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Thursday, September 25, 2008

New VW Jetta Diesel Tops Prius in Fuel-Economy Marathon Test

New VW Jetta Diesel Tops Prius in Fuel-Economy Marathon Test It's this year's ultimate MPG comparison test: the just-released 2009 Volskwagen Jetta TDi diesel against the uber-popular 2008 Toyota Prius hybrid. And has it first, with nearly 500 miles of city and highway driving—and some very surprising results.

Published on: September 24, 2008

As oil prices spiked over the summer, consumers had exactly one choice if they wanted to buy themselves a supercar in terms of fuel economy: the Toyota Prius. There were so few options in the marketplace that Ebay saw record numbers of used economy cars and hybrids flood its auction pages. But what about a brand-new clean diesel ride? We drove the Volkswagen Jetta TDi in Europe right after VW introduced it here last fall—at which point many expected this would-be Prius-beater to arrive stateside in June. It didn't.

Well after a long season at the pump, VW unleashed the 2009 Jetta TDi on the United States last week. So we picked up our new diesel ride and decided to take it right into battle against its natural hybrid foe (before Toyota's 2009 model gives way to the 2010 plug-in hybrid Prius), to the tune of a two-day, 474-mile efficiency showdown.

Our $24,190 Jetta TDi Loyal Edition DSG came fairly well equipped but did lack a navigation system, while at $28,254 our 2008 Prius came with a luxurious $5925 Touring package that included navigation and leather. Nonetheless, we devised a two-day, two-tank regimen to give the fuel economy on both vehicles as thorough a run as humanly possible. Day One crammed in an approximation of a full week's worth of pure city commuting. The second day estimated a typical highway road trip locked on cruise control at a constant speed. Since fuel economy is so dependent on driving style, we accelerated as smoothly and consistently as possible in both tests. Our general rule was to accelerate from each stop with just enough throttle to be as quick as the slowest car leaving the light. This, we believe, best approximates the driving style that an average consumer would adopt with fuel economy as a main priority. So who took the mileage prize? The newfangled diesel or the reigning champ? Here's the bottom line from PM's exclusive test. Warning: The numbers aren't what you might expect.

The City

Our route was a brutal test of both the vehicles' capabilities—and our drivers' patience. It took us 11 hours to travel 238 city miles covering four counties in southern California, under conditions varying from rush hour in downtown L.A. to wide-open, 40-mph country lanes. At no point on this route did we enter a freeway—or even hit a road with a speed limit higher than 45 mph.

The Prius gets its power from a 75-hp 1.5-liter four cylinder with 82 lb.-ft. of torque hooked to a continuously variable planetary gearset. It's boosted by two electric motors for a grand total of 110 hp. As you pull away from a stop under light throttle, the electric motors do most of the work—until about 10 to 15 mph, that is, when the gasoline engine kicks in. The experience, as many a Prius driver has learned, is incredibly smooth and silent.

And as plenty of new buyers will soon discover, under half-throttle or less the Jetta TDi moves with ease that speaks to its impressive torque figure—236 lb.-ft. of torque generated from a 140-hp, 2.0-liter four-cylinder turbo diesel paired to VW's six-speed DSG transmission. The new clean Jetta can loaf along, shifting at around 1500 rpm while still providing enough acceleration to keep up with the flow of traffic. The Prius, on the other hand, needs more throttle to accomplish the same speeds. And the few times we did flat-out acceleration runs to 50 mph or so, it was clear that the Jetta is much quicker. The TDI will even chirp the tires, under the right circumstances.

So where was the more pleasurable place to spend those 11 hours around La La Land? Inside the Jetta—its more traditional cockpit and far more luxurious materials make the new car as cozy as the Prius is cold. The driving position of the Prius makes you feel like you're sitting on the car instead of in it. And since the steering wheel is only adjustable for tilt and not telescope, larger drivers must move the seat a bit too far forward. Yet the Prius, with its funky shifter and digital dash, still conveys that future-car vibe better than anything on the market. As you hustle and joust with traffic, the Prius's quick steering makes it the more nimble of the two. And at just under 3000 pounds, the Prius carries about 200 pounds less weight. But in terms of ride quality and refinement, the edge swings back to the Jetta.

Results (238 City Miles)

Prius: 44.7 mpg /// Jetta: 32 mpg
We expected the Prius to dominate our city test, and it did. After all, the hybrid powertrain meant that every time we hit a red light or traffic snarl, the Prius would sit silently—burning absolutely no fuel. But the Prius's overall 44.7-mpg count is still about 3 mpg less than the EPA city figure of 48. And, interestingly, the Jetta TDi's 32 mpg are exactly four mpg more than its EPA city rating. Still, it's clear that in city-only driving the Prius has no equal—except perhaps a motorcycle. On the open road? Well that's a very different story.

The Highway

Our highway test loop took us from the cool ocean breezes of Santa Monica to the hot desert winds near Palm Springs. We set the cruise control to 65 mph as often as possible to maximize fuel economy.

As was the case in the previous day's city test, it soon became clear that the Jetta was the hot rod of this duo. When we absolutely needed to punch the throttle to merge with traffic, the Jetta left the Prius behind. Shift the DSG into Sport mode, and it will downshift rather brilliantly as you enter a sweeping bend. The Jetta's drivetrain almost encourages you to burn fuel—that is, it's actually fun to drive. And the same cannot be said for the Prius.

On long, undulating freeway bumps, the Jetta is better damped, and it delivered less road noise than the Prius to boot (though the differences between the two are more negligible on the freeway).

Results (238 Highway Miles)

Jetta: 45.4 MPG /// Prius: 44.8 MPG
Since the Prius so handily whipped the Jetta in the city, we were hoping the highway portion might provide a closer test result. And over the exact same route at the exact same speeds and under the same conditions, it appears America has a surprising new fuel-economy champ.

The Bottom Line

It appears clear, no matter what the driving conditions, that the Toyota Prius will return around 44 mpg—if driven with a sane right foot. That's impressive, and that means the Prius remains the most fuel-efficient car on the market. The Jetta falls short in pure city driving, but it does meet (and barely beats) the Prius when it comes to highway fuel economy in our testing.

The price of fuel, of course, remains a big factor. On our test days, regular unleaded was $3.79 a gallon and diesel was $4.09. So on the city drive, which approximated a week's worth of stop-and-go commuting, the Jetta required about $10 more fuel to do the same job. Over a year, that would equate to about $500 if fuel prices stabilize. Granted, that's a big "if," and 500 bucks ain't nothing with an economy like ours. But the Jetta is eligible for a $1300 "Advanced Lean Burn Technology Motor Vehicle federal income tax credit," and $1300 buys a lot of diesel. Looked at another way, $1300 reduces the Jetta TDi's $22,640 base price to $21,340 if you include the destination charge. The base price of the 2008 Toyota Prius, by comparison, is $22,660. So on those terms, the Prius becomes $1320 more expensive than the new Jetta. Surprisingly enough, the Prius is not eligible for this tax credit, although Toyota may be gearing up for that fight.

But tax credits aside, when it comes down to which of these two popular efficient cars is more fun and more comfortable to drive everyday, it's an easy pick: We like the Jetta TDi, and the fuel-economy numbers in the real world for VW's new player make it—gasp!—a legit Prius fighter.