GoAuto 04/08/2006

WE had better, it seems, get used to it. Turbo-diesel engines are appearing at such a rate in Australia that there is barely a market segment where car-makers are not offering diesel-engined variants.

We had become accustomed to some Europeans, such as Mercedes-Benz and Peugeot, including diesels in their Australian ranges, but now more than just the practical car-makers are getting involved.

We have diesel BMWs, diesel Volkswagens, diesel Alfa Romeos and it seems it won't be long before we have diesel Commodores. What is this? Europe?

Fortunately this headlong rush into oil-burning engines doesn't mean all our cars are about to sound like Kenworth trucks.

In fact the new generation of turbodiesels is so good that, in some cases, it's getting difficult to determine from inside the car just what sort of powerplant is humming away under the bonnet.

A classic example is Jaguar's new S-Type diesel.

Where we in Australia are used to Jaguars with sporting V6 and V8 petrol engines, the Europeans have had familiarity with a turbodiesel S-Type for a while. Reports filtering down from the motoring press over there have been suggesting this is a rather special engine.

As it turns out we know the engine already, because it's also used in the current Land Rover Discovery and Range Rover Sport - where it does a quite impressive job of hauling around a couple of quite weighty, non-aerodynamic 4WDs.

Add another turbo to boost power from the Land Rovers' 140kW to 153kW, then drop the lightweight compacted graphite iron (CGI) - a material claimed to be stronger, stiffer, lighter and more durable than cast iron - 2.7-litre V6 into the almost one tonne lighter S-Type Jaguar and what have you got?

One fast diesel, as it turns out, which also happens to be astonishingly economical for a premium sports saloon even though it produces more torque than the normally aspirated petrol V8.

We'd defy anyone to pick differences between the diesel Jaguar and the V6 petrol version from the passenger's seat once out on the road.

Oil-burning engines as seen in the Mercedes ML-Class - and the Discovery - are getting so quiet with the help of technology (such as the new, super-fast piezo injection systems) that we are approaching the holy grail of the silent diesel.

Approaching. It's still very evident, even when starting up the new Jag diesel first thing in the morning in the enclosed comfort of your garage, that compression-ignition is still far from as quiet as a regular petrol engine.

And there is, despite the existence of hard-working emission control systems including catalytic converters and particulate traps, still a subtle whiff of diesel smell too, although this practically disappears after warm-up.

But of all the turbo-diesels we've driven lately, none have been quite as quiet as the S-Type when cold, and certainly none have been quieter on the move.

And, as we said, the S-Type diesel is also quick off the mark. Partly helped by its standard ZF six-speed automatic, it reaches 100km/h in a smooth, 8.6-second rush.

In fact the figure sounds a little conservative because the S-Type feels quicker than that, delivering a satisfying, deliberate shove in the back when pulling out to pass slower traffic on the freeway. The driver might need to be slightly forceful with the accelerator pedal to achieve this, but the potential for slick accelerative action is always there.

So is the impressive fuel economy.

On the open road, it's not at all hard to get the 227km/h (on unrestricted roads) S-Type as low as 6.7L/100km. Around the city it might creep above the claimed average of 7.8L/100km, but judicious use of the accelerator will keep it close.

In the end, it's quite amazing to be driving a fast Jaguar and filling up at the diesel pump with upwards of 800km showing on the trip meter since the last fill.

You won't get a lot more than that, because the tank is a quite conservative 68 litres and there's a special device which, in order to protect the fuel pump and eliminate the need for priming the system, won't let you completely drain the tank. The S-Type engine will stop when there's four litres of diesel left.

And what about the Jaguar on-road tenacity? Does the turbo-diesel adversely affect the nice, balanced feel of the S-Type?

Not in any noticeable way, largely because of the fact the engine is only 15kg heavier than the petrol V6 and delivers its twin-turbo power so progressively.

The low-inertia turbos, in contrast to regular turbos, are actuated electronically rather than by vacuum, meaning more accurate and efficient control via better management of emissions as well as balanced output from the two cylinder banks.

Like all diesels, there's no exhaust thrum, just a very hushed busy-ness from the engine bay as the speed piles up.

The diesel S-Type's handling shows the same balanced predicability of the petrol versions. There's the "connectedness" that contrasts with the crisper, technical feel experienced in German performance cars. A Jaguar slips on like an old shoe, offering the sense that electronics are less a determinant of what is going on than the driver.

The steering is weighted slightly on the light side, but feels responsive and accurate nonetheless, swinging from lock to lock in a quick 2.75 turns and helping the Jag's combined feelings of stability and agility.

The ride is good too, with nothing fussy like air suspension as used on the bigger XJ models - just a well-sorted balance of springs and shock absorber rates and enough wheel travel to absorb bumps quietly and smoothly.

The S-Type is available with things like active cruise control - to maintain a steady distance from the vehicle in front - and park-distance sensors as well as touch-screen satellite navigation are standard, but you don't get the high-end stuff beginning to appear on German cars.

Head-up display, active steering, swivelling Xenon lights, iDrive-style systems - none of these appear on the S-Type and that's fine.

What you do get is a warm, traditional leather and wood interior with a split-folding rear seat that gives access through a wide portal to a relatively low but quite spacious boot. The traditional Jaguar ambience is very present even if the S-Type shares much of its structure with Ford's US-market Lincoln LS.

Interior space is not class-leading but is quite good nonetheless, with the proviso you don't attempt wearing a top hat in the back. The seat sits high, helping legroom but minimising headroom.

The S-Type's sound system sounds pretty ordinary though, and the traditional instrument dials are really not as easy to read as they could be. And the perseverance with the J-gate gear selection system looks positively archaic in the face of sequential shifters, while the absence of seat heating was a bit of a surprise given the car's supposed origins.

But you invariably come away from a Jaguar experience with a warm and fuzzy feeling. Even the diesel S-Type exudes this Britishness that gives the car a distinct character separating it from the dominant German marques.

The S-Type has always been a sentimental favourite. The diesel only consolidates this position.