With the efficiency advances made by four-cylinder direct injection petrol engines, the venerable common rail diesel has come under increasing sales pressure of late. But in the case of the 5-series it is the four-cylinder oilburner that continues to rule the roost, accounting for up to 20 per cent of sales on a global basis.
In its latest incarnation, BMW’s four-cylinder diesel engine proves highly convincing, providing the 520d with a broad spread of performance, outstanding efficiency and improved refinement.
The adoption of a new injection process and alterations to the induction process sees the B47 deliver more instantaneous response and even greater mid-range flexibility than the old N47 engine.
It is only low down in the range that the new 2.0-litre unit struggles with its relative lack of capacity, offering acceptable but far from strapping qualities below 1500rpm. From there onwards there is strong urge until the efforts of the engine begin to tail off beyond 4500rpm.
Perhaps more than the additional power and torque, it is the improvement in cold start and on-boost refinement that really marks the 520d’s engine out.
With improved frictional qualities and additional sound deadening material in the form of a plastic jacket that nestles around the new engine to dampen mechanical noise, it offers truly hushed qualities at typical motorway speeds. It is only when you explore the upper reaches of the rev range that you begin to register any traditional diesel like acoustics – and even then it is hardly loud.
The ultra-precise shift action of the optional eight-speed automatic gearbox, as fitted to our test car, adds to the impression of outstanding refinement, providing crisp and intuitive shifting in any situation.
In kick down mode, it will drop up to four gears to provide the 520d Touring with convincing vigour on the run. A heavily over driven 0.64:1 eighth gear ratio and 3.08:1 final drive also endows it with a wonderful loping gait at typical motorway speeds thanks to the strong levels of torque.
In saloon guise, the new 520d is claimed to hit 62mph in 7.7sec and reach a top speed of 145mph. But with an added 135kg, the Touring requires just less than 8.0sec and runs to 140mph. However, it is at the pumps where the new BMW really impresses.
Official economy claims give the 520d saloon a combined 69.0mpg and average CO2 emissions of just 109g/km in combination with standard 17-inch wheels and 225/55 R17 tyres. The 520d Touring can’t quite match it, but its 62.8mpg and 118g/km is still very impressive, endowing it with a theoretical range of 967 miles on the car’s standard 70 litre fuel tank.
Criticisms? The interior of the sixth-generation 5-series is beginning to show signs of age with some less than dazzling materials and a clutter of buttons spread across the dashboard.
The optional adaptive damping control system is also unnecessarily complex, offering five different modes: Sport Plus, Sport, Comfort, Comfort Plus and Eco Pro. Choice is good but one has to ask: do you really need such finite adjustment?