Huge pulling power all of the time. That’s the defining characteristic of the potent E420 CDi – the first car to receive Mercedes’ new 4.0-litre V8 diesel. A development of the earlier V8, the engine gets third-generation common-rail injection and a new electronically controlled twin-turbocharger system.The result? Even quieter running, a smoother power delivery and effortless high-speed performance.The E420 CDi produces a sturdy 310bhp at 3600rpm, 63bhp more than the old engine. As for torque, the new unit offers up a staggering 538lb ft at 2200rpm, 125lb ft more than before, and 428lb ft from just 1600rpm.Turn the key and there’s a faint trace of mechanical chatter, although it is extremely well isolated. On light throttle openings the engine is near silent, making for serene cruising. The real action comes when you nail the throttle and the Merc gathers itself up before lunging forward in one linear surge all the way up to the 5000rpm cut-out.Against the stopwatch, the E420 CDi hits 62mph in just 6.1sec. Top speed is limited to 155mph, though it would hit 180mph without electronic intervention.The attraction continues with a highly respectable 30.4mpg on the combined cycle, providing a range of over 460 miles between refills. Even so, the new engine weighs a massive 260kg and the car feels nose heavy and less nimble than other E-class models through corners.Although not planned for sale in the UK, with sufficient interest Mercedes would consider bringing the E420 CDi here. That day can’t come soon enough.