Although the majority of diesel engines are sold in heavy-duty trucks, many people regard diesels as the great hope of the passenger car class in the midst of rising fuel costs and elevating concern over carbon-dioxide emissions. Compared to gasoline-electric hybrids, diesels are less complex in design yet they're usually just as fuel-efficient. In addition, most people find the driving experience more, well, normal.
Unfortunately, diesels have had difficulty complying with the federal Tier 2 emission regulation, which placed tighter limits on nitrogen-oxide (NOx) emissions. (Nitrogen oxides cling to particles in the air, forming smog.) This has forced auto manufacturers to explore a range of new emissions treatment technology for U.S.-bound vehicles and, naturally, this adds cost and complexity. The upshot is that American consumers wanting a diesel engine in a light-duty 2008-model-year vehicle have just a handful of choices. Plus, these cars are on sale in only 42 states, as eight states, including California and New York, have adopted even stricter emission standards.
If you want more options, we'd advise waiting until 2009 when the ever popular Volkswagen Jetta TDI is slated to return to the U.S. as a 50-state vehicle. Beyond that, the future looks good for diesels in the U.S., in large part because Honda, a long-time proponent of hybrids, is now investing heavily in diesel technology for use in its midsize cars and SUVs.
Jeep, Mercedes-Benz and Volkswagen are the only manufacturers offering diesels in light-duty vehicles for 2008. The Mercedes-Benz E320 Bluetec is the only sedan in the group, and it's worth serious consideration if you're interested in an elegant midsize luxury car that just happens to have impressive 23 mpg city/32 mpg highway fuel economy estimates, even under the EPA's more stringent rating system. Not only can the E320 be equipped with all manner of luxury accoutrement, with 400 pound-feet of torque, this rear-drive diesel sedan is quick off the line -- 60 mph comes up in just 6.8 seconds. Although the E320 Bluetec is officially offered for sale in only 42 states, Mercedes recently initiated a special program in California, where consumers will be able to lease this sedan for two years or 24,000 miles. Expect this program to spread to the northeastern states during the 2008 calendar year.
If you don't want a sedan, there are four diesel SUVs to choose from -- the Jeep Grand Cherokee CRD, Mercedes-Benz GL320 CDI, Mercedes-Benz ML320 CDI and Volkswagen Touareg 2 V10 TDI -- plus one very large wagon, the Mercedes-Benz R320 CDI. In this group, the Grand Cherokee and the GL320 merit close attention. For 2008, Jeep will be offering a 3.0-liter turbodiesel V6 as an option on all Grand Cherokees and it's worthwhile in more ways than one: Fuel economy is usually dismal on Grand Cherokees, but with the diesel, it earns a 17 city/22 highway rating -- as good as many crossover SUVs. Then, there's the torque factor: A diesel Grand Cherokee can tow up to 7,400 pounds, which is identical to its tow rating with the much thirstier 5.7-liter "Hemi" V8.
Larger families should give serious thought to the seven-passenger Mercedes-Benz GL320 CDI. The diesel version of Mercedes' largest SUVs offers all the virtues of the V8 models, including a spacious and upscale interior, agreeable driving dynamics and a fair amount of all-terrain capability. With a turbodiesel V6 providing the motivation (just as in the E320), acceleration is respectable rather than explosive, but most owners will be more than happy to give up a little speed in trade for better mileage: The biggest Benz carries an 18 city/24 highway EPA rating.
You can expect a similar performance/fuel economy compromise from the five-passenger ML320 CDI and six-passenger R320 CDI, which have the same drivetrain and identical EPA ratings. However, given that only four adults can ride comfortably in the ML320, most families will find the E320 Bluetec sedan a better value. And for larger families, the GL320 SUV is a bit more practical and useful than the R-Class wagon.
Volkswagen's Touareg V10 TDI is the oddball of the small diesel population, as it's not intended to be the frugal, fuel-efficient option for would-be Touareg 2 buyers. Rather, it's the high-line model, and with a 5.0-liter V10 that generates 310 hp and an enormous 553 lb-ft of torque, it's one of the quickest SUVs money can buy. The tradeoff is that its fuel economy numbers are mediocre -- the EPA rates it just 15 city/20 highway.