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.
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.
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.
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.
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.
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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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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