Mercedes-Benz OM639 3-cylinder diesel engine

In the early 2000s, DaimlerChrysler and Mitsubishi joined forces to create a platform for several subcompact cars. This is how the 6th generation Colt and the first Smart ForFour appeared. The main work was done by the Japanese. They also created new gasoline engines of 3A9 and 4A9 families, about which we have already told. For successful sales in Europe, these cars needed a diesel engine. Daimler engineers have just created it. Thus, the turbodiesel on Colt 6 and Smart ForFour is German.

It is a 3-cylinder motor OM639 with a volume of 1.5 liters. It is essentially made from the 4-cylinder 2-liter OM640, which was developed specifically for the A- and B-Class. The pistons of these related diesels are identical, and the fuel injectors are also identical.

The 3-cylinder diesel OM639 was produced for a short time: from spring 2004 to summer 2006. It was offered in two versions with an output of 68 and 95 hp.

Structurally, this engine is created in the classic Mercedes style. The chain is used in the timing drive. The fuel injector is attached to the cylinder head and is driven from the camshaft by an intermediate gear. The cylinder head has two camshafts and there are 4 valves per cylinder. Hydrocompensators are present.

Unlike the OM640 engine, which is installed on the A- and B-class at a 60-degree forward tilt, the younger OM639 is installed almost vertically. And of course, for damping of inertial forces of the first order, the 3-cylinder engine is equipped with a balancer shaft. Well, since there was no place for it in the unified block, the balancer shaft is placed in a separate housing and screwed to it from the side.

The balancer is driven by the oil pump chain and rotates at the speed of the crankshaft in the opposite direction – the intermediate gear is responsible for “turning”. The supports of the balancer are lubricated with oil. Oil filter and heat exchanger are mounted on its body.

The OM639 engine received the second generation Common Rail fuel system from Bosch. Especially for this engine and 4-cylinder OM640 were developed more compact (short) injectors, injecting fuel in two stages at a pressure of 1600 bar.

Technical data

Problems and reliability of the OM639 engine

The engine turned out to be rather compromise. Unpleasant breakdowns with it happened already at a mileage of 100 000 km. It is also known quite a few cases of serious wear, because of which the engine was either overhauled or replaced with a contract one.

The OM639 engine does not start

If the diesel Smart ForFour or Mitshubishi Colt does not start – namely, if the engine does not “spin” at all, it is necessary to check the starter and high-voltage wires to it. The wires and their terminals are badly corroded and simply break off. In addition, the starter itself is flimsy: rotor bearings fail or the bendix stops working because of burning contacts in it.

Oil separator

Right on the valve cover of the OM639 engine there is a labyrinth oil separator housing. Its size for such an engine is quite impressive, and it is not quite clear what it is connected with. By the cleanliness in it, you can judge the condition of the engine, the volume of crankcase gases. Unfortunately, abundant resinous deposits in it and in the ventilation valve are not uncommon.

Resinous deposits clog the oil separator, after which there are serious problems with crankcase gas pressure. They literally support the pistons from below and disturb the oil rings – the oil they remove does not flow down into the crankcase. This causes oil consumption for carbon monoxide.

At the same time, because of burning oil, the temperature in the combustion chamber rises, soot forms on the pistons and valves, heat dissipation deteriorates. And there is a problem with the cylinder head.

Turbine

On the German 3-cylinder diesel engine was installed Japanese turbine IHI RHF3, without controlled geometry, just with a bypass valve. This turbine has been noticed to have a jamming of the bypass valve. In this case, the engine can alternately stall, not give full power, and then drive like a chipped engine – that is, feel, with more power. This is due to a malfunction of the bypass valve actuator.

Also, this tiny turbine can churn oil into the intake, which also negatively affects combustion chamber temperatures.

Turbo to intercooler

Quite often the pipe from the turbine to the intercooler tears from the side of the turbine. The collars on both ends of the pipe also loosen and harden. This can be noticed by slight oil misting. In both cases, turbine underblowing occurs: air simply “escapes” through a rupture or leaky seals.

EGR valve

Malfunctions with the EGR valve on the OM639 engine occurred long before the 100,000 km mileage. The valve simply jams open due to soot and oil deposits. In this case, the diesel engine is deprived of a significant proportion of air, the fuel does not burn completely, and black smoke comes out of the exhaust. As usual, the valve can be cleaned. Or it can be plugged with a re-flashing.

Almost all versions of the OM639 engine used a vacuum-controlled EGR valve from the manufacturer Pierburg (A6391400160). Only in the last months of production was it replaced by an electronically servo-operated valve from Wahler (A6391400460). A similar valve was used on the C-, E- and S-Class diesel engines.

Ignition spark plugs

The OM639 engine had short-lived glow plugs, they failed at a mileage of 100,000 – 150,000 km. At least one spark plug failure is indicated by the glow plug indicator light on after starting the engine. The plugs are difficult to unscrew, quite often they are broken.

Cylinder Head

An uncommon problem of OM639 diesel engine at the mileage of about 150 000 km is the appearance of cracks in the cylinder-head. Most likely, they occur due to the increase of temperature in the combustion chambers against the background of oil consumption.

Timing chain

The OM639 (and OM640) engine is equipped with a timing chain from the predecessor motor OM668 with a volume of 1.7 liters. It runs very well and is usually not stretched.