Punchy, refined and ever so frugal, BMW’s latest diesel engine provides the 520d with a new lease of life

What is it?

A slightly faster, more economical and further refined version of one of the UK’s best-selling executive class estates – the BMW 520d Touring.

Having undergone a mid-life facelift last year with a number of mild exterior and interior styling tweaks, Munich’s popular mid-range model has now received a new four-cylinder diesel engine in a move that further enhances its standing against rivals including the newly facelifted Audi A6 2.0 TDI, Jaguar XF 2.2D and Mercedes-Benz E220 Bluetec.

The B48-designated unit is the same longitudinally mounted 2.0-litre common rail unit unveiled in the facelifted X3 xDrive20d back in April. In the 520d, it delivers 187bhp at 4000rpm and 295lb ft of torque on a band of revs between 1750 and 2500rpm.

This gives it a slight 6bhp and 15lb ft increase over the old N47 engine, with which the 520d’s new engine shares its 90.0mm bore and 84.0mm stroke measurements. Despite the apparent similarities, though, BMW claims the B48 is new from the ground up.

Key among its developments is a new Bosch injection system. It operates at a higher pressure than previous incarnations, reaching peak values of up to 2000bar or some 200bar higher than before. It also receives injector nozzles with seven holes for improved combustion properties.

The new BMW engine also adopts a new variable geometry Honeywell turbocharger that is claimed to bring a 50 per cent reduction in frictional losses due to new bearings. There is also a more efficient electrically operated oil pump that brings reduced pumping losses compared with the older N47 engine.

As before, buyers can mate the 520d’s new engine to a standard six-speed manual or optional eight speed automatic gearbox – the latter running a heavily over driven 0.64:1 top gear in combination with a 3.1:1 final drive ratio and a range of fuel saving features that underpin BMW’s EffientDyanmics initiative.

Alongside standard rear-wheel drive, BMW also offers the 520d with optional xDrive four-wheel drive. Beware, though. Despite its traction enhancing qualities, it adds 105kg to 1735kg kerb weight of the standard rear-wheel drive 520d Touring driven here, taking it to 1840kg.

For those on a tighter budget, BMW has also launched a reworked version of the 518d in both saloon and Touring bodystyles. It receives a slightly detuned version of the B47 engine with 148bhp at 4000rp and 265lb ft between 1750 and 2500rpm.  

What's it like?

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.

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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.

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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?

Should I buy one?

Along with the charms of its new engine, the 520d is also an engaging drive when set up in Sport Plus mode – where its instruments alter from a cool shade of white to a glaring shade of red.

If you’re in the market for an executive class car or are looking at securing a new company car you’d be mad not to give it consideration. As far as every day motoring goes, it is about as much as you’ll ever need, not least in Touring guise. 

BMW 520d Touring automatic

Price £35,840; Top speed over 140mph; 0-62mph under 8.0sec; Economy 62.8mpg; CO2 118g/km; Kerb weight 1735kg; Engine 4-cyls, 1995cc, turbocharged, diesel; Power 187bhp at 4000rpm; Torque 295lb ft at 1750-2500rpm; Gearbox 8-speed automatic

Add a comment…
wlkon20 18 September 2014

It's the B47

Good review, but your designation of the engine code alternates inconsistently between B47 and B48. The correct designation is B47. If I'm not mistaken, construction material of the engines differ - B47 is aluminium-built, not sure about the N47. Correct me if I'm wrong?
bomb 17 September 2014

Got to agree with Will86...

...on this one. Sure, with sufficient money we'd all love the large engine but I think we all need to recalibrate a little and realise the amount of performance and economy available from just a 2.0 these days. Yes, you don't a great noise but these things really shift.
Will86 17 September 2014

What's the problem with a 4 pot?

Sure it might be nice to have a six cylinder but with all the costs of running a car, a four cylinder engine allows you to enjoy the qualities of a car like the 5 series without it costing an arm and a leg. As for performance, all that torque will allow effortless pace (it certainly does in the 320d) and to put it in perspective, the original 530d had 184bhp and 290lb/ft. So the only real issue with a 4 pot is the noise, but as refinement appears improved with the new engine, the case for the six cylinder is dwindling.