This is a comparison test between the most popular diesel versions of the latest BMW 5 Series and of the 2014 Mercedes E Class. The BMW 520d is powered by a 2.0-litre diesel engine that develops 181 bhp and 380 Nm of torque. The BMW 520d is rated with a fuel economy of 62.8mpg and a 119g/km CO2 emissions level. The Mercedes E220 CDI is powered by a 2.1-litre diesel engine that develops 168 bhp and 400Nm of torque. In terms of efficiency, the E220 offers a 57.7mpg fuel consumption and a 129g/km CO2 emissions level.