Is Jaguar at a stroke about to answer our biggest criticisms of the XF executive saloon? Now the dust has settled after the epoch-bending new four-door replaced the stuffy S-type in 2008, we've grown used to seeing the wedgy new Jag on our roads and had time to assimilate the XF's place in execville.
CAR Magazine didn't swallow the PR spin and placed the XF behind its BMW 5-series nemesis when we group-tested the XF against its rivals, including the Mercedes CLS and Lexus GS. Our biggest criticism? The XF's weedy 2.7-litre V6 diesel engine, which was nonchalantly dispatched by the BMW 5-series' cleaner, brawnier, more efficient diesel engines. It's a failing confirmed by life with our long-term test XF 2.7 D.
Cue the new family of expanded 3.0-litre twin-turbo diesels arriving in the XF in March 2009 (alongside the new naturally aspirated 5.0 V8 and supercharged XFR). These are important new engines – bound for action in the new 2010 Jaguar XJ, XK sports car, XF, Land Rover Discovery and numerous Range Rovers. It's an unusually swift engine overhaul for the XF, a car that's only been on sale for 12 months...
The new Jaguar XF Diesel S: should the BMW 535d be worried?
Well spotted. The higher-powered XF Diesel S is firmly targeted at the BMW 535d. The old 204bhp 2.7 TD has swollen to 3.0 litres in capacity and now comes in two power outputs: 237bhp and 271bhp.
Jag's not let any journos loose in the lower-powered XF diesel yet, so we're only able to report on the range-topping Diesel S. It's a sign of the times that Jaguar launched its first derv model back in 2003 and here we are – just six years later – with a full, Boxster-baiting performance oil-burner.
Hang on a minute. You mentioned the Boxster?
Artistic licence? Hardly. The Jaguar XF Diesel S is claimed to hit 60mph in 5.9 seconds, within a tenth of Stuttgart's new roadster. And the new V6 has a whopping 600Nm, that's 443lb ft, of torque from just 2000rpm. Jag says 369lb ft of that twist is on tap within 500 milliseconds of idle. Impressive stuff, on paper at least...
The new V6 employs parallel sequential twin turbocharging: most of the time, a variable geometry turbocharger does all the work, leaving the secondary turbo dormant. But when the revs hit 2800rpm, this smaller, fixed-geometry blower kicks in to provide additional puff.
It's different from other twin-turbo systems that use a smaller turbo for low revs and a larger secondary blower for the big work – and Jag claims its system, which isolates the smaller turbo from exhaust gases until needed, reduces pumping losses, consumption and CO2. Also helping the headline figures is a new, third-gen common-rail system using piezo injectors operating at 2000 bar for more precise fuel measurement.
Hard figures please!
Don't you just love modern engines? We're suddenly seeing power outputs spiral and CO2 figures plummet. The XF Diesel S is no different – boasting a third more power, cutting emissions by 12 percent and supping 10% less fuel than the older, weaker 2.7. Result.
Key figures are 179g/km of CO2 and 42.0mpg on the European combined cycle. Which is a winning combo, until you check out the BMW 535d's marginally more saintly figures of 178g/km and 42.2mpg. You can just imagine the oneupmanship at work here.
Ok, so the Jaguar XF Diesel S sounds good on paper. And in the real world?
I'm the custodian of CAR's long-term XF 2.7 D and feel well equipped to judge the accelerative powers of the new Diesel S. And it quickly transpires that they've fixed our biggest gripe over the XF's slovenly performance. This hardly comes as a surprise, Sherlock: wringing 271bhp and, especially, 443lb ft from a twin-turbo V6 means the XF is never wanting for acceleration.
Any gear, any speed, any incline – the Diesel S just leaps forward in that lazy, turbodiesel exec fashion. It might not sound quick, but it sure delivers. The new V6 engines are in fact as hushed and refined as the old 2.7; they're totally in keeping with this model's luxury ambitions.
And is it a BMW 535d beater?
That old chestnut... In a word, no. We're left slightly baffled by Jaguar's acceleration claims, as BMW says its 535d SE hits 62mph in 6.4 seconds. Quite how an 85kg heavier Jaguar with a 15bhp deficit is supposed to be half a second quicker to the sixty benchmark is anyone's guess, even with a 16lb ft torque advantage. Delve deeper into the figures, though, and the XF Diesel S hits 62mph in an identical 6.4sec so there must be a l-o-n-g gearchange stretching the higher, continental sprint time.
Back in the real world, the Diesel S simply doesn't feel to have the catapult thrust of the BM. Where the 535d simply flings itself to the horizon with occasionally worrying vigour, the Jag is merely rapid in most circumstances.
Are we nit-picking? Yes. Don't get wrapped up in the comparison, because on the road the new 2010 XF Diesel S is a brilliant device. It performs strongly when you want to charge, soothes when you want to cruise and promises improved economy (although we have yet to test this independently).
And the rest of the XF package?
This is no mid-life facelift, merely an engine change. So the rest of our XF verdict remains remarkably unchanged. This is a low-slung, four-door only exec for those who want a change from the Teutonic opposition. They won't be disappointed. The XF goes, steers, stops and entertains like the exec best and we still love that interior package with its vodka bar cool lighting and pared-back minimalist cabin design.
It's a shame the Jaguar XF Diesel S is going to be compared with the BMW 535d so much. The BM is an extraordinary car, the Jag a merely excellent one. In isolation, it's a cracking diesel exec that happens to cost £3000 less than the 535d. It might not feel bullet fast, but believe us, the thrust on tap in the new S now means nobody can accuse the diesel XF of being too slow.