Car and Driver: Mercedes-Benz Debuts New Four-Cylinder Diesel

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In Woody Allen’s 1973 sci-fi send-up Sleeper, his character finds a 200-year-old Volkswagen Beetle in a cave and starts the engine, which turns over without the slightest hesitation. Allen could have substituted a W115 Mercedes 200D in the same ridiculous but truth-based scene. Mercedes diesels, like air-cooled VW flat-fours, are pretty much indestructible. Now, Mercedes has released a new-generation of its venerable four-cylinder diesel.

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The latest OM 654 2.0-liter turbodiesel four-cylinder debuts in the Euro-spec 2017 E220d this spring, and sometime later in the U.S. (with a higher numeral, due to our hubris over engine size). It replaces the OM 651 2.1-liter diesel in service worldwide since 2008, although our time with it was considerably shorter; it arrived here in 2013, first in the GLK250, and then in the E250 and ML250 BlueTec models. Of that engine’s three strengths offered in Europe (250, 220, and 200), we received only the most powerful.

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The new engine—in 220 strength at least—makes 195 horsepower at 3800 rpm (up 25 hp) and 295 lb-ft of torque between 1600 and 2400 rpm. Compared to our current 2.1-liter engine, it achieves the same horsepower but nowhere near the 369 lb-ft that made our 2014 E250 sedan sneaky fast. Mercedes hasn’t confirmed U.S. specifications yet, but we’ll bet our version will produce more torque.

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More so than output, the big news is the OM 654’s cast aluminum block, as Mercedes is waving goodbye to the trusty cast iron block for four-cylinder diesels. This helps the new engine save a claimed 101 pounds (with all mounted accessories) versus the OM 651 220-spec diesel. Mercedes also used aluminum for the crankcase, reduced cylinder spacing by 0.16 inch, removed the second series turbocharger in favor of a single setup, and switched to plastic engine mounts, which reduce both weight and vibration. Each of the cylinders displaces 0.5 liters—all the major German automakers believe this volume provides max power and efficiency—and is lined with slippery Nanoslide, an iron-carbon coating on the cylinder walls that cuts friction.

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For the pistons, Mercedes engineers chose steel instead of aluminum, leveraging the hard metal’s lower heat conductivity to improve combustion at higher temperatures and reduce friction between 40 and 50 percent. This is possible since aluminum, when hot, expands at a higher rate than steel, so the more tightly controlled tolerance between the steel piston and the aluminum cylinder wall becomes especially advantageous, according to Mercedes.

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In the wake of the VW TDI scandal, we can’t talk about a diesel engine without bringing up exhaust emissions. Here, Mercedes installed all of the after-treatment components within the engine compartment. Instead of particulate filters and a trunk-mounted urea tank located downstream, these parts are installed on the engine itself. Even both catalytic converters—one for oxidation, the other a selective catalyst reduction (SCR) that reduces nitrogen oxides—are mounted as close to the engine as possible so that it won’t require the lengthy cold-start warmup procedures that have gotten VW into more trouble with the feds. This should also make it easier to install diesel powertrains across multiple vehicles.

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• 2017 Mercedes-Benz E-class: All In the Family-
• Why 0.5-Liter Cylinders Will Soon Dominate Automotive-Engine Design-
• Global Cooling: Mercedes to Debut Air Conditioning with CO2 Refrigerant-

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We don’t yet know how efficient the new engine is, or when it’ll appear in the new E-, GLC-, and GLE-class models. The brawnier 3.0-liter turbodiesel V-6 currently in the full-size GLS350d isn’t going away. And thankfully, neither is Benz’s commitment to any of these hardy, longlasting oil-burning engines.

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