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July 24, 2013

News & Features

Auto review: Porsche Cayenne Diesel racks up the mpgs

New York Times News Service

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The Porsche Cayenne Diesel gets 29 mpg in highway driving. (Porsche)

You won't get altitude sickness in Sacramento, Calif., where 20 feet of elevation is considered high ground. Drive 100 miles east, though, and you'll be in Truckee, a Wild West-flavored ski town perched in the Sierra Nevada at about 6,000 feet. Sacramento-to-Truckee is the kind of drive that can strain cooling systems and test the nerves of truckers once Interstate 80 starts heading back downhill. Over this route, with its mile-plus of sheer vertical ascent, the 2013 Porsche Cayenne Diesel averaged 26 miles per gallon. If you're wondering why Porsche now makes a diesel, that number probably answers your question.

Diesels, with their ample low-rpm torque and thrifty mileage, make all kinds of sense for SUVs. The question for Porsche was whether a diesel could be coaxed to perform in a sufficiently Porsche-like way, because the Cayenne is an SUV that tries to comport itself like a jacked-up sports car. Thus, bolting a clattering iron anchor under the hood would be unacceptable no matter the EPA numbers it cranked out.

2013 Porsche Cayenne Diesel
  • What is it? The only new diesel Porsche Americans can buy
  • How much? $56,725 base; $91,990 as tested. Notable options include "natural" leather interior in espresso ($5,165), air suspension ($3,980), panorama roof ($1,850) and off-road underbody protection ($1,330). The latter is not to be confused with stainless steel front and rear skid plates, which cost $1,480
  • What's under the hood? 3-liter diesel V-6 (240 horsepower, 406 pound-feet of torque) with an eight-speed automatic transmission
  • Is it thirsty? By SUV standards, it's practically a Prius: 20 mpg city, 29 mpg highway

But diesels don't naturally lend themselves to Porsche-type thrills. The difference between a diesel motor and an equivalent gas counterpart is the difference between a glacier and an avalanche. The glacier advances, inexorable, crushing everything in its path with sheer relentless power. The avalanche erupts with a spate of energy, quick and violent, but afterward there might well be a few trees left standing. The trick for a company like Porsche is injecting the diesel's mighty ice-sheet unstoppability with a little bit of avalanche urgency.

And, yes, these are the kind of metaphors that spring to mind when you're driving through Donner Pass.

The Cayenne's 240-horsepower 3-liter diesel V-6 (shared with several other vehicles in the Volkswagen/Audi empire) enlivens its responses with a variable-geometry turbocharger that continually adjusts the angle of its vanes to keep the power flowing. It's down on power compared with the 265-horsepower diesel offered in the BMW X5, but that vehicle has a six-speed automatic; the Porsche enjoys the increasingly ubiquitous ZF eight-speed.

Two extra gears make a big difference, enabling highway mileage of nearly 30 mpg while delivering off-the-line acceleration that nearly hangs with the more powerful BMW. The V-6 has a fairly narrow useful range of engine speed: by 3,000 rpm, you're nearing the horsepower peak and are well past the torque plateau of 406 pound-feet. So the ZF's frenetic upshifts keep the motor spending more time where it's happiest, from 1,750 to 2,500 rpm. In the mountains, where most gas-powered SUVs are downshifting and laboring up the grades, the Cayenne Diesel just spins up its turbocharger and calmly steams along.

Porsche says the Cayenne Diesel accelerates to 60 mph in 7.2 seconds, slightly quicker than a gasoline V-6 model with an automatic. (Yes, you can get a stick shift with the gasoline V-6.) But it's also a long way behind the more outrageous gas-powered Cayennes. The Diesel tricks you into thinking it's quicker than it really is, though, because the power arrives in short, cleanly defined bursts rather than the comparatively long trip to the redline with gasoline engines.

And once you're moving, you can easily forget what's under the hood, because the Diesel drives like any other Cayenne, with its priorities clearly oriented toward performance. Even with the optional air suspension, the ride is firm, the steering weighty and serious. The Diesel's rear end incorporates brake-based torque vectoring to increase agility, the same method employed on the 911 Turbo.

The Cayenne Diesel starts at $57,575, which is $7,000 more than the gasoline-powered V-6 but $14,300 less than the Cayenne Hybrid. While Mercedes-Benz positions its diesel-powered GL350 as a base model, Porsche's pricing implies that, despite giving up 60 horsepower, the Cayenne Diesel is an upgrade over the gas V-6.

Well, they're right. It is.

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