A new entry-level four-cylinder diesel engine option has been added to the BMW 6 Series GT’s selection of power units, the new model acquiring the 620d badge.

It means that BMW’s slightly taller Mercedes CLS and Audi A7 rival now sports five engine options, while four-cylinder power is available in both petrol and diesel form alongside the more powerful six-cylinder units. Neither the Merc nor the Audi comes with the option of a four-cylinder just yet.

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The 6 Series GT itself is a fairly new addition to the BMW range. Revealed at the Frankfurt Motor Show last year, it's essentially a rebadged version of the 5 GT.

The turbocharged 2.0-litre unit produces 187bhp, with maximum 400Nm of torque available low down in the rev band, between 1,750rpm and 2,500rpm. BMW claims that the new 620d is capable of 0-62mph in 7.9 seconds, while drive is sent to the rear wheels via an eight-speed Steptronic automatic gearbox.

The new member of the 6 Series GT family is the most fuel efficient version on paper. BMW claims 56.7mpg on a combined run, while CO2 emissions are rated at 129g/km.

Despite being the entry-level model, suspension and drive technology available further up the range will make the 620d’s option list, including BMW’s Adaptive Two-Axle Air Suspension and Integral Active Steering. Full UK pricing and a release date will be revealed soon.

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