This XF test mule is powered by what Jaguar says is it most efficient engine yet.
It's a new 2179cc four-cylinder four-cylinder, 16-valve common rail turbodiesel - installed longitudinally for the first time - for which Jaguar quotes 140kW and 450Nm.
The test car, it says, returns 5.4 litres/100km and emits only 149g/km of CO2.
The new engine has a water-cooled turbocharger with low-friction pistons, new injectors and a new crankshaft and, because it's mounted in line with the chassis, Jaguar's engine boffins have been able to fit a new sump casting that allows the stop-start system to operate more efficiently.
It uses a new crankshaft sensor and fuel rail pressure holding system to restart the engine more quickly. With conventional systems the engine needs to shut down completely before restarting, which can cause an irritating delay when the car stops for only a moment - such has when entering a traffic circle.
Jaguar says the new system can restart the engine while it's still turning over at 400rpm, for a seamless pause-and-go at circles and yield signs - and still increases overall fuel efficiency between five and seven per cent.
The new engine is also the first to be mated to ZF's new, eight-speed automatic transmission. The top two gears effectively act as overdrive gears, giving the new engine long legs as well as swift acceleration when needed.
The test mule, says the maker, will sprint from 0-10km/h in 8.5sec and top out at 225km/h.
The development engineers have also concentrated on sound deadening around the engine and bulkhead, as well as active engine mounts to reduce vibration, making this XF one of the most refined diesels in its class.
And it's close to production; the new engine and gearbox will available in a revised XF model to be announced at the New York motor show.