The 4.0-liter Mercedes OM629 diesel engine was produced by the company from 2005 to 2010 and was installed only on the largest and most expensive models of the concern, such as W211, W221 and X164. The motor was offered in a single version of the DE 40 LA, but with different indexes: 420 CDI and 450 CDI.
The diesel V8-family includes: OM628, OM629.
The OM 629 engine, like its predecessor OM 628, has a displacement of 3996 cc. The cylinder block is made of aluminum with cast iron liners. Cylinder spacing is 97 mm and camber is 75° for space reasons. The engine is equipped with variable geometry turbochargers for each cylinder bank, a liquid intercooler, two camshafts per cylinder head (4 valves per cylinder), a cooled exhaust gas recirculation system and a balance shaft in the camber of the cylinder block.
Specifications
| Production years | 2005-2010 |
| Displacement, cc | 3996 |
| Fuel system | Common Rail |
| Power output, hp | 306 – 320 |
| Torque output, Nm | 700 – 730 |
| Cylinder block | aluminum V8 |
| Block head | aluminum 32v |
| Cylinder bore, mm | 86 |
| Piston stroke, mm | 86 |
| Compression ratio | 17.0 |
| Features | intercooler |
| Hydraulic lifters | yes |
| Timing drive | double row chain |
| Phase regulator | no |
| Turbocharging | two GTB1752VK |
| Recommended engine oil | 5W-30 |
| Engine oil capacity, liter | 10.5 |
| Fuel type | diesel |
| Euro standards | EURO 4 |
| Fuel consumption, L/100 km (for Mercedes GL 420 CDI 2007) — city — highway — combined |
15.6 9.2 11.6 |
| Engine lifespan, km | ~280 000 |
| Weight, kg | 280 |
The engine was installed on:
- Mercedes E-Class W211 in 2006 – 2009;
- Mercedes GL-Class X164 in 2006 – 2010;
- Mercedes ML-Class W164 in 2007 – 2010;
- Mercedes S-Class W221 in 2005 – 2010.
Disadvantages of the OM629 engine
- This diesel engine has become more reliable than its predecessor, but still causes a lot of trouble.
- The main problems are associated with pouring fuel injectors and injection pump failures.
- This unit cokes very quickly, especially for the EGR system.
- Also, the engine is very afraid of overheating, from which scuffs and cracks form.
- On a run of 200,000 km, the turbine often fails and the timing chain stretches.
Differences between the OM629 engine and its predecessor:
- increased boost pressure – more power and torque;
- equipped with GTB turbochargers;
- compression ratio 17: 1;
- a new DPF has been installed.
In addition to the above changes, the engine is equipped with new turbines and injection systems with a pressure of 1600 bar, as well as piezoelectric injectors. By reducing the pressure loss in the intake tract, it was possible to increase the volume of air pumped into the cylinders by 15%. And the use of intercoolers made it possible to reduce the temperature of the inflated air to 120° C and increase the density at the engine intake by 25%.
Explanation of OM629 marking
| OM | Heavy Fuel Oil (Diesel) engine |
| 629 | Engine type: 8-cylinder |
