The 2012 Mercedes-Benz S350 BlueTec diesel-powered sedan is the latest S-Class entry in the U.S., a lineup that currently starts with the S400 Hybrid ($91,000) and also includes a V-8 (the S550, $93,000) and a V-12 (the S600, $158,050).  It’s also the most economical S-Class when it comes to fuel usage and, more importantly, it can go over 737 miles (1186 km) between fill-ups.  Of course, Mercedes-Benz has the American luxury diesel sedan market all to itself: at the present time, BMW doesn’t import the 730d or 735d, Audi doesn’t import any of the A8 TDIs, and Jaguar doesn’t import the XJ diesel.

The current version of the S-Class has been on sale since 2006 (as a 2007 model) and it was refreshed in 2010, getting a new bumper and grille, LED taillights and daytime running lights, and an integrated exhaust at the rear.

The S350 BlueTec is the automaker’s first S-Class diesel in the United States since the 1995 model year and it’s powered by a powerful V-6 diesel engine that develops 240 horsepower and 455 pound-feet of torque, bringing the oil burner S-Class from 0 to 60 mph in seven seconds.  (This is the same engine that is found in the new 2012 ML350 BlueTec.) The S350 BlueTec comes with Mercedes’ 4Matic all-wheel drive technology standard.

The new V-6 is designed to minimize diesel exhaust emissions through the use of several technologies including a four-valve-per-cylinder engine that features centrally located piezo-electric injectors, CDI direct injection, a variable-nozzle turbocharger, and exhaust gas recirculation.

But that’s not all.  The S350 BlueTec also treats the exhaust stream with an oxidizing catalytic converter, a (maintenance-free) particulate filter, an SCR converter, and a NOx storage converter.  In the “denox” storage converter, nitrogen oxides are temporarily absorbed and then released during brief regeneration pulses of a richer fuel-air mixture.  They then react with other exhaust gas to form nitrogen, which is harmless.  The regeneration pulses also raise temperature inside the particulate filter, which then in turn burns off the deposits.

A new seven-speed transmission features an advanced torque converter lock-up clutch that provides better fuel economy and quieter operation while being more responsive to the driver’s input.  It uses FE-ATF, a new low-viscosity transmission fluid that is blue instead of red.  The FE-ATF, along with new planetary gears, bearings, and internal seals, provides less friction and improves fuel economy.

The diesel S-Class’ fuel economy is by far the most impressive in the S-Class range with 20 mpg (11.76 l/100 km) in the city and 31 mpg (7.58 l/100 km) on the highway.  Even compared to the S400 Hybrid, which has the same EPA highway fuel economy rating as the S550 (25 mpg or 9.4 l/100 km) but got 22% better fuel economy in the city (19 mpg or 12.37 l/100 km compared to 15 mpg or 15.68 l/100 km), the diesel’s almost 20% superiority in highway fuel economy over both models gives it a range of 737 miles (1180 km), which is unparalleled range in its class.

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