Starting in 1997, Mercedes began production of the 1.7-liter OM668 diesel engine, used exclusively for the miniature A-Class. The unit was in the series until 2005, and was presented in five available variants with outputs in the range of 60-95 “horses”.
Structurally, the motor corresponded to the trends of the German brand of the 90s, offering a timing chain and a pair of camshafts with four-valve cylinders. Supercharging is provided by a KKK compressor, and for all versions except the base version there is an intercooler for better cooling.
Mercedes OM668 1.7 CDI engine specifications
The Mercedes OM668 1.7 CDI engine is a diesel engine developed for compact Mercedes cars such as the A-Class (W168). It is characterized by reliability, moderate power and economy, which makes it in demand among drivers who value durability and efficiency.
The OM668 engine is available in two basic versions: OM 668 DE 17 LA red. (160 CDI) and OM 668 DE 17 LA (170 CDI). Both versions have the same displacement and design features, but differ in power and torque.
OM 668 DE 17 LA red. (160 CDI)
- Determined displacement: 1689 cm³
- Power system: Common Rail
- Power: 60 – 75 hp
- Torque: 160 Nm
- Cylinder block: aluminum, 4-cylinder (R4)
- Cylinder head: aluminum with 16 valves
- Cylinder bore: 80 mm
- Piston stroke: 84 mm
- Compression ratio: 19.5
- Special features: exhaust gas recirculation (EGR)
- Turbocharger: BorgWarner K03
- Transmission timing: chain
- Hydrocompensators: yes
- Fasoregulator: none
- Fuel type: diesel
- Environmental class: EURO 3
- Oil: 4.5 liters 5W-30
- Life expectancy: approx. 250,000 km
Version OM 668 DE 17 LA (170 CDI)
- Determined displacement: 1689 cm³
- Power system: Common Rail
- Power: 90 – 95 hp
- Torque: 180 Nm
- Cylinder block: aluminum, 4-cylinder (R4)
- Cylinder head: aluminum with 16 valves
- Cylinder bore: 80 mm
- Piston stroke: 84 mm
- Compression ratio: 19.5
- Special features: EGR, intercooler.
- Turbocharger: BorgWarner K03
- Transmission timing: chain
- Hydrocompensators: yes
- Fasoregulator: none
- Fuel type: diesel
- Environmental class: EURO 3
- Oil: 4.5 liters 5W-30
- Life expectancy: approx. 240,000 km
Design features
Both versions of the OM668 engine are equipped with the Common Rail system, which provides precise, high-pressure fuel injection to help save fuel and reduce emissions. The BorgWarner K03 turbocharger helps increase engine power by providing additional air to the cylinders, which significantly improves acceleration dynamics.
EGR (Exhaust Gas Recirculation) reduces emissions by mixing a portion of the exhaust gases with incoming air for cleaner combustion. The 170 CDI version additionally features an intercooler that cools the air from the turbocharger, improving engine efficiency.
Reliability and maintenance
The OM668 engine has an average service life of 240,000 to 250,000 kilometers, making it a reliable unit if maintenance recommendations are followed. The aluminum cylinder block reduces the overall weight of the engine, which is 136 kg, which has a positive effect on the vehicle’s handling.
It is recommended to use 5W-30 engine oil in the volume of 4.5 liters to maintain stable engine operation. The technical characteristics of the motor allow it to meet EURO 3 standards, which is important for cars operated under strict environmental regulations.
Resource and problems
In general, German motorists have managed to create a reliable engine that is unpretentious in operation. Against the background of the gasoline M166, also used for the Mercedes A-Class, the troubles with the motor on heavy fuel are much less. The disadvantage can be called only not very convenient maintenance, requiring in many cases to lower the engine on the subframe. As a result, car services often simply refuse to repair the OM668.
Generator
One of the weakest places of the German car, almost every owner of A-Class has to change the generator on his car. Problems are associated not only with the wear of brushes and failure of relays, but also with the destruction of shaft bearings. The cost of repair or complete replacement is not so great, but the process of dismantling and subsequent installation is characterized by laboriousness and a lot of inconvenience.
Shaft Sensors
The reliability indicators of the sensors are not bad, but their breakdown can happen. It is worth paying attention to their condition in cases when starting the engine “hot” is associated with difficulties, and the on-board computer indicates the presence of error P1354 (unsynchronized receipt of information from the sensors). In most cases, it is sufficient to change the sensor, but it is also possible that the main cause of the problem is excessive stretching of the timing chain. The “targets” of the sensors can also be damaged, but this is possible only in the case of engine repair and inaccurate assembly work.
Flow meter
Failure of the flow meter, which is responsible for monitoring the engine load, is indicated by error P0100 and a significant increase in voltage, which is no more than 1W under normal conditions with the engine off.
The pressure sensor, responsible for monitoring the state of the intake, is located directly on the engine panel, and is connected to the manifold by a rubber hose, which eventually cracks and begins to leak air. The result is loss of traction when driving at high speeds and rpm.
If the sensor itself is broken, the electronics will indicate the presence of error P1330. A similar error is displayed in situations where the sensor is contaminated, and a simple cleaning with flushing allows you to cope with the problem.
VAC valve
The valve, together with the oil separator, is mounted directly on the valve cover. The valve itself, which is responsible for maintaining optimum pressure, is diaphragm valve. It is characterized by high reliability and a long service life. The appearance of cracks on the diaphragm is noted only after several hundred thousand kilometers traveled.
Very resourceful and oil separator. With significant engine mileage, it is enough to simply wash the part in a solvent, and it will serve without problems for more than one year.
In cases where the intake begins to penetrate oil, it is necessary first of all to check the integrity of the membrane of the valve VKG.
Attachment belt rollers
Indicators of wear resistance of rollers are very modest, so for cars with mileage from the change is almost a guaranteed procedure. It is characteristic both for diesel and gasoline versions of A-class. For the most part, the tensioner roller is the first to start rattling. The replacement process is very labor-intensive, and is associated with the need to slightly lower the subframe. When choosing rollers, experts advise to pay attention only to the original products with a bracket in the set. Despite the higher cost, they are more durable than analogs.
When replacing only the rollers without a bracket, it will be necessary to check for alignment. The slightest damage to the brackets in the process of operation will not allow such a replacement, requiring the purchase of an original set.
Heat exchanger
One of the common problems of the OM668 engine is the appearance of oil leaks in the space between the filter and the heat exchanger. At the junction of the two elements, gaskets are used. According to their wear, it is not difficult to replace them, and the cost of consumables is small.
Turbocharger
Used compressor KKK K03-19 is quite successful, but it is not 100% protected from the occurrence of malfunctions. The very first sign of malfunctions with the turbine is a deterioration of engine thrust and pronounced black smoke from the exhaust. More often than not, the turbocharger rotor loosens over time, backlash occurs, and the impeller clings to the housing. As a result, the oil on the shaft penetrates into the intake, which causes soot from the exhaust.
Fuel Pressure Regulator
The regulator used, mounted directly on the fuel ramp, is completely identical to the one on the OM611 engine. If there are problems with its performance at idle, there is instability of the engine. Replacing the valve with a new one is not very difficult even in the conditions of limited volume of the under-hood space of the German car.
Pistons
A distinctive feature of the OM668 motor is the original injectors, which are not suitable for other engines. The extremely simple design of the products, based on the principles of electromagnet, provides them with excellent reliability. Even with long engine operation, they effectively fulfill their duties.
Failure to replace the refractory washers under the nozzle in a timely manner can lead to their burning in their seats. The dismantling process in this case will require much more effort and additional cleaning of both the injectors and the seats.
EGR valve
The operation of the valve is characterized by simplicity and reliability, and replacing it with a plug is not very difficult. In situations where the valve remains in the “open” position after a breakdown, it is impossible to start the engine regardless of the temperature. At the same time, the engine starts without problems.
Problems with the work of EGR are also possible from the electro-vacuum valve. It can be found on any diesel engine of Mercedes cars, so the search for such a valve will not be a problem.
TNVD
German engine OM668 became one of the pioneers of Common Rail injection system implementation. The main element of the system is the Bosch CP1 pump, borrowed without changes from the OM611.
Characteristic features of the fuel injector are unsurpassed reliability and durability. In particular, plungers have many times longer life than traditional rubber seals, so replacement of the latter is the most common type of repair work. In case of significant wear, fuel may leak from under the pump cover.
The timing chain
Claims to the quality of the chain and its reliability are much less than for the gasoline motor M166, also installed on the youngest of Mercedes. It is put on the gear of the intake camshaft, while the rotation of the camshaft at the exhaust is carried out by means of a gear train.