The example I tried was a Sport Premium - there is also a luxury Sovereign for the same price (£49,995), plus a cheaper Executive at £43,995 - which has firmer suspension and fatter, lower-profile tyres, but still it rides with typical Jaguar serenity even though it grips hard, has a beautifully natural balance and steering with excellent accuracy and firm weighting. This shifts gears with no vague, power-sapping slurring, and it's always smooth.This diesel engine, now calibrated to Euro 4 emission standards and fitted with a maintenance-free particle filter so you never see any smoke, is quite a light unit This makes the XJ feel wonderfully agile. Yet it can average 35mpg, against 27mpg for that petrol version. It's also a more pleasing engine to drive behind, because it pulls very strongly across its speed range and is matched to an excellent ZF six-speed automatic. It's also a rapid Jaguar, able to accelerate just as quickly as the 3.0-litre petrol XJ6, and almost able to match it for top speed. But the Jaguar mountings go a stage further, by using a solenoid-controlled diaphragm inside the mount to expand or contract the fluid space inside the mountings, many times a second, in tune with the engine's vibrations.The result is that the vibration is soaked up before it gets to the XJ6's structure, and the occupants feel nothing. When driving, the only clue that this is a diesel engine is a slight metallic ticking at about 3,000rpm.
Highly sound-absorbent foam under the bonnet and airtight seals between bonnet and engine compartment are the killer tricks here.Inside, there's similar tranquillity. What you're actually hearing is the last vestige of diesel combustion noise, but of clatter and "cackle" there are no traces.So this is as quiet a Jaguar as any. It also matters little that the XJ's engine is smaller than those of its rivals, as its outputs are sufficient for competitive pace and its fuel economy, and emissions, are the best in the class.This is all very fine, but the notion of a diesel XJ, a rattly engine in a car known for its refinement, still seems all wrong. But clever things can be done with acoustics and electronics nowadays, and this XJ is the proof. The bulkhead between engine and occupants is double-skinned, and all the glass is laminated with an acoustically absorbent interlayer. The killer feature, though, is the "active" control of the engine mountings, a first in Europe.Engine mountings filled with silicone fluid are not new, and are a good way of tailoring the mounting to absorb particular vibration frequencies.
Stand outside when it's idling and you would barely know a diesel lurks within; there's just a metallic edge to an otherwise typical V6 hum. You might think that the XJ would be upstaged by the diesel S-type, which is smaller and presumably more rapid as a result. But you'd reckon without the XJ's lightweight aluminium construction, which makes this bigger car lighter than the S-type So honour is upheld. It wouldn't be a..." "A diesel? Exactly," replied the engineer. "We know we need one, but we can't afford to develop our own so we're trying a BMW unit."It came to nothing, but collaboration has indeed proved the solution. The X-type diesel is an improved version of Ford's Mondeo unit (and is now available in 2.2-litre as well as entry-level 2.0-litre versions), while the S-type diesel uses a twin-turbo V6, which is built in Ford's Dagenham factory to a design jointly developed by Ford and Peugeot. A single-turbo version powers the Land Rover Discovery to good effect.And it's the twin-turbo unit, with 207bhp and 321lb ft of torque, which propels the new Jaguar XJ6 TDVi.