Of course, the company’s major sales target area, America, is still in the Dark Ages when it comes to appreciating today’s oil-burner technology. But with 40 per cent of cars sold in Europe last year being diesel powered, these days no self-respecting automaker can really afford to not offer a compression ignition motor in its engine line-up, and preferably one of its own making.
For its first in-house diesel motor, Volvo had sensibly applied some practical forethought. When the Swedish company launched its Audi-based in-line five-cylinder petrol engine in 1991 in the 850 saloon (before Volvo was bought by Ford and housed in the Blue Oval’s Premier Automotive Group), its design already allowed for diesel power.
Head and block are cast in aluminium, and despite having to be strong enough to withstand the greater stresses of the oil burning combustion process, the engine tips the scales at a relatively light 185 kg. It is a compact motor, so mounting it transversely in the engine bay presented little engineering challenge, and its slim block frees up space for the integration of safety crumple zones into the car’s frontal body design.
Clearly undersquare (a diesel is inherently low-revving, so a long stroke is not a disadvantage), the swept volume is 2 401 cm3 with separate overhead cams operating the two inlet and two exhaust valves per cylinder, both driven by a single belt that also drives the fuel injector pump. The use of lightweight components and roller-finger cam followers contribute towards reducing internal friction, and a modest 18:1 compression ratio lessens the mechanical load on the engine.
With the S60 D5, Volvo was the first manufacturer to use Bosch’s second-generation common rail injection system. Fast-acting solenoid valves control the amount of fuel and the injection timing, resulting in finely atomised diesel being delivered to the single central vertical injector at pressures up to 1 600 bar. Complicit in the operation is a VNT (variable nozzle turbine) turbocharger, which incorporates movable guide vanes in the input side to provide optimum flow conditions – and hence efficiency – throughout the rev range, enhancing power output and providing a flatter torque curve. And the technology does not end there.
The D5 is the first engine in the world to feature an electronically controlled exhaust gas recirculation (EGR) system that cools the recirculated exhaust gases before mixing them with the intake air, which helps further reduce emissions of nitrogen oxide in particular. Incidentally, the turbo housing is cooled with the engine oil.
What results is Volvo’s most torquey five-pot engine offering (yes, including the high performance turbocharged T5 petrol unit). The 120 kW D5 pumps out 340 N.m from 1 750 to 3 000 r/min, compared with the 184 kW T5’s 330 N.m from 2 400 to 5 200 r/min. Obviously there is a difference in performance, with the oil-burner’s low- to mid-range strength offering much more relaxed, though far from sluggish, progress. Indeed, for a saloon weighing-in at just over 1,5 tons in test trim, a 0-100 km/h time of 9,65 seconds and a top speed of 206 km/h will satisfy most enthusiastic tastes.
That the D5 does it while consuming diesel at an average of around 7,8 litres/100 km merely broadens the appeal. Clever automatically adjustable engine mountings do an excellent job of reducing characteristic vibration, although a zizzle from the overhead console, a slight blurring of vision in the interior mirror, and a faint tingle from the clutch pedal give notice that to eliminate it completely is not easy.
But we are nit-picking: the D5 provides a superbly refined drive, and the distant thrum of the five-pot motor when pushed towards the 4 500 r/min redline has its own appeal. The light but slightly notchy five-speed shifter requires little attention once on the move, as a squeeze on the accelerator is often all that it takes to clear traffic or surmount a hill with little apparent effort. The D5 hardly stumbles at low revs, and – for a manual – does a good job of smoothing the turbo boost effect.
The S60 is a known force on local roads, being premium class, and offering style, comfort, benign road manners (initial steering input is sharp, though), bags of features and all that is best in safety equipment. Sadly, Volvo interiors have lost much of their “Swedishness” since the Ford takeover – one tester noted that it seemed to pamper to American tastes – but you cannot fault the ergonomics of the current design direction.