The Mercedes-Benz OM651 engine marked a significant step forward in diesel technology for the German automaker. Introduced in October 2008, this inline-four cylinder diesel engine was designed as a replacement for the successful OM646 and OM642 series, aiming to deliver improved efficiency, power, and reduced emissions. Production of the OM651 motor was based in Stuttgart, Germany, underscoring its importance as a core Mercedes-Benz engine.
The OM651 is part of a broader lineage of Mercedes-Benz diesel R4 engines, which includes iconic series such as the OM616, OM601, OM604, OM611, OM640, OM646, OM654, and OM668. This engine family showcases Mercedes-Benz’s long-standing commitment to diesel innovation and performance.
In its debut year, the OM651 brought a wave of advancements to Mercedes-Benz’s 4-cylinder diesel offerings. It features a robust cast-iron cylinder block paired with a lightweight aluminum 16-valve cylinder head. The engine incorporates hydraulic lifters and a sophisticated combined timing drive utilizing a roller chain, gears, and balancer shafts for smooth and reliable operation. Turbocharging is a key aspect of the OM651, with simpler versions employing an IHI VV20 or VV21 variable geometry turbine, while higher-output variants boast a BorgWarner R2S bi-turbo system for enhanced performance.
Early high-performance versions of the OM651 were equipped with a Delphi fuel system using piezo injectors. However, these injectors proved problematic, leading to issues. Mercedes-Benz transitioned to electromagnetic injectors starting in 2010 and initiated a recall in 2011 to replace the piezo injectors in previously produced engines. Basic versions of the engine consistently used a Bosch fuel system with electromagnetic injectors, known for their reliability.
The Mercedes OM651 motor is available in two main displacement versions: the 1796 cc DE18 LA and the 2143 cc DE22 LA. Despite the common 2143 cc displacement, power outputs vary significantly, ranging from 107 hp to 204 hp. Models producing over 170 hp (125 kW) utilize the twin-turbo system, while those below 100 kW feature a single turbocharger setup.
Mercedes-Benz OM651 Engine Specifications
| Feature | Specification |
|---|---|
| Production Years | Since 2008 |
| Displacement, cc | 1796 (DE 18 LA red), 1796 (DE 18 LA), 2143 (DE 22 LA red), 2143 (DE 22 LA) |
| Fuel System | Common Rail |
| Power Output, hp | 109 (DE 18 LA red), 136 (DE 18 LA), 95 – 143 (DE 22 LA red), 163 – 204 (DE 22 LA) |
| Torque Output, Nm | 250 (DE 18 LA red), 300 (DE 18 LA), 250 – 360 (DE 22 LA red), 350 – 500 (DE 22 LA) |
| Cylinder Block | Cast Iron R4 |
| Block Head | Aluminum 16v |
| Cylinder Bore, mm | 83 |
| Piston Stroke, mm | 83 (DE 18 LA red), 83 (DE 18 LA), 99 (DE 22 LA red), 99 (DE 22 LA) |
| Compression Ratio | 16.2 |
| Hydraulic Lifters | Yes |
| Timing Drive | Chain & Gears |
| Recommended Engine Oil | 5W-30 |
| Engine Oil Capacity, Liter | 6.5 (11.5 in commercial models) |
| Fuel Type | Diesel |
| Euro Standards | EURO 5/6 |
| Fuel Consumption, L/100 km (Mercedes E 250 CDI 2015) | City: 6.9, Highway: 4.4, Combined: 5.3 |
| Engine Lifespan, km | ~400,000 |
| Weight, kg | 203.8 |
This detailed specification table provides a comprehensive overview of the technical aspects of the Mercedes OM651 engine, highlighting the variations in displacement, power, and torque across different models. The use of Common Rail fuel injection and adherence to EURO 5/6 emission standards underscore its modern design.
Key Features of the Mercedes OM651 Motor
The OM651 engine incorporates several advanced features that contribute to its performance, efficiency, and compact design.
One notable feature is its compact and low-profile design, achieved through the rear camshaft drive. This design element was crucial for meeting pedestrian protection regulations, demonstrating Mercedes-Benz’s commitment to safety and regulatory compliance.
The engine utilizes a 4th generation common rail direct injection system. Initially, piezo injectors were used, but due to reliability concerns, Mercedes-Benz transitioned to conventional electromagnetic injectors. This system provides injection pressures up to 2000 bar, allowing for precise fuel delivery. Direct control of the injector needle enables highly flexible injection timing and smoother engine operation. This results in a balance of high performance, excellent fuel economy, and reduced exhaust emissions.
The combustion chamber design and lower compression pressure are optimized to minimize raw exhaust gas emissions, particularly nitrogen oxides (NOx). A maximum cycle pressure of up to 200 bar further enhances engine performance and contributes to lower emissions.
For enhanced performance, certain OM651 variants are equipped with a compact two-stage boost module (excluding the GLK model). This system comprises a small high-pressure turbocharger and a large low-pressure turbocharger, arranged in series. The system intelligently regulates combustion air supply using both turbochargers as needed. This ensures optimal cylinder filling, resulting in higher torque output even at low engine speeds, improving responsiveness and overall driving experience.
Exploring the OM651 Engine Block Head
An exploded view diagram showcasing the components of the Mercedes-Benz OM651 engine block head, highlighting key parts like camshafts, chain, and injectors.
The image above details the components within the OM651 engine block head, crucial for understanding its operational mechanics. Key components include:
- Chain guide: Ensures the smooth and accurate path of the timing chain.
- Chain (Timing Chain): Connects the crankshaft and camshafts, synchronizing valve timing.
- Sprockets (Stars): Gears that the timing chain engages with on the camshafts and crankshaft.
- Intake Camshaft: Controls the opening and closing of the intake valves, regulating air intake.
- Exhaust Camshaft: Controls the opening and closing of exhaust valves, managing exhaust gas expulsion.
- Sensor: Various sensors monitor engine parameters for optimal performance and diagnostics.
- Roller Rocker Arm: Transfers camshaft motion to the valves, reducing friction and wear.
- Hydraulic Compensator (Hydraulic Lifters): Maintains zero valve lash, ensuring quiet and efficient valve operation.
- Chain Tensioner: Keeps the timing chain taut, preventing slack and ensuring accurate timing.
- Leading Sprocket (Leading Star): The primary sprocket driving the timing chain.
Understanding these components provides insight into the complexity and precision engineering within the Mercedes-Benz OM651 engine head.
Common Disadvantages and Reliability Issues of the OM651 Engine
Despite its advanced engineering, the Mercedes OM651 engine has faced certain reliability issues that potential owners and mechanics should be aware of.
-
Piezo Injector Problems (Early Models): As previously mentioned, OM651 engines produced before 2011, particularly higher-performance versions, initially used Delphi fuel systems with piezo injectors. These injectors were prone to leaks, which in severe cases could lead to water hammer and piston damage. Mercedes-Benz addressed this with a recall campaign to replace them with more reliable electromagnetic injectors. Engines with Bosch fuel systems and electromagnetic injectors generally do not suffer from this issue.
-
Crankshaft Bearing Issues (Crank Liners): A significant number of OM651 engine owners have reported issues with crankshaft bearing failure, often referred to as “crank liners.” This issue is frequently attributed to oil dilution caused by a clogged heat exchanger or low lubrication pressure due to a failing variable displacement oil pump. A temporary fix sometimes employed is to plug the pump control valve, forcing it to operate at maximum capacity. However, this is not a permanent solution and indicates a more serious underlying problem.
-
Timing Chain Tensioner and Wear: The combined timing drive, while robust, has its vulnerabilities. The timing chain itself is durable and can last up to 300,000 km. However, the hydraulic tensioner for the timing chain is known to fail prematurely. Replacing this tensioner is a labor-intensive and costly repair.
-
Intake Manifold, Injector, and Oil Leakage Issues: Several smaller but common issues include cracks in the plastic intake manifold, injectors becoming stuck in the cylinder head, and oil leaks from the oil cooler gasket. These issues, while perhaps less catastrophic than major engine failures, can still lead to maintenance costs and inconvenience. Additionally, bi-turbo versions and the plastic oil pan have also been identified as potential weak points.
Vehicle Applications of the Mercedes-Benz OM651 Engine
The OM651 engine has been widely utilized across a broad spectrum of Mercedes-Benz models, demonstrating its versatility and adaptability. It can be found in the following vehicles:
- Mercedes A-Class: W176 (2012 – 2018)
- Mercedes B-Class: W246 (2011 – 2018)
- Mercedes C-Class: W204 (2008 – 2015), W205 (2014 – 2018)
- Mercedes CLA-Class: C117 (2013 – 2018)
- Mercedes CLS-Class: C218 (2011 – 2018)
- Mercedes E-Class: W212 (2009 – 2016)
- Mercedes GLA-Class: X156 (2013 – 2019)
- Mercedes GLC-Class: X253 (2015 – 2019)
- Mercedes GLK-Class: X204 (2009 – 2015)
- Mercedes M-Class: W166 (2011 – 2018)
- Mercedes S-Class: W221 (2011 – 2013), W222 (2014 – 2017)
- Mercedes SLK-Class: R172 (2012 – 2017)
- Mercedes Sprinter: W906 (2009 – 2018), W907 (since 2018)
- Mercedes V-Class: W639 (2010 – 2014), W447 (2014 – 2019)
This extensive list highlights the OM651’s role as a workhorse diesel engine for Mercedes-Benz, powering everything from compact cars to large vans and luxury sedans. Its widespread use underscores its significance in the Mercedes-Benz lineup and the automotive industry.
In conclusion, the Mercedes-Benz OM651 engine is a sophisticated and widely used diesel engine, offering a blend of performance and efficiency. While it has faced some reliability challenges, particularly in its early iterations, understanding its specifications, features, and potential issues is crucial for owners, mechanics, and anyone interested in Mercedes-Benz engineering.
