BMW 520d 2015 Review - International

After its global debut in the X3 in April this year, the new 2.0-litre turbo-diesel engine was turned sideways to sit inside the new MINI hatch and the 2 Series Active Tourer, though this is the first time it's found a home in a traditional BMW front-engined, rear-drive passenger car.

It based it around the firm's now-standard process of developing and fine-tuning an ideal single-cylinder concept (at almost 500cc) and then turning it into a modular production reality, meaning the next all-new six-cylinder diesel will look like this, too, plus 50 per cent.

It's a short-stroke design with a 90mm bore and a stroke of just 84mm and besides its obvious east-west and north-south versions, it can also operate with all-wheel drive (and Europe has a 520d xDrive at its disposal, though it's considered utterly unnecessary in Australia).

There's enough power, with 140kW on offer at 4000rpm, but the real story is the torque. The 520d delivers 400Nm of the stuff (up 20Nm on its predecessor) from just 1750rpm.

Compared to modern diesel norms, it's a fairly peaky torque curve, though, with the taper beginning at 2250rpm, but BMW has given the powertrain eight gears to try to ensure there's plenty on tap whenever it's needed. Oddly, the ZF-sourced eight-speed automatic adds an astonishing 75kg on top of the Eurocentric six-speed manual 520d. In most cars, the hydraulic auto adds only between 20kg and 30kg.

One odd spot is that alongside the 520d in Europe is a 518d (the thought of which hasn't exactly sent BMW Australia's product planners into gleeful paroxysms) and it's 30kW and 40Nm down on the 520d, though the hardware is mostly identical.

It's 5kg lighter than the 520d (body for body) but nearly two seconds slower to 100km/h and its top speed is 17km/h down on the 520d auto's 233km/h. You'd bet your house that the 518d delivers some sort of cracking fuel economy as a counterweight to the speed shortfall, but it doesn't. The auto is actually a touch worse!

BMW has pulled a swiftie here, giving the 520d precisely the same gearing as the 518d, but a far taller (3.077 to 3.231) final drive ratio and then relying on the more expensive model's extra torque to cancel out the inherent acceleration shortfall.

The “smaller” engine is a lesser thing in other ways, too, with less vibration damping leading to some added harshness when the idle stop-start does either half of its name. That's not an issue you even notice on the 520d, though.

The work involved in making it a smoother, faster, more economical engine has centred on reducing friction and lifting the fuel-injection pressures.

The common-rail unit now delivers diesel at 2000 bar (up from 1800), which allowed BMW to use new Bosch fuel injectors with seven holes each and up to seven injections per bang. That gives the car a more complete and cleaner burn and that's further enhanced by a new Honeywell variable geometry turbocharger, complete with a ball-bearing interface that BMW claims reduces cold-start friction by up to 50 per cent, or around 20 per cent in normal running.

A new electrically controlled oil pump also reduces friction by delivering the right pressure and volume at the right time.

The pistons are new, the bedplate is new, the block is largely new, the combustion system is new, the cooling circuit is new and the balancing system is new. So, newish, then.

Also new is the three-layer damping blanket that surrounds the engine (and also helps it to warm up faster) and it works a treat.

The increasing efficiency of direct-injection turbo petrol motors can make you wonder whether there's a real future for diesels, but the BMW engine pushes back against those thoughts pretty hard.

The 520d does its level best to feel like a petrol engine on the road and its start-stop performance is, initially, enormously impressive. There's no heavy clunking or wobbling. It just stops and then it restarts. Simple and smooth as that...

It does more of it as it drives off, with a slight torque hole beneath 1500rpm soon dispatched to memory as it bursts away as soon as the turbo begins to spin. For all the weight it's carrying, it's a strong accelerative surge, too, with the slick auto keeping it in the narrow torque band so smoothly you barely know it's there.

You barely know the thing's a diesel either (at least, mostly). A part of the reason for that is that seventh and eighth gears are overdriven (eighth by a long, long way -- 0.640:1), so the revs are lower than most cars at the same speed. It pulls around 1800rpm at 130km/h, for example, and that helps to keep the cabin quiet.

There are petrol engines out there that feel worse than this and while it tapers away quickly after the power peak, the auto makes sure you're never caught without urge. It's at its best stroked along with the throttle flexed when it's needed and then it delivers strong mid-range urge without a payment in coarseness.

The response is sharper and more urgent in its Sport and Sport+ modes and the 520d also has Comfort and Comfort+ modes to wander through before you get to the EcoPro mode (which you'll need to be in to obtain its best fuel economy figures).

The steering is a bit woollen and ordinary in both comfort modes (Comfort is the default mode), but the sport modes lock out the tallest of the gears. Still, it will step down four gears if you push the throttle through its kickdown, regardless of the mode you're in.

But you'll want to drive it in Sport most of the time, because that's where the 520d feels the most, well, BMW. It's quicker to change gear, the steering feels faster and more intuitive and the entire chassis perks up like it's 200kg lighter.

There are downsides, though. Even though the 5 Series scored a facelift last year, parts of the interior are feeling old -- especially in the era of the new C-Class. And, frankly, pieces of the leather trim didn't seem to have the finish and precision we expect from BMW.

But it's a good, solid performer and the addition of this engine has made it better in every way. In its market, you'd want to have a pretty good reason for going for another option and we can't think of too many.