Engine Mercedes OM629

Engine Mercedes OM629

Mercedes OM629 is a 4-liter, 8-cylinder V-shaped internal combustion diesel engine. The engine has a direct fuel injection system (Common Rail) and a turbocharger. The engine was installed on the largest and most expensive models of the Mercedes-Benz concern from 2005 to 2010. The motor was delivered in a single version OM629DE40LA.

The OM 629 engine, like its predecessor OM 628, has a displacement of 3996 cc. The cylinder block is made of cast 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 outlet gas recirculation system and a balance shaft in the camber of the cylinder block.


Engine’s type diesel
Start of release 2005
Power, kW at rpm 225-235 at 4000
Power, hp at rpm 306-320 at 4000
Displacement, cc 3996
Number of cylinders 8
Number of valves 32
Torque output, Nm 700-730
Compression 17,0:1
Cylinder bore, mm 86
Piston stroke, mm 86
Configuration V
Cylinder head DOHC
Timing mechanism chain
Fuel type diesel fuel
Combustible mixture supply direct injection
Euro standards Euro 4
Cooling liquid

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.

Engine Mercedes OM629 under the hood
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 inlet by 25%.

Frequent problems of the OM629 engine

The OM 629 diesel engine has become more reliable than its predecessor, but still a lot of trouble. The main problems are associated with fuel injectors and high pressure fuel pump failures. The engine quickly cokes, this concerns the outlet gas recirculation system. Also, the engine is afraid of overheating, from which scuffs and cracks are formed, leading to an increased pressure of crankcase gases, which serves as the main indicator of the need for engine overhaul. On a run of 200,000 km, the turbine often fails and the gas distribution chain is stretched.

Explanation of OM629 marking

OM Heavy Fuel Oil (Diesel) ICE
629 Engine type: 8-cylinder

Leave a Reply

Your email address will not be published. Required fields are marked *