What to Know About the Mercedes-Benz M273 Engine

The Mercedes-Benz M273 engine is a naturally aspirated V6 and V8 powerplant produced from 2004 to 2017, widely used across the brand’s luxury lineup including the E-Class, S-Class, CLS, and GLK. Known for its smooth operation and strong low-end torque, the M273 replaced the earlier M112 and M113 engines with improved efficiency, variable valve timing (VVT), and aluminum construction. However, like many modern Mercedes engines, it comes with specific failure points that owners should understand before buying or maintaining a vehicle equipped with this unit. This comprehensive guide covers everything you need to know about the M273 engine—its design, common issues such as oil leaks, balance shaft failures, and intake manifold actuator wear, long-term reliability, maintenance best practices, and what to consider when looking at a used or replacement M273 engine ⚙️.

Understanding the M273 Engine: Design and Applications

The M273 engine family was introduced by Mercedes-Benz in 2004 as part of a broader shift toward lightweight, fuel-efficient, yet powerful engines. It succeeded the older M112 (V6) and M113 (V8) series and featured several technological upgrades, including dual overhead camshafts (DOHC), four valves per cylinder, and advanced variable valve timing on both intake and exhaust camshafts—a system Mercedes called Variable Nockenwellen Steuerung (VANOS) in some markets, though technically distinct from BMW’s system of the same name.

Available in both 3.5L V6 and 5.5L V8 configurations, the M273 powered numerous high-volume Mercedes models between 2005 and 2017. Key applications include:

• W211 E350 / E500 (2005–2009)
• W221 S350 / S550 (2006–2013)
• R230 SL350 / SL500 (2006–2011)
• W204 C350 / C500 (2008–2014)
• W164 ML350 / ML500 (2006–2011)
• C219 CLS350 / CLS500 (2005–2010)
• R171 SLK350 (2008–2011)

Unlike turbocharged successors like the M276 and M176, the M273 is entirely naturally aspirated, relying on displacement and precise valvetrain control for performance. The engine block is made of aluminum alloy, reducing overall weight while maintaining rigidity. It uses electronic throttle control, coil-on-plug ignition, and Bosch ME 9.7 engine management systems for optimized fuel delivery and emissions compliance 🔧.

Performance Specifications by Displacement

The M273 came in two primary displacements, each tuned differently depending on application and market:

Engine Variant	Displacement	Horsepower (HP)	Torque (lb-ft)	Years Produced	Notable Models
M273 E35	3.5L V6	268–272	258–260	2005–2017	E350, S350, ML350
M273 E55	5.5L V8	382–402	391–398	2005–2014	S500, CLS500, SL500

The 5.5L V8 version delivers robust acceleration without forced induction, making it one of the last naturally aspirated large-displacement engines offered by Mercedes before the industry-wide shift to downsizing and turbocharging. Despite not being classified as a high-performance AMG unit, the M273 V8 provides a refined driving experience with minimal vibration and linear power delivery—hallmarks of Mercedes-Benz engineering during that era ✨.

Common M273 Engine Problems and Failure Points

While generally reliable compared to later turbocharged units, the M273 has several known weak points that can lead to expensive repairs if ignored. Understanding these issues helps buyers assess risk and owners plan preventative maintenance.

1. Oil Leaks from Valve Cover Gaskets and Front Crankshaft Seal

One of the most frequent complaints with the M273 is oil seepage, particularly from the valve cover gaskets. Over time, the rubber seals degrade due to heat cycling and age, leading to visible oil stains around the top of the engine. While not immediately dangerous, persistent leaks can contaminate spark plugs, trigger misfires, and create smoke under the hood when oil drips onto hot exhaust manifolds.

The front crankshaft seal is another common leak point, especially on higher-mileage vehicles. A failing seal will leave oil streaks along the passenger side of the engine and may drip onto the serpentine belt, causing slippage or noise. Replacing these seals requires significant labor, so they are often addressed during major services 1.

2. Intake Manifold Runner Adjuster (IMRA) Actuator Wear

The M273 uses variable-length intake runners controlled by electric actuators mounted on the intake manifold. These actuators adjust airflow based on RPM to optimize torque across the rev range. However, the plastic gears inside the actuators are prone to cracking or stripping after 80,000–120,000 miles.

Symptoms include:

• Check Engine Light (P2004, P2005, P2006 codes)
• Rough idle or hesitation at low speeds
• Reduced fuel economy

Replacement actuators are available from OEM and aftermarket suppliers. Some owners opt for upgraded metal-gear versions to prevent recurrence 🔍.

3. Balance Shaft Assembly Issues (Especially in Early Models)

Unlike the inline-six M272 engine, which had documented balance shaft failures, the V6 M273 does not use a traditional balance shaft system. However, some confusion arises because the M273 shares design elements with the M272. The V8 variant inherently balances well due to its 90-degree V configuration.

That said, early M273 engines (pre-2008) had an intermediate shaft drive system that could develop play or noise if maintenance was delayed. This is more accurately described as a timing chain tensioner or guide wear issue rather than a balance shaft problem. Regular oil changes using correct viscosity (229.5-certified 0W-40 or 5W-40) help extend the life of these components.

4. Coolant Leaks from Water Pump and Thermostat Housing

The electric water pump used in the M273 is integrated into the coolant circuit near the thermostat housing. After 100,000 miles, the seals can fail, leading to coolant loss and potential overheating. Unlike mechanical pumps, the electric version runs continuously based on ECU input, increasing wear over time.

A failing thermostat or housing gasket can also cause similar symptoms. Because the entire assembly is often replaced as a unit, labor costs can be high. Proactive replacement around 100k–120k miles is recommended for longevity 🧰.

5. Spark Plugs and Ignition Coils Degradation

Spark plugs in the M273 are typically rated for 60,000-mile service intervals. Beyond that, electrode erosion increases the risk of misfires, rough running, and catalytic converter damage. Ignition coils, while generally durable, can fail individually, often mimicking fuel-related issues.

When servicing, it’s advisable to replace all six or eight spark plugs (depending on configuration) and inspect coils for carbon tracking or cracking. Using only OEM-specification or high-quality aftermarket plugs ensures consistent combustion.

M273 vs. M272: Key Differences Buyers Should Know

There is frequent confusion between the M273 and the smaller M272 engine, both of which were used in overlapping model years and chassis. Here’s how they differ:

Feature	M273	M272
Configuration	V6/V8	V6 only
Displacement	3.5L or 5.5L	2.5L, 3.0L, 3.5L
Naturally Aspirated	Yes	Yes
Balance Shaft	No (V8 balanced; V6 uses counterweights)	Yes (known failure point)
Typical Use Case	Luxury sedans, SUVs, coupes	Entry-level luxury (C-Class, E-Class)
Reliability	Generally good with proper maintenance	More problematic due to balance shaft and oil consumption

If you're shopping for a used Mercedes with a 3.5L engine, confirming whether it's an M272 or M273 is critical. The M273-powered models tend to offer better refinement and durability, especially in heavier vehicles where the extra torque matters 📊.

Is the M273 Engine Reliable Long-Term?

With proper care, the M273 engine can reliably reach 150,000 to 200,000 miles. Its naturally aspirated design avoids the complexity and heat stress associated with turbocharging, contributing to longer component life. However, reliability hinges heavily on maintenance history.

Key factors affecting longevity:

• Oil Change Frequency: Every 5,000–7,500 miles with MB-approved full synthetic oil (e.g., Mobil 1 Turbo or Liqui Moly Top Tec 4600).
• Cooling System Service: Replace coolant every 4 years or 60,000 miles to protect the water pump and heater core.
• Intake System Inspection: Clean carbon buildup from intake valves every 80,000 miles, especially on direct-injected variants.
• Timing Chain Health: Monitor for rattling noises on cold start, which may indicate stretched chains or failed tensioners.

Engines with neglected oil changes or coolant flushes are far more likely to suffer premature wear. Always request service records when purchasing a used vehicle with an M273 engine 📋.

Buying a Used M273 Engine: What to Look For

Whether replacing a damaged engine or restoring a classic Mercedes, sourcing a used M273 requires careful evaluation. Many are sold online via eBay, Alibaba, and specialty auto recyclers. Here’s what to verify before purchase:

1. Mileage and Maintenance History

Ask for documented proof of regular oil changes and major services. Engines with under 100,000 miles and complete records are preferable. Be cautious of “low-mileage” claims without verification.

2. Leak Inspection

Request clear photos of the valve covers, oil pan, and rear main seal area. Any sign of active oil leakage suggests degraded gaskets that may require immediate attention post-installation.

3. Compression and Leak-Down Test Results

A reputable seller should provide recent compression and leak-down test data. Healthy M273 cylinders typically show 180–210 psi with less than 10% variation between banks. Values below 160 psi indicate potential internal wear.

4. Presence of Known Fault Codes

Scan the engine’s ECU for stored codes related to VANOS, IMRA, or misfires. Even if the engine runs, unresolved issues can resurface after installation.

5. Warranty and Return Policy

Some suppliers offer 6-month warranties on tested engines. Avoid sellers who refuse returns or provide vague descriptions. Platforms like eBay Motors allow buyer protection, but international shipments (e.g., from Alibaba) may lack recourse 🛒.

Rebuilt vs. Remanufactured M273 Engines

When the original engine fails beyond repair, options include:

• Used Engine: Lower cost ($800–$2,000), but unknown lifespan.
• Rebuilt Engine: Core engine disassembled, worn parts replaced, then reassembled. Often includes new pistons, rings, bearings. Cost: $3,000–$5,000.
• Remanufactured Engine: Fully restored to factory specs using CNC machining and quality control. Typically comes with warranty. Cost: $5,000–$8,000.

For long-term ownership, a remanufactured unit from a certified supplier offers the best value despite higher upfront cost. Companies like Reman Engine and Adsitco specialize in Mercedes powerplants and perform rigorous testing before shipment 🏭.

Maintenance Schedule for M273 Engine Longevity

To maximize engine life and avoid costly repairs, follow this recommended maintenance timeline:

Mileage	Service Task	Notes
0–10,000	Oil & filter change	Use MB 229.5 spec oil
60,000	Replace spark plugs	All cylinders, inspect coils
80,000	Inspect IMRA actuators	Replace if noisy or faulty
100,000	Coolant flush, water pump inspection	Consider proactive replacement
120,000	Valve cover gasket replacement	Prevent future leaks
150,000+	Compression test	Assess internal health

Sticking to this schedule minimizes unexpected breakdowns and preserves resale value ✅.

Frequently Asked Questions (FAQs)

❓ Is the Mercedes M273 engine interference or non-interference?

The M273 is an interference engine. If the timing chain breaks or jumps, piston-to-valve contact is likely, resulting in severe internal damage. Regular inspection of tensioners and guides is essential.

❓ How much does it cost to replace an M273 engine?

Labor ranges from $1,500 to $3,000 depending on the model. Combined with a used engine ($1,000–$2,500) or remanufactured unit ($5,000+), total costs can reach $8,000. DIY swaps reduce labor expenses significantly.

❓ Can I upgrade the M273 engine with forced induction?

While possible, adding turbochargers or superchargers requires extensive modifications to fuel delivery, cooling, ECU tuning, and internal components. Most owners prefer keeping the engine stock due to complexity and cost.

❓ Are there any recalls related to the M273 engine?

There are no widespread safety recalls specific to the M273 engine. However, certain model years had technical service bulletins (TSBs) regarding IMRA actuators and water pump failures. Check with a dealer using your VIN.

❓ What years did Mercedes use the M273 engine?

The M273 was used from model year 2005 through 2017, with the V8 discontinued earlier (2014) and the V6 continuing in select markets until 2017.