All five of the engines available for the two iconic designs feature state-of-the-art technology. All are thus compliant with the Euro 6 standard.

The BlueTEC diesel engines for the CLS-Class are environmentally friendly but powerful. Developed by Mercedes-Benz, BlueTEC is a modular concept that effectively reduces emission levels from diesel vehicles. The CLS-Class BlueTEC models are equipped with an oxidising catalytic converter and particulate filter, as well as an exceptionally durable NOx storage-type catalytic converter. These are combined with an additional SCR (Selective Catalytic Reduction) converter. SCR exhaust gas aftertreatment converts nitrogen oxides into harmless nitrogen and water vapour, thereby keeping untreated emissions to a minimum.

The new entry-level model is the four-cylinder diesel engine in the CLS 220 BlueTEC featuring fourth-generation common rail direct injection, two-stage turbocharging and BlueTEC technology. It generates 125 kW (170 PS) with maximum torque of 400 Nm. Acceleration from 0 to 100 km/h takes 8.3 seconds (Shooting Brake 8.6 seconds); the top speed is 226 km/h (Shooting Brake 220 km/h) and it consumes 4.6 litres of diesel (Shooting Brake 4.9 litres) over 100 kilometres (NEDC combined). This corresponds to CO₂ emissions of 122 (127) grams per kilometre. The same engine appears in the CLS 250 BlueTEC and CLS 250 BlueTEC 4MATIC, as well as in the equivalent Shooting Brake variants. In this version it delivers 150 kW (204 hp) and creates 500 Nm of torque to spin the crankshaft.

The most powerful diesel engine within the CLS-Class is the V6 in the CLS 350 BlueTEC and CLS 350 BlueTEC Shooting Brake. It produces 190 kW (258 hp) of power (CLS BlueTEC 4MATIC – 185 kW (252 hp)) and supplies torque of 620 Nm.

(Figures in brackets: CLS Shooting Brake)
 

A new six-cylinder petrol engine celebrates its début in both models. Key benefits include turbocharging, stratified charge operation and a 3.5-litre displacement. Unlike the familiar V6 biturbo with three-litre displacement, the new engine operates in either stratified or homogeneous mode depending on the operating conditions. It thus continues to deploy what is known as stratified combustion as launched with the 3.5-litre V6 naturally aspirated engine in 2011. With stratified charge operation there is significant excess air. To this end, the fuel is not injected into the air until the compression phase, after the air has been compressed by the pistons. A precision-controlled electronic multiple injection process ensures that a fuel-air cloud localised in the area of the spark plug forms only at the time of ignition. The spark plug lights the ignitable fuel/air mixture around it, while only a very lean mixture with a high proportion of excess air is to be found in the remainder of the combustion chamber. This enables extremely efficient combustion. Gas cycle losses are reduced considerably because adjustment to the operational load takes place largely without the intake air throttle.

Compared to the previous naturally aspirated engine in the CLS 350, the new six-cylinder engine produces 20 kW more output at 245 kW (333 hp). Its torque increases by 110 Nm to 480 Nm and is available in the wide engine speed range from 1200 to 4000 rpm. Thanks to its output potential and extremely high torque at lower engine speeds than the three-litre V6 biturbo, the new stratified charge engine provides the ideal conditions for sporty, agile driving pleasure and a high level of refinement combined with high efficiency.

The V8 petrol engine in the CLS-Class hits its power peak at 300 kW (408 hp) and up to 600 Nm of torque.

(Figures in brackets: CLS Shooting Brake)