This may be automotive journalist blasphemy, but diesels aren't always a good thing. And I don't mean that from an emissions standpoint. Sometimes the diesel in question isn't a good engine, and/or is a bad fit for the cars to which they're fitted. Our long-term Jaguar XE diesel is a textbook case of both issues.

The first issue becomes apparent from the moment the 2.0-liter turbodiesel four-cylinder fires up with all the clattering, tapping and ticking that can only come from a compression-ignition engine. It's far from the shaking and knocking of full-size diesel trucks of a few decades ago, but it definitely feels a generation or two behind other diesel cars. For instance, we had a diesel Chevy Cruze in the office, which was quieter and smoother than the Jaguar despite a base price roughly $10,000 less. It becomes a bit smoother and less raucous as revs increase, but the volume remains rather high, making it sound as though the engine is struggling more than it is. Though, to Jaguar's credit, the company has managed to keep virtually all engine vibrations from entering the cabin.

Now, the diesel engine's voice would be less problematic if it provided some engaging performance, but, outside of the high fuel-economy numbers, there's hardly any to be found. This may seem surprising considering the Jaguar's 318 pound-feet of torque, but that torque figure lasts only briefly from 1,750 rpm to 2,500 rpm. After that, the torque rapidly falls off, and you don't see the Jag's meager 180 horsepower peak until 4,000 rpm -- not far off of the engine's roughly 5,000-rpm redline. As a result, the XE has adequate passing power and around-town shunt, but anytime you want to play with more revs, it faceplants. But at least it does nail, and even exceed, its 40-mpg highway fuel economy rating without trying.

Jaguar XE 20d engine

The faults of this diesel engine are then exacerbated by the fact that it's in such a smooth and fun car as the XE. It positively glides across rough city streets and highways, keeping the chassis steady and its passengers soothed. Coupled with a quiet cabin, the XE is a peaceful place to be. At least it would be if the diesel didn't rudely interrupt every time the throttle pedal is pressed.

Through some sort of black magic, the XE handles about as well as it rides. The incredibly sensitive and accurate steering is superb. It feels like adjustment knobs on a high-end stereo -- weighted perfectly and fine enough to get it right where you want it. It's paired to a confident chassis that's eager to turn in and clearly up for being driven hard. Sadly, the sluggish diesel just doesn't answer the call for heart-pounding power or sound. It's like pairing a fine wine with a block of store-brand cheddar.

For all of this griping, I can end on a positive note. For one, Jaguar XE's charming chassis is not solely saddled with the diesel. There are other engine options for it, including a turbocharged four-cylinder, two supercharged V6s and now a supercharged V8 that are surely more fitting for the athletic sports sedan. And the gasoline four-cylinder is actually cheaper than the diesel and has more horsepower. Also, even though diesels aren't right for every vehicle, and some of them aren't right for any, there are good ones out there. In the right car, it can enhance the experience, as we learned with the aforementioned Cruze diesel. Basically, engines are like tools -- you want to use good ones and you have to use them for the right purposes.

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