Mercedes-Benz OM651 is a family of in-line four-cylinder diesel engines from Mercedes-Benz, first introduced in October 2008. It was created as a replacement for the OM646 and OM642 series. Production took place at a plant in Stuttgart, Germany.
The diesel R4-family includes: OM616, OM601, OM604, OM611, OM640, OM646, OM651, OM654, OM668.
In 2008, Mercedes introduced a new generation of its 4-cylinder diesel units. Here is a cast-iron cylinder block, an aluminum 16-valve cylinder head with hydraulic lifters and a combined timing drive from a roller chain, several gears and balancer shafts. Simple versions of the engine are equipped with an IHI VV20 or IHI VV21 variable geometry turbine, and the most powerful modifications of this engine received a BorgWarner R2S bi-turbo system.
Initially, powerful versions of the diesel were equipped with a Delphi fuel system with piezo injectors, which caused a lot of trouble, and since 2010 they began to be changed to electromagnetic ones. And since 2011, a revocable campaign began to replace injectors for previously produced units. Basic engine modifications have a Bosch fuel system and electromagnetic injectors.
Available in DE18 LA (1796 cc) and DE22 LA (2143 cc) versions. Despite the fact that most variations of the power unit have a working volume of 2143 cc, nevertheless, its power varies in the range from 107 hp to 204 hp. Versions above 125 kW (170 hp) are equipped with a twin turbo system, below 100 kW with a single turbocharger.
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|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)
|Timing drive||chain & gears|
|Recommended engine oil||5W-30|
|Engine oil capacity, liter||6.5 (11.5 in commercial models)|
|Euro standards||EURO 5/6|
|Fuel consumption, L/100 km (for Mercedes E 250 CDI 2015)
|Engine lifespan, km||~400 000|
The engine was installed on:
- Mercedes A-Class W176 in 2012 – 2018;
- Mercedes B-Class W246 in 2011 – 2018;
- Mercedes C-Class W204 in 2008 – 2015; C-Class W205 in 2014 – 2018;
- Mercedes CLA-Class C117 in 2013 – 2018;
- Mercedes CLS-Class C218 in 2011 – 2018;
- Mercedes E-Class W212 in 2009 – 2016;
- Mercedes GLA-Class X156 in 2013 – 2019;
- Mercedes GLC-Class X253 in 2015 – 2019;
- Mercedes GLK-Class X204 in 2009 – 2015;
- Mercedes M-Class W166 in 2011 – 2018;
- Mercedes S-Class W221 in 2011 – 2013; S-Class W222 in 2014 – 2017;
- Mercedes SLK-Class R172 in 2012 – 2017;
- Mercedes Sprinter W906 in 2009 – 2018; Sprinter W907 since 2018;
- Mercedes V-Class W639 in 2010 – 2014; V-Class W447 in 2014 – 2019.
The compact, low design, thanks to the rear camshaft drive, contributes to the fulfillment of legal requirements for pedestrian protection.
The 4th generation common rail direct injection with piezo injectors (which Mercedes replaced with conventional ones as part of the service program, because they turned out to be problematic) provides an injection pressure of up to 2000 bar. Direct control of the injector needle creates the conditions for high flexibility in injection timing and smooth engine operation, as well as high performance with low fuel consumption and low exhaust emissions.
The geometry of the flat combustion chamber and the lower compression pressure reduce the emission of raw exhaust gases, especially nitrogen oxides. The maximum cycle pressure of up to 200 bar increases engine performance and contributes to the reduction of harmful emissions.
The compact two-stage boost module (not on the GLK) consists of a small high-pressure turbocharger and a large low-pressure turbocharger. Each of them consists of a turbine connected in series and a compressor driven from it. The combustion air supply is regulated as required using both turbochargers. This ensures a better filling of the cylinders and, as a result, a higher torque already at low revs.
OM 651 engine block head
- Chain guide;
- Intake camshaft;
- Exhaust camshaft;
- Roller rocker arm;
- Hydraulic compensator;
- Chain tensioner;
- Leading asterisk.
Disadvantages of the OM651 engine
- Until 2011, the main versions were equipped with a Delphi fuel system with piezo injectors, which were prone to leaks, which often led to water hammer with piston burnout. There was even a revocable campaign to replace them with simpler electromagnetic ones. Engine modifications with a Bosch fuel system have no reliability problems.
- Many owners of cars with such a diesel engine are faced with cranking liners. This is caused by dilution of superheated oil due to a clogged heat exchanger or a drop in lubrication pressure due to a failed variable displacement oil pump. You can insert a plug into the pump control valve and it will work at maximum.
- The combined timing drive here consists of a roller chain and several gears. Moreover, the chain can serve up to 300 thousand km, but its hydraulic tensioner is often rented much earlier, and replacing this tensioner is quite laborious and expensive.
- A lot of trouble in this diesel engine is delivered by cracks in the plastic intake manifold, injectors sticking to the cylinder head and an oil cup that is always leaking over the gasket. The weak points of the motor also include bi-turbo version turbines and a plastic pan.