What is it?
A BMW 6-series that very few people will buy, though lots of people ought to; a genuinely powerful diesel convertible with impressive economy, excellent refinement, and a great deal else to recommend it.
BMW has slotted the stonking twin-turbo 3.0-litre straight six from the 3-series and 5-series into its boulevard-cruising 6-series Convertible. Even though the engine provides over 280bhp, BMW claims 40.9mpg, so 600 miles between fill-ups should be possible.
What’s it like?
Pretty much the perfect long-distance open-top GT – as long as you don’t mind the looks. The huge surge of torque (428lb ft at 1750rpm) wafts the 635d along with ease and the six-cylinder diesel has got to be one of the most sonorous oil-burners around.
The rest – apart from a few mild mid-life cosmetic tweaks – is standard 6-series fayre. That means solid, secure handling, but not much in the way of sporting agility.
Should I buy one?
If you like the looks and the idea of a 6-series and you pay for your own fuel, yes, without question. However, the Coupe version, which is over £5k cheaper, will probably be the bigger seller. That's because many image-conscious 6-series convertible buyers will automatically be put off by the idea of a diesel engine, no matter how good it is or how much sense it makes.