How long can a Mercedes diesel engine last?


This article will answer the following questions: how long can a Mercedes diesel engine last? What are the materials and moving parts inside a Mercedes diesel engine? What are the newly developed diesel engines used in Mercedes Benz passenger cars?

How long does a Mercedes diesel engine last?

Records indicate that a Mercedes diesel engine can last for more than one million kilometres- provided it has been maintained and used properly. Mercedes Benz engines have great built quality and they are lighter in weight and power output is also more than other brands. The Mercedes Benz diesel engine also uses exhaust gas recirculation along with SCR selective catalytic reduction exhaust after treatment to comply with emissions limits. 

During the designing phase, diesel engines are put through rigorous tests. Engines are operated on specially designed test benches and they are subjected to thermal shocks tests to check the integrity of the engine block. The engines are also operated at full load for extended durations, to test the exhaust system components.

The above image shows the OM654 inline 4 cylinder diesel engine currently used in Mercedes Benz passenger cars. OM stands for oil motor which indicates it is a diesel engine. The latest diesel engines used in Mercedes Benz passenger cars are OM 654 and OM 656. The OM656 is an inline six-cylinder with dual-stage turbocharging. 

Materials used in manufacturing engine components.

Engine block or commonly known as crankcase is the foundation of any engine. Traditionally diesel engine blocks are made up of cast iron because diesel engines are self-igniting, the compression pressure in a diesel engine is up to 30 bars. Hence, the material of the engine block must be strong enough to sustain high combustion pressure.

However, thanks to the use of the latest manufacturing technology and high-pressure fuel injection system with 8 holes piezo injector, the crankcase of the latest generation of Mercedes Benz diesel engine is made up of special aluminium alloy. The use of the aluminium crankcase has helped greatly in the weight reduction of the engine. 

Closed deck engine construction is more commonly used in Mercedes Benz diesel engines. This type of construction provides more support to the cylinder walls and water jackets can be designed around the cylinder sleeve for better cooling. The use of closed deck design along with cast iron metal makes up for heavy engines.

1- Piston pin 2- combustion cavity 3- connecting rod

The pistons are also made of steel with stepped combustion cavities. The narrow piston compression area allows maximum air efficiency and thereby reduces soot levels. The crankshaft is also forged with a de-axiated arrangement of cylinder barrels towards the cold side of the engine.

Cylinder heads of diesel engines are constructed using a special alloy of aluminium-silicon metal. The cylinder head houses intake and exhaust valves, rocker arms with rollers and hydraulic lifting elements. Camshafts are partially mounted in the cylinder head and cylinder head cover. Therefore the cylinder head cover cannot be replaced separately. The cylinder head must also be replaced together with the cylinder head cover.

Mercedes Benz uses NANOSLIDE coating on the cylinder walls. This is an extremely thin coating applied to the inner surface of the cylinder to reduce friction between the piston. Twin-wire arc spraying (TWAS) is used to spray an extremely thin coat of iron-carbon alloy on the cylinder walls.  The friction between the piston and piston rings is reduced by almost 50 per cent.

Lubrication of moving parts inside the engine.

When the engine is running, pistons connecting to the crankshaft are reciprocating inside cylinder walls. The crankshaft is rotating inside the crankcase on the main bearing. The crankshaft is used to convert the reciprocating motion of a piston into a rotating motion which is used to drive the transmission. 

There is an intricate lubricating circuit inside the engine block and cylinder head. The oil pump circulates engine oil inside the oil sump to all the moving parts of the engine. Engine oil reduces friction between the moving parts and prevents premature wear of critical engine components.

Like the lubricating circuit, there is also a coolant circuit in an engine. Water pumps circulated coolant between radiation and the engine block. It is very important to maintain the engine at the desired operating temperature. Coolant is usually a mixture of water and antifreeze or an anti-corrosion solution. 

A special feature found in Mercedes Benz diesel engines

  • Warm-up phase- When the engine is started for the first time, engine oil and coolant temperature are low. The engine is designed to operate at a specific operating temperature and must also reach this operating temperature quickly regardless of the outside temperature. Hence, in the warm-up phase, the engine idles at slightly higher RPMs for a few minutes after starting the engine. This also ensures the engine oil is circulated to the entire engine.
  • Radiator shutters- aerodynamic flaps are not only present on the outside of the vehicle but also inside the vehicle. Flaps cover the surface of the radiator and are operated by a vacuum actuator. 

By closing the flaps air does not flow over the surface of the radiator and coolant can heat up faster which is then pumped back into the engine and the operating temperature is reached more quickly.

  • Preheating system- Preheating system is made up of glow plugs, each one for an individual cylinder. The combustion chamber is heated up before the engine is started. Preheat system also uses an exhaust gas recirculation bypass flap. The exhaust gas is not hot during the warm-up phase and can be directed into the combustion chamber without cooling.

Engine service and repairs

In Mercedes Benz, passenger cars service intervals are every 15000 km or 1 year whichever comes early. During service of the engine, the engine oil and oil filter is replaced. If the vehicle is used in dusty areas, air filters are also replaced.

If the engine oil and oil filter is not replaced periodically then engine oil loses its lubricating properties and can no longer do an adequate task of lubricating moving parts. Engine oil filter is also a very critical component as it filters small metal shavings in engine oil which can scratch and damage bearings inside the crankcase. Small particles if left unfiltered in the engine can block the lubricating path or oil spray nozzles and cause wear to components like timing chain, valves, connecting rods and cylinder walls.

If the vehicle is driven through the water, the engine can suck water from the intake port and as water is an incompressible fluid, it will damage the engine and cause the hydrostatic lock. Such an engine needs to be rebuilt, authorised parts are available at the dealerships and after repairs, the engine can last for the entire service life of the vehicle. Engine blocks with NANOSLIDE coating must not be resleeved and reused. The entire block or in some cases complete engine must be replaced.

Following are a few tips while operating the engine.

  • After starting the engine, wait for a few seconds so the warm-up phase can finish. This also makes sure the engine oil is circulated entirely in the engine.
  • Never operate the engine in full loads for an extended duration, keep the RPMs fluctuating. Operating an engine at constant or high rpm puts unnecessary strain on the engine components.
  • Visually inspect the engine compartment for visible oil or coolant leaks. If the oil or coolant level is low then the engine can be damaged due to overheating.
  • Consult the workshop if an EOBD malfunction or abnormal noise is coming from the engine while driving.
  • Follow the service schedule and replace parts like air filters, fuel filters etc so the engine can continue to function properly.

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Mercedes Benz diesel engines are rigorously tested and built with an advanced manufacturing process. If the engine is maintained, it will continue to function for more than 10 years. Authorised parts are also available if the engine moving parts are worn out or damaged. Performing repairs at an authorised service centre guarantees the longevity of the engines. Adblue injection system with selective catalytic reduction exhaust systems also make sure the diesel engine comply with future emission laws

FAQs How long can a Mercedes engine last

Can a Mercedes diesel engine last forever?

If the engine is serviced regularly and not abused by driving under full load conditions, it can last forever. The life of an engine directly depends on driving conditions and maintenance.

Do Mercedes engines break down a lot?

Mercedes Benz engines are thoroughly tested before they are put in production. Under normal operating conditions the Mercedes engine does not breakdown.

Is it expensive to service a Mercedes Benz?

Yes, Mercedes Benz service costs are high as they use special engine oil and the cost of the spare parts required for servicing are not cheap. However, star ease service packages are available which provides a great benefit if the vehicle covers more than 100000 km within a year

Is it worth buying a 10-year-old Mercedes?

Yes, it is worth buying a 10-year-old Mercedes. The build quality of older Mercedes vehicles is very good, spare parts are also easily available to restore the vehicle. Always check the service history of the vehicle before buying the car.

What is DPF and SCR in Diesel engines?

DPF stands for diesel particulate filter and SCR stands for selective catalytic reduction. DPF is used before SCR to filter out soot particles. Both are part of exhaust gas after-treatment.