Update: Click here for official BMW 6-series facelift details.

BMW will be adding its twin-turbo 3.0L diesel engine to both the 6-series coupe and convertible, with the new car set to wear 635d badges. The output of the 286hp six-cylinder motor will enable the big coupe to reach 100km/h from rest in around 6 seconds, all the way to an electronically controlled speed limit of 250km/h.

The rationale behind the 635d is a strange one. Why would buyers after luxurious sporting coupes go for an economic diesel motor? Further, the release of the new diesel 6 will coincide with the launch of a new 163hp diesel version of the 3-series convertible, being offered initially in 320cd guise.

BMW’s 3.0L diesel is one of the best engines of its kind in the world, but many purists agree that a diesel engine does not belong in a coupe. However, given the performance numbers, does it really matter? Still it’s unlikely that the diesel 6-series will be for sale in the US.