Innovative engineering from Mercedes-Benz once again provides trendsetting impetus in passenger car diesel technology. The world’s pioneer in diesel technology from Stuttgart is the first to replace the hitherto conventional aluminium pistons in passenger car diesel engines with a new high-tech generation of pistons made of steel. The advantages they bring, when combined with the innovative NANOSLIDE® cylinder bore coating technology, include even lower fuel consumption and even lower CO2 emissions.

Aluminium piston (left) the new steel piston (right)

In 1936 Mercedes-Benz became the first company in the world to launch a diesel passenger car, thus taking on its role as a diesel pioneer. Stuttgart’s automotive engineers consistently reinforced this leadership position over the decades that followed through the introduction of numerous technical innovations that have contributed significantly to making the passenger car diesel engine what it is today: powerful and yet economical – in short, efficient.

The engineers are now once again working to tighten the efficiency screw. In September 2014, new high-tech steel pistons will be celebrating their world premiere in a standard-production passenger car, in the V6 diesel engine of the Mercedes-Benz E 350 BlueTEC. Thanks, amongst other things, to this technical innovation the saloon continues to deliver the same engine output (190 kW/ 258 hp), yet only uses around 5.0 litres of diesel fuel per 100 kilometres – the saving achieved through the use of the steel piston is thus around three percent.

Steel pistons are already commonly found in commercial vehicle engines, where they are combined with heavy cast-iron crankcases, while aluminium pistons have over the years gradually become the norm for passenger car diesel engines. The high-tech steel pistons that Mercedes-Benz has now developed completely from scratch harmonise perfectly with the state-of-the-art and much lighter aluminium engine housings and the multiple-award-winning NANOSLIDE® cylinder bore coating technology also developed by Mercedes‑Benz.

Exploiting material advantages

Steel and aluminium have significantly different characteristics: steel expands less than aluminium when hot, conducts heat less well and is simply heavier. At first glance, this would seem to make the combination of aluminium housing and steel pistons tricky. Notwithstanding this situation, the Mercedes-Benz engineers discovered opportunities for the future by using the apparent differences between the properties of the respective materials to their best advantage.
They exploited the fact that a steel piston only expands with heat to about a quarter of the extent of its aluminium equivalent to fit the steel piston more tightly within the aluminium housing, with the effect that it sits very snugly in the cylinder bore. However, as the temperature rises during operation of the engine, the aluminium housing expands more than the steel piston – and the result is greater tolerance of the piston within the cylinder and thus less friction. As the piston/cylinder assembly alone causes between 40 and 50 percent of the mechanical friction, the potential for efficiency revealed here was significant.

Stronger, smaller, light

The steel pistons used up until this point were, however, little suited for the combination with engine housings made of aluminium. So instead, Mercedes‑Benz had to redesign the piston. The modern versions of the steel pistons that will now be fitted for the first time as standard in the V6 diesel on board the E 350 BlueTEC, within an aluminium crankcase with NANOSLIDE® cylinder bore coating technology, are high-tech components forged out of high-quality, high-strength steel. The challenge for the piston supplier is considerable, since the manufacturing process for the new, high-strength steels is similarly complex.

But the effort is worthwhile, as the higher strength of the modern steel allows for a more compact piston design, which more or less compensates for the fact that the material is around three times as dense. Indeed, the innovative steel pistons that will in future be working away within the six combustion chambers of the Swabian V6 diesel engine are as much as 13 millimetres lower than the aluminium equivalents used until now (aluminium pistons in the V6 diesel approx. 71.6 mm high, steel pistons only 58.6 millimetres). Thanks to this changed geometry and intelligent design, the weight of the unit comprising piston, gudgeon pin and piston rings is on a par with that of the version with aluminium piston. Mercedes-Benz has thus been able to compensate almost completely for the weight disadvantage of steel and even to ensure reserves of strength for peak pressures that may become even higher in future.

High efficiency, low consumption

At the same time the use of steel pistons has enabled the engineers to improve the level of efficiency, since the lower thermal conductivity of steel compared with aluminium means that higher temperatures are reached within the combustion chamber. The ignition quality thus increases, while the combustion duration is reduced. The result is lower fuel consumption and pollutant emissions. Mercedes-Benz took account of the lower thermal conductivity of steel with design modifications such as modified cooling ducts in the pistons.

Experience has shown that the innovative steel pistons optimise thermodynamic performance and, at the same time, reduce friction significantly. Furthermore, measurements showed that in the lower and middle speed ranges, so important in everyday driving, significant consumption benefits can be achieved.

Advantage steel

As far as the future is concerned, the engine designers at Mercedes-Benz see further possible advantages in the use of the high-tech steel pistons:
Steel not only allows the piston to be made smaller, but also offers greater reserves for coping with mechanical stresses. This is particularly advantageous for further downsizing concepts

Since steel pistons are stronger than aluminium ones, a diesel engine fitted with them can operate at higher temperatures and thus achieve a higher level of thermodynamic efficiency.

Since the lower thermal expansion of steel pistons compared with aluminium also means that the engine designers are able to reduce the gap between the cylinder wall and the piston as far as the first piston ring, it has been possible to reduce both pollutants and untreated emissions.

Logical further development

These innovative steel pistons mark a logical next step in Mercedes-Benz’s work to further develop diesel technology. As they have done so often in the past, proving themselves to be true diesel pioneers at every step of the way, the Stuttgart engineers continue to work on making the diesel engine a viable proposition for the future.

The V6 diesel engine, for example, which will now be going into series production with the new steel pistons for the E 350 BlueTEC, has been through various stages of development since its first appearance in the W212 in 2008. It also benefits from a further innovation developed by Mercedes-Benz: NANOSLIDE® cylinder bore coating technology. This technology was pioneered by Daimler in 2006 in the AMG V8 petrol engine. It uses twin-wire arc spraying (TWAS) technology to melt iron/carbon wires, which it then sprays onto the inside cylinder walls of the lightweight aluminium crankcase with the help of an inert gas flow. Very fine finishing of the resulting nano-crystalline iron coating creates an almost mirror-smooth surface with fine pores, which reduces friction between the piston assembly and the cylinder wall compared with when cast-iron cylinders are used, while also being extremely resistant to wear. Further benefits: lower engine weight, reduced consumption and CO2 emissions.

All in all, the V6 diesel from Mercedes-Benz today generates significantly lower CO2 emissions than it did in its previous appearances in the E-Class. In 2009 the combined figure for the emissions from the E 320 CDI was 179 grams of CO2 per kilometre; in the next-stage E-Class of 2013 this figure was 144 grams, combined. Thanks to the use of the steel piston, amongst other things, the figure for the E350 BlueTEC is now well below 140 grams. In a parallel development, the output has increased since 2008 from 155 kW (211 hp) to the current 190 kW (258 hp).

Mercedes-Benz a step ahead in diesel technology

It is envisaged that the new pistons will very shortly also be in use in Mercedes-Benz’s four-cylinder diesel engines. Joachim Schommers, head of basic engine development at Mercedes-Benz: “We are assuming that pistons made of steel will in future also be in widespread use in passenger car diesel engines.”

Check out the latest photos of the Mercedes-Benz A-Class tuned by Brabus.  In addition to the interior and exterior updates, Brabus increased the diesel engines output to 155 kW/ 210 HP, 410 Nm.  The changes to the engine propels the A220 0-62 mph in 7.9 seconds, up .3 seconds from the factory claim, with a V-Max of 142 mph.

Downsizing for the entry-level engines and downspeeding for the more powerful units – that is the Mercedes-Benz strategy for the diesel engines in the new A-Class. The wide range meets every performance requirement, and demonstrates the potential residing in the diesel engine: for the first time – with the A 180 CDI – a Mercedes-Benz will emit just 98 g of CO2 per kilometre. As a further highlight, the A 220 CDI already meets the Euro-6 emission standard only coming into effect from 2015.

The diesel engines also boast extreme efficiency and environmental friendliness, thanks to state-of-the-art injection technology and turbocharging. The A 180 CDI kicks off at 80 kW (109 hp) and offers maximum torque of up to 250 Nm (dual clutch transmission) or 260 Nm (6-speed manual transmission). In the A 200 CDI the maximum power output stands at 100 kW (136 hp), accompanied by maximum torque of 300 Nm. The A 220 CDI has a displacement of 2.2 litres and generates 125 kW (170 hp) with 350 Nm of torque, giving the performance of the A-Class a decidedly sporty touch.

From the S-Class to the A-Class: the diesel engines of the OM 651 series

Since its world premiere in 2008 the direct-injection diesel engine known as the OM 651 has been setting standards in terms of performance and torque characteristics, economy, emissions and smooth running. It is in more widespread use than any other Mercedes-Benz diesel engine and serves as a model of efficiency and power right up to the S-Class. For transverse installation the belt drive for the ancillary units, the installed position of the turbocharger and the air ducting have been modified.

No less than three versions are used in the new A-Class:

• Dynamic to drive, extremely efficient and outstandingly clean, the A 220 CDI is only available in combination with the 7G-DCT dual clutch transmission. The 125 kW (170 hp) top diesel is equipped with a weight-optimised crankshaft with individual bearing covers bolted from below and four counterweights, enabling it to tip the scales at around six kilograms less than a longitudinally installed OM 651 of the same displacement. The single-stage turbocharger has larger dimensions than that in the 80 and 100 kW variants. The A 200 CDI has multiple exhaust gas recirculation (see “Under the microscope”) to reduce nitrogen oxide emissions. It already meets the Euro-6 emission standard coming into force from 2015. With 112 g of CO2 per kilometre (provisional figure) the A 220 CDI sets new standards in its segment. With a displacement of 2.2 litres the engine is comparatively large, and therefore already agile at low rpm. “Downspeeding” is the term used by the engine specialists at Mercedes-Benz to describe this combination of a large displacement and low engine speeds. As a result it has been possible to make the ECONOMY mode of the 7G-DCT transmission decidedly economical and comfortable. If the driver selects “S”, gearshifts are performed much faster and the ratio spread uses the rpm reserves of the engine for dynamic performance.The performance of the A 220 CDI – which is available in BlueEFFICIENCY and Sport versions – is at sports car level with 7.8 seconds from zero to 100 km/h and a top speed of 227 km/h.

• The 1.8-litre engine variant is used in the A 180 CDI with the 7G-DCT dual clutch transmission and the A 200 CDI. The displacement was reduced by shortening the stroke (83 mm instead of 99 mm). The significantly longer connecting rods ensure lower transverse friction, and the two Lanchester balancer shafts are also of low-friction design. The single-stage turbocharger was optimised for efficiency and features adjustable vanes. With a distance between cylinders of 94 millimetres and cylindrical gears driving the camshafts, transverse installation and the necessary length restriction were part of the design specification from the very start.

To realise the start/stop function, the belt drive is decoupled from the crankshaft in all three engines.

Other common features include:

• Common rail technology with a rail pressure increased to 1800 bar. The maximum ignition pressure of 180 bar also contributes to the high power output and a muscular torque curve.
• The oil injection nozzles and the water pump are activated only when required, in order to save energy and fuel. The controlled oil pump additionally reduces oil flow and thus fuel consumption.
• The engine block is made of cast iron, the cylinder head of aluminium.
• A two-piece water jacket in the cylinder head provides for optimum cooling in the area of the combustion chamber plate. This enables an ignition pressure of 200 bar and a high specific power output.
• The cast iron barrels have undergone considerably finer honing than on the predecessor, also contributing to the reduction in fuel consumption.
• To compensate for the second-order forces which are inherent to four-cylinder in-line engines there are two Lanchester balancer shafts at the bottom of the engine block running in low-friction roller bearings rather than conventional plain bearings.
• The two-mass flywheel has been specifically designed for high engine torque at low engine speeds in order to isolate the crankshaft’s vibration stimuli, thereby contributing to the engine’s excellent smooth running.

Replete with Mercedes-Benz know-how: the OM 607

For the A 180 CDI with manual transmission Mercedes-Benz has had recourse to its cooperation with Renault to achieve fuel economy advantages from a compact, lightweight, low-friction engine which has been rigorously downsized. The common-rail four-cylinder with a rail pressure of 1600 bar is currently in its sixth generation, with more than 1.3 million units produced each year. This 1.5-litre engine with low-pressure EGR generates 80 kW (109 hp). With 98 g of CO2 per kilometre, it is among the most environmentally friendly diesels in the compact car segment. The turbocharger features variable turbine geometry (VTG).

This engine with the in-house designation OM 607 weighs around 30 kilograms less than an OM 651. Numerous components are specific to Mercedes-Benz, for example the OM 607 has the engine mountings of the M 270 petrol engine, as well as a special two-mass flywheel. The starter flanged onto the transmission, the alternator and the refrigerant compressor also come from the Mercedes modular system, and are driven by a belt with six grooves.

Like all Mercedes engines, the OM 607 was required to absolve the extensive engine test programme involving bench-testing and endurance runs. The application effort devoted to the OM 607 by Mercedes-Benz was very considerable. In a joint project team of Mercedes and Renault personnel the engine was especially improved with respect to NVH and driveability. Coordination work also went into the ECO start/stop function included as standard. This Mercedes-specific feature also operates at temperatures down to minus 10 degrees Celsius, for example, and can therefore make a more frequent contribution to fuel economy.

Overview of technical data for the A-Class with diesel engine

* manual transmission,

** 7G-DCT dual clutch transmission,

*** figures for 7G-DCT dual clutch transmission in brackets

The new Mercedes-Benz SLK 250 CDI marks the continuation of the company’s unique diesel engine heritage, as well as countering the common misconception that diesel engines and sports cars are incompatible. The four-cylinder diesel engine in the SLK Roadster delivers 150 kW (204 hp) from a displacement of just 2.2 litres to give the two-seater its characteristic sporty temperament. The sprint from 0 to 100 km/h (0-62 mph) takes only 6.7 seconds. Apart from all this, the Mercedes SLK 250 CDI is the most economical and therefore the most environmentally compatible roadster in its segment. It is happy with 4.9 litres of diesel fuel per 100 kilometers (63 miles) (NEDC combined consumption).With the diesel engine in the SLK Mercedes-Benz has taken the next step in a successful strategy that began in 1936 with the 260 D model – the world’s very first diesel car. The world’s oldest motor manufacturer has continued to develop these robust and economical engines ever since and, as far back as the mid-1970s, was able to demonstrate their hitherto undiscovered qualities as high-performance units in record-breaking drives with the legendary C111-II D and the C111-III. The new Mercedes-Benz SLK 250 CDI is the logical successor to these illustrious forbears.

A certain sluggishness has been accepted as an intrinsic characteristic of the diesel engine ever since Mercedes-Benz installed one in the world’s first diesel passenger car in 1936. So wrong. Some 40 years later, engineers working for the Swabian manufacturer began to look more closely at the performance potential of the thrifty compression-ignition engine – and soon discovered what they were looking for. They fitted a turbocharger to the standard 80 hp five-cylinder engine found in the 240 D 3.0 and 300 D models to elicit an impressive 190 hp from the 3-litre diesel.

With this powerful diesel engine under the bonnet of a spectacularly styled gull-wing model, painted in bright orange, Mercedes-Benz was soon geared up for some record-breaking drives. The C 111-II D powered its way to some sensational records at the Nardo circuit in southern Italy in 1976. For a whole hour, for example, it circled the high-speed track at anaverage speed of 253.770 km/h. It went on to collect further records in all categories – over distances of 10 to 10,000 kilometres and over periods of 6 to 24 hours.

No one had previously thought a diesel vehicle capable of such performance.

In April 1978, the even more aerodynamically designed C 111-III consigned these records to the scrapheap of history, with what was by that stage a 230 hp diesel engine with exhaust gas turbocharging and charge air cooling. It set a new record over one hour with an average speed of around 320 km/h, while the average over the other record distances also never fell below 314 km/h. No other diesel vehicle had ever even come close to such speeds. With these impressive records under its belt the C 111-III was able, once and for all, to prove the reliability and efficiency of the turbodiesel engine.

While these record-breaking drives were going on, development of the production version of the turbodiesel continued apace. These efforts led in 1978 to the market launch of the 300 SD, the world’s first diesel car with exhaust gas turbocharger.

In 1997 Mercedes-Benz ushered in a new era in diesel technology with the C 220 CDI. This was the first production passenger car to feature a diesel engine with common-rail direct injection. This new technology gave the car a significantly higher output and extra torque, while also setting new standards in the disciplines of fuel consumption and pollutant emissions.

That Mercedes-Benz should now for the first time be offering the sporty SLK Roadster with a diesel engine is the logical next stage in these developments. Its four-cylinder diesel engine, with a displacement of 2143 cc, delivers 150 kW (204 hp) with available torque of 500 Newton metres – as much as a petrol-engined model with more than twice this displacement would normally offer. The new SLK 250 CDIfeatures the most powerful diesel powerplant in this class, with a thrust that propels the Roadster to a very sporty level of performance.

Equipped with the standard 7G-TRONIC PLUS automatic transmission (a six-speed manual transmission will follow in the second quarter of next year), the diesel SLK can cover the sprint from zero to 100km/h in 6.7 seconds and achieve a top speed of 243 km/h. Moreover, the flexibility of the SLK 250 CDI is nothing short of phenomenal. Thanks to its enormous diesel torque it accelerates from 80 to 120 km/h in just 4.3 seconds – easily the best figure in this class, making for safe and effortless overtaking.

Apart from all this, the SLK 250 CDI is the most economical and therefore the most environmentally compatible roadster in its segment. It is happy with 4.9 litres of diesel fuel per 100 kilometres (NEDC combined consumption), which corresponds to CO2 emissions of 128 g/km. In other words, the diesel SLK combines thoroughbred sports car performance with the fuel economy of a sub-compact. This guarantees effortlessly superior driving pleasure with great fuel efficiency.

The diesel engine achieves its exemplary output, torque, fuel consumption and emissions figures, as well as its highly impressive smoothness for a diesel unit, thanks to a series of innovative technologies. These include fourth-generation common-rail injection with precise injection timing, as well as two-stage turbocharging. Like all SLK models, the SLK 250 CDI is fitted as standard with an ECO start/stop system.

The frugal fuel consumption makes the SLK 250 CDI a car with superior long-distance qualities. Using the European motorways, it is quite possible to drive non-stop from the North Sea all the way to a beach on the Mediterranean. Very comfortable sports seats, a comfortable suspension setup and the largest luggage capacity in this segment also do their bit to create the right conditions.

As it shares the same genes with the other members of the successful SLK family, the SLK 250 CDI combines lightfooted sportiness with stylish comfort, a striking sports car design and absolute suitability for day-to-day use, while also delivering top performance with exemplary ecology. This means that the diesel version, too, provides open-top driving enjoyment at an extraordinarily high level.

Likewise, the SLK 250 CDI too is available with a choice of three versions of the famous vario-roof – one of them the panoramic vario-roof with MAGIC SKY CONTROL. This glass roof can be changed from light to dark at the touch of a button. There are also three suspension variants: a conventional steel suspension, a sports suspension with a stiffer spring and damper setup and a suspension with an electronically controlled, fully automatic damping system.

Externally the new SLK 250 CDI is no different in appearance from the petrol models. It even retains the twin exhaust system, and therefore has the same stunning looks for which all the SLK models are known.

The SLK 250 CDI demonstrates just how much Mercedes-Benz has achieved with the diesel engine. A comparison of the world’s very first diesel saloon, the Mercedes-Benz 260 D of 1936, with the new diesel Roadster, reveals some astounding developments. The 260 D needed 0.3 litres of fuel per kilowatt per 100 kilometres, whereas the SLK 250 CDI requires a mere 0.03 litres – a bare tenth of the amount. We see the same picture in terms of the power-to-swept-volume ratio: the forefather of all diesel cars, the 260 D, generated 17.7 hp from one litre of displacement, while its family’s latest offspring, the SLK 250 CDI, produces 95.1 hp – more than five times the figure. The SLK 250 CDI thus shows that the diesel engine still holds remarkable potential for the future.

Mercedes-Benz diesel engines will now benefit from twin‑wire arc spraying technology that has been used exclusively in AMG engines for the last five years. NANOSLIDE technology, developed by Mercedes-Benz,is the process in which twin-wire arc spraying is used to melt iron/carbon wires and spray them onto the cylinder surfaces of the lightweight aluminium crankcase with the help of a gasflow. Very fine finishing of the resulting nano-crystalline iron coating creates an almost mirror-like, smooth surface with fine pores, which reduces friction and wear between the piston assembly and the cylinder wall. Other advantages include lower engine weight, less fuel consumption and lower emissions. This innovation from Mercedes-Benz has been successfully used in the 6.3-litre AMG engines since 2006.

Mercedes-Benz uses the collective term BlueEFFICIENCY to describe a whole range of different measures designed to reduce fuel consumption and emissions: sophisticated aerodynamics, weight-saving measures and intelligent control of ancillary units are a few examples. With NANOSLIDE technology, the world’s oldest automobile manufacturer is adding another innovation to this technology package. It sets new standards in the production of cylinder linings. These help to ensure that the piston moves up and down within the cylinder with the least possible friction losses. Comparatively heavy grey cast-iron liners with a thickness of up to five millimetres are the current state of the art.

The NANOSLIDE procedure takes a new approach. Wires of iron/carbon alloy are melted in an electric arc, and the melted material is “sprayed” onto the cylinder wall by a gasflow, where it is deposited as a layered, ultra-fine to nano-crystalline coating. The NANOSLIDE coating is then given an extremely smooth finish by a special honing process, after which it has a thickness of only 0.1 to 0.15 millimetres and has a mirror-like surface. The honing process also exposes pores in the material which are able to retain oil and thereby ensure optimal lubrication of the piston assembly. The result is not only low friction, and therefore greatly reduced mechanical friction losses compared to grey cast-iron cylinder liners (up to 50 percent), but also extremely high wear resistance.

Mercedes-Benz has plenty of experience with its in-house development of NANOSLIDE technology. In July 2005 Mercedes-AMG GmbH presented a 6.3‑litre V8 which not only delivered outstanding performance figures, but was also the world’s first series production engine to feature cylinder walls with a twin-wire arc sprayed coating. Since 2006 this cutting-edge cylinder coating technology has been a key component of all 6.3-litre AMG engines. The procedure has proved highly successful in more than 75,000 high-performance AMG engines to date, and meets all expectations. The specialist term “NANOSLIDE” has meanwhile become an accolade. The process involves numerous new inventions and ideas, and is protected by more than 90 patent families and over 40 patents.

In view of this positive experience, Mercedes-Benz is the world’s first manufacturer to have developed this technology further for use in a V6 diesel engine.

NANOSLIDE reduces the engine weight by 4.3 kilograms (9.5 pounds) compared to the preceding engine, and brings an additional fuel saving of 3 percent. The V6 diesel engine in the ML 350 BlueTEC, for example, develops an output of 190 kW (258 hp) from a displacement of 2987 cc, and generates 620 Nm of torque. Thanks to BlueTEC with AdBlue exhaust treatment, this M-Class model already meets the emission values planned for 2014 in accordance with the Euro-6 standard, and as such is one of the world’s cleanest diesel vehicles. With a combined consumption of 6.8 litres of diesel per 100 kilometres, the ML 350 BlueTEC improves on the figures of its predecessor by 2.1 litres, or 24 percent. CO2 emissions have dropped from 235 to 179 grams per kilometre, not least thanks to the new NANOSLIDE technology.

The Mercedes-Benz 260 D in the W 138 series was the world’s first series-production diesel passenger car. Seventyfive years ago in February 1936, 50 years after the invention of the petrol-powered automobile by Carl Benz, Mercedes-Benz presented this revolutionary vehicle at the International Motorcycle and Automobile Exhibition in Berlin.

Its 2.6-litre OM 138 four-cylinder engine with the Mercedes-Benz pre-chamber system and a Bosch injection pump produced 33 kW (45 hp) at 3200 rpm, and was installed in the chassis of the petrol-powered Mercedes-Benz 200 with a long wheelbase. The Bosch Four-plunger injection pump allowed engine speeds of up to 3000 rpm and ensured rapid fuel delivery.

Two years prior, in November 1934, after experimenting with various diesel engines in Mercedes-Benz passenger cars, the engineers opted for a modified version of the well-proven six-cylinder in-line engine from the commercial vehicle sector. The result was a four-cylinder unit with a displacement of 2.6 litres (bore x stroke 90 x 100 millimetres). The new engine adopted the truck engine’s smooth pre-chamber combustion process. The technical specifications included overhead valves and a five-bearing crankshaft.

Series production of the model 260 D commenced at the end of 1935, and the world’s first regular production diesel car was premiered in February 1936, at the International Motorcycle and Automobile Exhibition in Berlin. At an average diesel fuel consumption of 9.5 litres, a tank filling was initially sufficient for 400 kilometres, and this increased to no less than 500 kilometres or more after a model upgrade in 1937. This was not without significance considering the relative scarcity of filling stations at the time.

Even in 1936 the diesel engine in the model 260 D delivered impressive fuel economy: average consumption was slightly above 9 litres of diesel per 100 kilometres, considerably bettering the 13 litres consumed by the petrol-powered model 200. Moreover, diesel fuel cost only 17 Pfennigs per litre for holders of a passenger transport licence in 1936: at the time that was less than half the normal cost of petrol. Taxi-drivers in particular immediately opted for this car, which was available in a spacious Pullman version with six seats right from the start.

In September 1936 Mercedes-Benz also introduced a Pullman saloon, a 4/5-seater saloon and the 4/5-seater Convertible B as further body variants of the model 260 D. Apart from taxi-drivers, more and more private customers also chose this very economical vehicle.

As early as 1937 Mercedes-Benz presented an improved version of the model 260 D: the facelifted version now had a modified radiator grille. The slightly smaller headlamps had more curved housings whose bases were inserted directly into the wings. Previously the headlamps had been mounted on a chrome-plated rail in front of the radiator, which was now omitted. The two 6/7-seater model variants were also given redesigned bodies which were both more spacious and more prestigious-looking than the first Pullman versions. New bumpers replacing the dainty versions of the first two years were introduced in 1938.

Modifications to the 260 D for the model upgrade included a wider track at the front (1370 instead of 1340 millimetres) and rear (1390 instead of 1380 millimetres) and a larger fuel tank (50 litres instead of 38 litres), which was now also moved from the engine compartment to the rear of the vehicle.

In February 1938 the previous overdrive transmission was replaced by a fully synchronised four-speed transmission with a direct-ratio fourth gear. At the same time the 260 D – like the model 230 – was given wider wheels and tyres in the interests of standardisation, as well as dual-action hydraulic shock absorbers at the rear. And from early 1938, electrically heated glow plugs made starting easier when the engine was cold.

From 1936 to 1940 Mercedes-Benz produced 1967 examples of the model 260 D. Especially as a taxi, the world’s first diesel passenger car proved to be an absolute long-distance champion: taxi cabs based on the 260 D were still on the road in large numbers well into the 1950s. Mercedes-Benz also used the OM 138 engine, which underwent only very few modifications during the four-year production period of the model 260 D, for other applications. The same engine also powered the L 1100 to L 1500-series vans built in Stuttgart and Mannheim.

Since the sensational premiere of the model 260 D, Mercedes-Benz passenger cars with diesel engines have continuously set new technical standards. After the Second World War, the model 170 D (W 136) was the first newly designed diesel car offered by Mercedes-Benz. It was powered by the OM 636 1.7-litre four-cylinder engine and presented in 1949.

Since then, Mercedes-Benz passenger cars with diesel engines have been a dynamic success story with numerous highlights. These range from the first diesel car with a five-cylinder engine (model 240 D 3.0 in the W 115 series of 1974) to the introduction of CDI technology with common-rail injection in the C 220 CDI of 1997 and BlueTEC emissions control in the E 320 BlueTEC for the American market in 2006, and right up to the development of diesel-hybrid vehicles such as the E 300 BlueTEC HYBRID for model year 2011. The brand is therefore making a decisive contribution towards establishing the diesel engine as an economical, powerful and refined passenger car drive unit with great future potential.