The BMW 6 Series Convertible (F12 LCI), specifically the 640d variant with the Steptronic automatic transmission, represents a compelling blend of performance, luxury, and efficiency within the large convertible grand tourer segment. Produced from 2015 to 2018, this facelifted version of the F12 generation benefited from styling revisions, updated technology, and refined engine options. The 640d, positioned as a mid-to-upper range offering, catered to buyers seeking strong diesel torque and long-distance comfort without sacrificing the prestige associated with the 6 Series badge. It occupied a space between the entry-level 630d and the higher-performance 650i models.
Technical Specifications
| Brand | BMW |
| Model | 6 Series |
| Generation | 6 Series Convertible (F12 LCI, facelift 2015) |
| Type (Engine) | 640d (313 Hp) Steptronic |
| Start of production | 2015 |
| End of production | 2018 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Cabriolet |
| Seats | 4 |
| Doors | 2 |
| Fuel consumption (urban) | 6.2-6.7 l/100 km (37.9 – 35.1 US mpg, 45.6 – 42.2 UK mpg, 16.1 – 14.9 km/l) |
| Fuel consumption (extra urban) | 5.0-5.3 l/100 km (47 – 44.4 US mpg, 56.5 – 53.3 UK mpg, 20 – 18.9 km/l) |
| Fuel consumption (combined) | 5.4-5.8 l/100 km (43.6 – 40.6 US mpg, 52.3 – 48.7 UK mpg, 18.5 – 17.2 km/l) |
| CO2 emissions | 144-153 g/km |
| Fuel Type | Diesel |
| Acceleration 0 – 100 km/h | 5.5 sec |
| Acceleration 0 – 62 mph | 5.5 sec |
| Acceleration 0 – 60 mph | 5.2 sec |
| Maximum speed | 250 km/h (155.34 mph) |
| Emission standard | Euro 6 |
| Weight-to-power ratio | 5.9 kg/Hp, 168.3 Hp/tonne |
| Weight-to-torque ratio | 3 kg/Nm, 338.7 Nm/tonne |
| Power | 313 Hp @ 4400 rpm |
| Power per litre | 104.6 Hp/l |
| Torque | 630 Nm @ 1500-2500 rpm (464.66 lb.-ft. @ 1500-2500 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | N57D30B |
| Engine displacement | 2993 cm3 (182.64 cu. in.) |
| Number of cylinders | 6 |
| Engine configuration | Inline |
| Cylinder Bore | 84 mm (3.31 in.) |
| Piston Stroke | 90 mm (3.54 in.) |
| Compression ratio | 16.5:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Diesel Commonrail |
| Engine aspiration | Twin-power turbo, Intercooler |
| Engine oil capacity | 6.5 l (6.87 US qt | 5.72 UK qt) |
| Coolant | 8 l (8.45 US qt | 7.04 UK qt) |
| Kerb Weight | 1860 kg (4100.6 lbs.) |
| Max. weight | 2365 kg (5213.93 lbs.) |
| Max load | 505 kg (1113.33 lbs.) |
| Trunk (boot) space – minimum | 300 l (10.59 cu. ft.) |
| Trunk (boot) space – maximum | 350 l (12.36 cu. ft.) |
| Fuel tank capacity | 70 l (18.49 US gal | 15.4 UK gal) |
| Length | 4894 mm (192.68 in.) |
| Width | 1894 mm (74.57 in.) |
| Height | 1365 mm (53.74 in.) |
| Wheelbase | 2855 mm (112.4 in.) |
| Front track | 1600 mm (62.99 in.) |
| Rear (Back) track | 1665 mm (65.55 in.) |
| Ride height (ground clearance) | 123 mm (4.84 in.) |
| Drag coefficient (Cd) | 0.29 |
| Minimum turning circle | 11.7 m (38.39 ft.) |
| Drivetrain Architecture | Rear wheel drive |
| Drive wheel | Rear wheel drive |
| Number of gears and type of gearbox | 8 gears, automatic transmission Steptronic |
| Front suspension | Double wishbone |
| Rear suspension | Independent multi-link suspension |
| Front brakes | Disc |
| Rear brakes | Disc |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Steering rack and pinion |
| Power steering | Electric Steering |
| Tires size | 225/55 R17; 245/45 R18; 275/45 R18; 245/40 R19; 275/35 R19; 245/35 R20; 275/30 R20 |
| Wheel rims size | 8J x 17; 8J x 18; 9J x 18; 8.5J x 19; 9J x 19; 8.5J x 20; 9J x 20 |
Powertrain & Engine Architecture
The heart of the 640d is BMW’s N57D30B inline-six diesel engine. This 3.0-liter engine utilizes a sophisticated common-rail direct injection system, delivering fuel at extremely high pressures for optimized combustion. The N57 engine family is renowned for its durability and efficiency. The ‘B’ suffix denotes the latest iteration of the N57, incorporating improvements to the turbocharging system and engine management. Crucially, this engine features a twin-scroll turbocharger, minimizing turbo lag and providing a broad torque curve. The Steptronic 8-speed automatic transmission is a key component, offering smooth and quick shifts. It’s programmed for both comfort and performance, adapting to driving style. The transmission features steering wheel-mounted paddle shifters for manual control, though the automatic mode is generally well-suited to the engine’s characteristics.
Driving Characteristics
The 640d Steptronic delivers a refined and effortless driving experience. The substantial 630 Nm (464 lb-ft) of torque, available from just 1500 rpm, provides strong acceleration in virtually any gear. While not as overtly sporty as the 650i, the 640d offers more than adequate performance for spirited driving, achieving 0-60 mph in around 5.2 seconds. The Steptronic transmission complements the engine well, providing seamless gear changes. The long gearing contributes to excellent highway cruising, while the engine remains remarkably quiet and refined at speed. Compared to the 630d, the 640d offers a noticeable performance upgrade, while remaining more economical than the 650i.
Equipment & Trim Levels
The 640d Convertible typically came well-equipped as standard. Features included leather upholstery, power-adjustable seats with memory function, a premium sound system, automatic climate control, and BMW’s iDrive infotainment system with a central display screen. Optional extras were plentiful, including upgraded leather options, a head-up display, active steering, adaptive cruise control, and a Bang & Olufsen sound system. The convertible top was fully automatic, opening and closing in around 24 seconds. Interior trim options ranged from wood veneers to aluminum accents, allowing for a degree of personalization.
Chassis & Braking
The F12 6 Series Convertible utilized a double-wishbone front suspension and an independent multi-link rear suspension, providing a comfortable yet controlled ride. The suspension was tuned to balance handling and comfort, making it suitable for both long-distance cruising and spirited driving. Brakes were ventilated discs all around, providing ample stopping power. ABS, dynamic stability control (DSC), and traction control were standard safety features. The 640d, due to its weight, generally featured slightly stiffer spring rates compared to the lighter 630d models.
Market Reception & Comparison
The 640d Convertible was generally well-received by automotive critics. It was praised for its refined engine, comfortable ride, and luxurious interior. The fuel economy was a significant selling point, particularly in Europe where diesel engines are more popular. Compared to the 650i, the 640d offered a more sensible balance of performance and running costs. Some critics noted that the steering lacked a bit of feel, but overall, the 640d was considered a highly competent and desirable grand tourer.
Legacy
The N57 engine family, including the N57D30B found in the 640d, has proven to be remarkably reliable. With proper maintenance, these engines can easily exceed 200,000 miles. The Steptronic 8-speed automatic transmission is also known for its durability. On the used car market, the 640d Convertible represents a good value proposition, offering a luxurious and capable grand tourer at a more affordable price point than its petrol-powered siblings. However, potential buyers should be aware of the potential for diesel particulate filter (DPF) issues, particularly if the vehicle has been primarily used for short trips. Regular servicing and preventative maintenance are key to ensuring the long-term reliability of this sophisticated vehicle.
