Although some may point to a Jaguar's sensuous design as its hallmark, in my view the carmaker's engines have always been the key to its soul. Jaguar's famous dohc inline six-cylinder XK engine appeared at a time when some competitors were still trumpeting the switch to pushrods and overhead valves. Jaguar's one-two-three finish at Le Mans in 1988 proved that its V12, by then two decades old, was still a viable concept for a specialized sports car maker. The company's latest supercharged V8 continues to display Jaguar's engine design prowess. So when I learned that in some parts of the world more than 70 percent of new cars that Jaguar sells have diesel engines, I was shocked. I set about finding out what a diesel Jaguar was like to drive.
Diesel-powered passenger cars are sort of a hobby of mine--I have sampled offerings from the major automakers for more than twenty years. Over that time diesels have gone from the smelly, noisy, and painfully slow to clean, quiet, efficient, and surprisingly powerful. Getting to drive a diesel Jaguar was no more difficult than asking. It helped that I happened to be at the world launch of the new XF, XFR, and XKR models, and although driving the diesel XF wasn't on the official schedule for North American journalists, I pleaded my case and a brilliant white turbocharged diesel XF appeared in front of the hotel early one morning.
The 3.0-liter engine in the XF isn't the first diesel from Jaguar. In fact, it replaces a 2.7-liter engine that made its debut in 2004 in the S-Type sedan; Jaguar had introduced diesels with the Ford-derived X-Type in 2003. Somehow, though, the Jaguar diesel had never appeared on my radar. The new AJ-V6D Gen III engine bristles with technology--in many ways it's more technically advanced than the also-new 5.0-liter V-8 AJ-V8 Gen III gasoline engine. The 3.0-liter V6 diesel has a cast-iron cylinder block made from compact graphite iron with a higher tensile strength than the more common grey cast iron. This allows the block to be smaller than it would be if it were made with the conventional material. The aluminum cylinder heads employ four valves per cylinder and a healthy 16:1 compression ratio.
At the engine's heart is a parallel sequential turbocharger system. A variable-geometry primary turbocharger provides all of the boost pressure for most situations, while a second turbocharger is isolated from the exhaust stream and engine inlet tract and so consumes no power. When the engine speed climbs above 2800 rpm, valves open to bring the second turbocharger online within 300 milliseconds. Jaguar claims that the new AJ-V6D Gen III engine can deliver 369 lb-ft of torque within 500 milliseconds from idle. Fuel delivery has also been enhanced with a common-rail direct injection system that operates at 2,000 bar (29,400 psi) and whose individual piezo-electric injectors fire up to five times on each combustion cycle. The piezo crystals in these injectors are located near the injector tips and buried deep within the cylinder head to reduce engine noise. Other noise reduction techniques include optimized camshaft covers, front covers and the engine sump that includes a polymer layer between two layers of steel to help deaden noise transmission.
The diesel market is important enough to Jaguar that it actually offers two versions of its diesel engine. The standard version produces 240 hp at 4000 rpm and 369 lb-ft of torque at 2000 rpm, while an "S" version produces 275 hp at 4000 rpm and an impressive 443 lb-ft of torque at 2000 rpm. The "S" engine produces 33 percent more power than the previous 2.7-liter engine while reducing carbon dioxide emissions by 12 percent. In European fuel economy tests--which bear no relation to our own EPA economy figures--it returned combined city and highway economy as high as 42 mpg, which also improves upon the 2.7-liter by 10 percent. In both cases power is transmitted through the same six-speed automatic transmission that the V8s use.
I press the starter button to bring the diesel V6 to life. There is the faintest hint of "clatter" as the engine starts, and then it settles down to a just-perceptible idle. Leaving the hotel grounds, the XF gives no indication that it's anything but the same quiet and refined V8 sedan I drove two days earlier. The hotel is located at the top of a steep hill, which provides the perfect chance to sample the engine's ample torque. From a dead stop, pointing uphill on a 10 percent grade, the thrust is impressive and response is nearly instantaneous. With a reported zero-to-60 time of 5.9 seconds, the diesel XF is plenty fast and its surplus of torque means that it gives up little to the naturally aspirated gasoline V8, which does zero to 60 mph in 5.5 seconds. The only sense that this is a diesel is an ever so slight rattle on full acceleration, the low engine speeds at which the transmission shifts gears, and all that glorious torque.
Jaguar has no present plans to bring diesels into the U.S. market. The new 3.0-liter engine can meet U.S. exhaust emission regulations in 42 states, but would require additional exhaust after-treatment to meet rules in places like California, the same problem faced by Mercedes-Benz and Volkswagen with their diesel offerings.
Now, if this were a normal car review, I'd leave it at that. However, allow me to editorialize a bit. As wonderful as the supercharged, gasoline-fueled, 461-hp V8 is in the XFR, and as much as I enjoy driving absurdly powerful automobiles on racetracks and winding mountain roads, I have to believe that the remaining days for such cars are numbered. At some point even car enthusiasts have to face the realities of social responsibility. I used to think that was a bad thing. But when I drive a car like the diesel XF I'm filled with hope. It's fast, quiet, comfortable, and provides everything a Jaguar owner would expect, all while reducing fuel consumption and emissions. I cannot help but think that although hybrids and electrics will fill the need for commuters and urban vehicles, for those of us who enjoy performance and driving, our futures may lie with high-tech diesel.