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Text by Dubspeed Media Staff, Carl Modesette and Zerin Dube
Photos by Zerin Dube and Matt Chow, additional photos by respective manufacturers

As fuel prices in the United States continue to rise, consumers are beginning to direct their attention further away from traditional gas-guzzling family trucksters and more towards alternatives that are actually halfway economical. The problem is, at least in this writer’s humble opinion, that the media (and industry) buzz is focused solely around hybrids. While certainly a viable and increasingly available option, little if any attention is being paid to other alternatives, namely diesels. Thus, when the opportunity to sample Mercedes’ latest offering presented itself in the form of the 2006 E320 CDI, we jumped at the chance.

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While our 2006 model test car is new, Mercedes is no stranger to the diesel passenger-car market. In fact, Mercedes introduced the world’s first diesel passenger car, the 260D, in 1936. Just 20 years ago, 75% of Mercedes-Benz vehicles sold in the United States were diesels. Introduced in the US in 2004, the CDI has enjoyed much success due to its outstanding fuel efficiency and performance.

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Rather unassuming in appearance, our test car isn’t visually distinguishable from its gasoline-powered brethren save for the discreet CDI badge on the rear decklid. CDI is Mercedes-speak for Common-Rail Direct Injection, a fuel-injection system that electronically maintains a constant level of high fuel pressure (23,300 psi!) in each of the engine’s six injector valves. This type of system softens diesel power pulses, resulting in smoother, quieter, and more powerful performance, according to M-B.

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Upon turning the ignition key, you’re aware that there’s a diesel under the hood by the telltale diesel clatter, but the noise is certainly not obtrusive. After a few minutes of warm-up, this clatter subsides, and engine noise is no more intrusive than traditional gasoline engines. Once underway, it doesn’t take long to discover the mammoth strength of this CDI engine. Rated at 369 lb-ft of torque, available from 1800-2600 rpm, it pulls authoritatively away from a standstill with only moderate throttle application. While certainly entertaining, the real beauty of the CDI’s torque curve is found in the subtleties of everyday driving – merging into freeway traffic, passing, and exiting parking lots onto busy thoroughfares. Instead of mashing the go-pedal to the floor, waiting for several downshifts, and praying for the best as the tachometer swings wildly toward redline, simply roll lightly into the throttle and let the torque take care of business. This is quite a paradigm shift from traditional gasoline engines that build power and torque as RPM’s rise. Marketing that focuses on lofty horsepower figures – which look great on paper - fails to take into account the real-world tractability of torque.

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Torque aside, the true calling of the E320 CDI is improved fuel economy. EPA estimates of 27 mpg city and 37 mpg highway compare quite favorably to the gasoline-powered E350’s 19/27 figures. In mixed city and highway driving I observed anywhere from 25-28 mpg, and on the open highway, I found it difficult to get any worse than 30 mpg. Either way, range is incredible considering the 21.1 gal tank – it’s actually feasible to make it from Houston to El Paso on a single tank of fuel! Using the EPA city estimates for fuel consumption and driving 15,000 miles per year, the CDI will consume 234 gallons LESS fuel than the E350. At current prices, that results in nearly $600 annual fuel savings. Considering that the price differential for the CDI is only $1,000 more than the base E350 (E320 CDI price-as-tested of $55,465) , the economics are a no-brainer.

And what of the hybrids? Let’s compare two popular models: the 2006 Honda Civic Hybrid and the 2006 Ford Escape Hybrid:

The Escape Hybrid offers 155 horsepower and 124 ft-lb of torque, and EPA figures of 36 city / 31 highway for a base MSRP of $27,515. The base Escape offers 153 horsepower and 152 ft-lb of torque, and EPA figures of 22 city / 26 highway for a base MSRP of $19,995. Using EPA city estimates for fuel consumption and driving 15,000 miles per year, the Hybrid will save 265 gallons of fuel, translating into $663 annual fuel savings.

The Civic Hybrid offers 110 horsepower and 123 ft-lb of torque, and EPA figures of 49 city / 51 highway for a base MSRP of $21,850. The base Civic offers 140 horsepower and 128 ft-lb of torque, and EPA figures of 30 city / 40 highway for a base MSRP of $15,360. Using EPA city estimates for fuel consumption and driving 15,000 miles per year, the Hybrid will save 294 gallons of fuel, translating into $735 annual fuel savings.

On the surface, things look great – both hybrids appear to conserve between 250 and 300 gallons of fuel yearly, translating into an average of $700 yearly fuel savings. However, note carefully the price differential – the Hybrid Escape comes at a $7520 price premium, and the Civic Hybrid comes at a $6490 price premium. Even with the $2000 one-time Federal Income Tax deduction for Hybrids, the cost of entry is rather steep. Also keep in mind that horsepower and torque are, at best, only comparable to standard models. All of a sudden, it’s not so easy being green.

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So if diesels are so great, why don’t we see more of them on the road…or in dealer’s lots? The primary obstacle in diesel progress has been emissions – particulates and oxides of nitrogen, in particular (if you’ll forgive the pun). Already prevalent in Europe, low-sulfur diesel fuel (15 ppm) is key in facilitating lower emissions (current diesel fuel in the US is 500 ppm). The good news for stateside diesels is that this fuel should become available in the US near the end of 2006. My prediction is that we’ll start seeing many more diesel powerplant options from more and more manufacturers shortly thereafter. In fact, J.D. Power and Associates predicts that the diesel passenger car market in the US, currently at 3.4%, will quadruple by 2015. In Europe, diesels currently account for more than 50% of the market. Volkswagen and Mercedes already offer diesel powerplants in passenger cars, and the Big Three have been very successful with their diesel-powered trucks. GM, Ford, Honda, and Nissan are all reportedly investigating diesel technology for both cars and trucks.

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The E320 CDI might not be the best thing since sliced bread, and certainly won’t single-handedly change the face of worldwide conservation efforts, but what it stands for is much bigger than that. It represents an outside-the-box thought process that’s focused on refining and perfecting existing technology instead of leaping off the deep end into uncharted technological waters. In the words of Mercedes, diesel technology offers excellent economy, longevity, and robustness without compromising on driving enjoyment. I never liked changing spark plugs anyway.