rough idle, loss of low-end torque, P0010/P0020 camshaft position fault codes, increased fuel consumption.
Cause: The camshaft adjustment solenoids and associated actuators accumulate sludge deposits when oil is not changed frequently enough. The solenoid screens clog, starving the actuators of oil pressure and causing erratic variable valve timing behavior.
Severity: Moderate
Typical mileage: 70,000–120,000 miles
Note: Cleaning or replacing the camshaft solenoid screens is a relatively accessible first step. Full actuator replacement is required in advanced cases. Using 5W-40 fully synthetic oil and adhering to 10,000-mile or annual change intervals reduces risk significantly.
Oil Consumption and Valve Stem Seal Wear
Symptom: Blue smoke on startup or deceleration, oil level dropping between changes without visible leaks.
Cause: Valve stem seals harden with age and heat cycling, allowing oil to migrate past the stems into the combustion chamber. Higher-mileage units and those that have run consistently hot are most susceptible.
Severity: Moderate
Typical mileage: 100,000–160,000 miles
Note: Consumption of up to 1 quart per 1,000 miles is considered within Mercedes spec, but progressive worsening warrants seal replacement. The repair is labor-intensive but well within independent shop capability.
Coolant Leaks from Plastic Fittings and Reservoir
Symptom: Low coolant warning, visible coolant residue under the vehicle or on the engine bay floor, overheating in severe cases.
Cause: The M273 uses several plastic coolant fittings, expansion tank caps, and crossover pipes that become brittle over time due to thermal cycling. Cracks and micro-fractures develop gradually.
Severity: Moderate to Critical (if ignored)
Typical mileage: 80,000–150,000 miles
Note: Inspect all plastic coolant components during any major service. Proactive replacement of the coolant expansion tank and fittings is inexpensive insurance against a potential overheating event.
Rough Idle from Ignition Coils and Spark Plugs
Symptom: Misfires, engine stumble at idle, P030X misfire codes, slight hesitation under acceleration.
Cause: Ignition coils and iridium spark plugs wear gradually and are sensitive to oil contamination if valve cover gaskets are seeping. Coil-on-plug failures are common on higher-mileage units.
Severity: Minor to Moderate
Typical mileage: 60,000–100,000 miles
Note: A full coil and plug replacement as a set is the standard approach. OEM or OEM-equivalent coils are strongly preferred over budget aftermarket units, which tend to fail prematurely on the M273.
Maintenance Schedule
| Service | Interval |
|---|---|
| Engine oil and filter change | Every 10,000 miles or 12 months |
| Spark plug replacement | Every 60,000 miles |
| Air filter replacement | Every 30,000 miles |
| Coolant flush | Every 50,000 miles or 4 years |
| Transmission fluid change | Every 40,000 miles (severe) / 60,000 miles (normal) |
| Balance shaft inspection / replacement | At 80,000 miles or first purchase |
| Serpentine belt and tensioner | Every 80,000 miles |
| Valve cover gasket inspection | Every 60,000 miles |
| Camshaft solenoid screen cleaning | Every 40,000 miles |
Recommended oil specification: Mercedes-Benz 229.5 or 229.51 approved 5W-40 or 0W-40 fully synthetic — do not use conventional or low-grade synthetic oil. Extended drain intervals beyond 10,000 miles accelerate balance shaft and camshaft actuator wear.
Tuning Potential
The M273 is a naturally aspirated engine, which inherently limits dramatic power gains without significant hardware investment. That said, bolt-on modifications yield meaningful results on the larger 5.5L E55 variant, and the engine responds well to a well-rounded package.
| Stage | Modifications | Estimated Power |
|---|---|---|
| Stage 1 | ECU remap, high-flow air filter, sport exhaust | 310–330 hp (4.7L) / 405–420 hp (5.5L) |
| Stage 2 | Cold air intake, full exhaust system, camshaft upgrades | 340–360 hp (4.7L) / 430–450 hp (5.5L) |
| Stage 3 | Supercharger or turbo conversion, fueling upgrades, intercooler | 450–600+ hp (5.5L, forced induction) |
Recommended first modifications in order of priority:
- ECU remap — best return on investment for a naturally aspirated V8
- High-flow air filter or cold air intake — improves throttle response and top-end breathing
- Cat-back exhaust system — unlocks sound character and marginally improves flow
- Camshaft upgrade — meaningful gains for dedicated performance builds
- Forced induction conversion (supercharger preferred for M273 packaging) — for serious power targets
Fueling and cooling note: Beyond Stage 2, the stock fuel injectors and cooling system become limiting factors. A supercharger conversion requires upgraded fuel injectors, a larger fuel pump, and reinforced cooling capacity. The M273's aluminum block handles heat reasonably well, but sustained high-load use without cooling upgrades risks long-term head gasket stress.
FAQ
Is the Mercedes-Benz M273 a reliable engine?
The M273 is broadly reliable when properly maintained, but it carries well-documented weak points — most critically the balance shaft sprocket degradation. Buyers who address this proactively and follow strict oil change discipline can expect 150,000 to 200,000+ miles of dependable service. It is not a set-and-forget engine.
What is the most common problem with the M273?
The single most reported issue is balance shaft sprocket wear, which causes a distinctive cold-start rattle and can escalate to catastrophic timing failure if ignored. This is followed by camshaft adjuster solenoid clogging and plastic coolant fitting failure — all of which are manageable with preventive maintenance.
How long does the M273 engine last?
With regular fully synthetic oil changes, timely balance shaft service, and attention to cooling system components, the M273 routinely reaches 180,000 to 220,000 miles. High-mileage examples are common in the S-Class market and serve as proof of the engine's long-term potential when cared for.
How does the M273 compare to its predecessor, the M113?
The Mercedes-Benz M113 is widely regarded as slightly more robust in long-term durability due to its simpler valvetrain and fewer failure-prone plastic components. The M273 offers better refinement, improved efficiency, and a more modern architecture, but requires more attentive maintenance to avoid the balance shaft and camshaft actuator issues absent from the M113.
Can the M273 be tuned for serious performance?
The M273 responds modestly to bolt-on tuning as a naturally aspirated unit, but serious power requires forced induction — typically a supercharger conversion. The 5.5L E55 variant is the better platform for performance builds. For buyers who want substantial tuning potential from the factory, the AMG-built M156 or M157 are more appropriate choices.
Is the M273 suitable for daily driving when modified?
Yes — a Stage 1 tuned M273 remains fully daily-drivable with no meaningful compromise in refinement or reliability. The engine's smooth torque delivery and NVH refinement are preserved at Stage 1 levels. Beyond Stage 2, especially with forced induction, drivability trades begin to emerge, and long-term reliability becomes more dependent on build quality and supporting modifications.
Conclusion
The Mercedes-Benz M273 earns a reliability score of 7/10 and a tuning score of 5/10. It is a smooth, refined, and capable V8 that rewards attentive ownership — but demands respect for its known failure points, particularly the balance shaft sprocket and camshaft actuator systems. For buyers willing to invest in proper preventive maintenance, it remains one of the most satisfying naturally aspirated V8 platforms in the used luxury market. Browse our parts catalog to find everything you need to keep your M273 running at its best.