Europe's Mercedes-Benz S 320 CDI BlueEfficiency began this year as the most frugal S-Class available. With 235 horsepower and 398 pound-feet of torque, 31 mpg, and S-Class luxury, it's a fine runner if you want to have it all without grenading your treehugging credentials. But hang on – new reports are now popping up suggesting that Mercedes will soon up the frugal luxury stakes with a new S 250 CDI BlueEfficiency – the first S-Class with a four-cylinder engine.

According to the rumors, it will use the 2.2-liter, twin-turbocharged diesel four-pot fitted to the E- and C-Class, putting out 224 horsepower and 368 lb-ft of torque. The obvious sacrifice in sheer grunt and top end ought to be made up for by the mileage, which is predicted to be 35 mpg. To keep the four- and six-cylinder engines from being too close to one another, the six is said to grow in output to 285 hp and 516 lb-ft, and that should spell the end of the eight-cylinder S 450 CDI engine.

[Source: Auto Internationaal (translated) via 4WheelsNews]