Any engine that makes a two-tonne luxury conveyance like this capable of accelerating as quickly as a hot hatch, of soothing away miles with the manners of a first-class cabin attendant and of delivering more than 50mpg merits a warm reception from all quarters.
To be fair, the greatness of BMW’s 3.0-litre six-cylinder diesel is so well established that it’s almost beyond question. If any oil-burning engine deserves immunity from the toxic swell of public opinion against diesel, it’s this one.
Whether it will survive that swell or not will have little to do with what’s just, of course. But rest assured, this engine has the muscle and tractability to move a heavy car effortlessly, and its application in the 630d GT has more than enough suaveness and refinement to suit a car with such a luxury-targeted brief.
This engine’s 457lb ft of tractive urge and ZF’s excellent eight-speed automatic gearbox make relaxed ground-covering blissfully easy.
There’s a distant, faintly gravelly thrum audible from it at times, but even at high revs and under high loads, it’s no chore to listen to.
And you can easily ignore it if you prefer: the 67dB of cabin noise we recorded in the 630d GT at a 70mph cruise shaded an Audi Q7 3.0 TDI by 1dB at the same speed and, despite its frameless doors and windows, the BMW seems very well insulated from the outside world when you’re travelling within.
What’s more, although our noise measurements are always done in the front seats for consistency, the 6 Series GT ought to be even quieter for its back-seat passengers because BMW has used extra soundproofing materials inside the rear doors, roof and seat backrests compared with what you’ll find in an equivalent 5 Series.
As well as being refined, the car is made deliciously smooth to drive by a progressive brake pedal feel and superbly linear-feeling accelerator.