The Efficiency of a Hybrid
Now that diesels are as clean as gas, why would you want one? Diesel engines typically get at least 20 percent better efficiency than a comparable gas engine, which is what a good hybrid delivers. That's clearly the case here, as the EPA rates the TDI sedan at 30/41 mpg city/highway with the six-speed manual. The 2.5-liter five-cylinder gas engine with a five-speed manual gets 21/30; the more powerful turbo 2.0-liter four-cylinder rates 21/31 but requires premium gas. So the TDI is 41 percent more efficient than the base engine in mixed driving.
That's based on the EPA figures, mind you. Real people are reporting better numbers, so VW commissioned an independent test that came up with 38/44 mpg. My results weren't that good, but they were better than the EPA's. My sedan had the six-speed automatic Direct Shift Gearbox, EPA rated at 29/40 mpg. The best I did was 41 mpg on a highway trip of about 30 miles, which included some construction at the tail end. My city results centered around 34 mpg and never dipped below 30 mpg, and the overall mileage for the week was also 34 mpg. The Jetta TDI's mileage is likely to improve over its first 10,000 miles or so, as is true of gas engines.
So, what does this efficiency cost you? Not too much. At $21,990, the base TDI is roughly $2,000 more than the gas-powered Jetta SE, which it's close to in terms of features (see a side-by-side comparison). But you can also subtract from that price the new $1,300 federal tax credit for the diesel and whatever you save in fuel costs. Where diesel fuel used to be less expensive than gas, it typically runs 20 percent more expensive now. Bummer, but if you're getting 40-plus percent better mileage, you still come out on top, and your car is releasing less carbon dioxide. Unfortunately, you can only use up to a 5 percent biodiesel blend (B5) or you'll void the warranty. This is a common restriction among new diesels.
Driving a Clean Diesel
As for the driving, the TDI gives up nothing to the gas versions, in my opinion. Though the engine has lower horsepower, it has characteristically higher torque at low engine speeds. In practice, it seemed my Jetta limited its torque in standing starts, an intentional design to prevent wheelspin. When already in motion, the rush of power when I tromped on the accelerator was more immediate. Overall lag was minimal, which is good to see. So far the Mercedes clean-diesels we've driven exhibit considerable lag when you call for rapid acceleration. Whether it's turbo lag, torque management or transmission hunting isn't clear, but the delay in response is there and it's frustrating.
Overall, the DSG transmission works nicely with this engine, though there are some quirks. It's a little slow to engage and creep forward when you take your foot off the brake, and you'd best engage the handbrake before putting it in Park, because the car rolls a bit more afterward than the average automatic does. (Here in the flatlands, the parking brake isn't always necessary.)
Just Like Gas...Mostly
All told, the TDI differs only in the most obvious ways from the gas versions. It requires fuel that's harder to find, especially in some regions, but most of the drawbacks associated with diesels are gone: It starts immediately and can operate down to -10 degrees F; it sounds distinctive but not particularly noisy; it appears to be smokeless; and the exhaust simply doesn't smell, mainly thanks to modern fuel's decreased sulfur content. It has adequate power, and it even has the same service interval as gas Jettas: 10,000 miles.
Unlike larger clean-diesels, this 2.0-liter four-cylinder doesn't require AdBlue, a urea solution carried onboard, to control the pollution levels. The new emissions controls are virtually trouble-free. One exception is the particulate filter, which traps soot in the exhaust stream and burns it off so it's harmless. The owner's manual notes that the filter can become blocked as a result of the car not being driven long enough distances for heat to build up. "We recommend that you try to avoid making only short journeys," the manual warns. If it does happen, an indicator illuminates on the instrument panel, and the cure is to drive at a speed of at least 37 mph for 15 minutes, according to the manual. An engine speed of 2,000 rpm and 4th or 5th gear is most effective.
Apart from that, the only TDI-specific item I saw in the maintenance schedule was the particulate filter replacement at 120,000 miles. For perspective, many gas engines are dead by this point, where diesels are known for lasting hundreds of thousands of miles. Diesel aficionados are sure to object to this added expense.
The 30 Percent Solution
When TDIs were discontinued in 2007, they made up 30 percent of the roughly 100,000 Jettas sold in the U.S. annually. VW hopes to increase that percentage, though only 2,500 have been imported per month since Aug. 1. Volkswagen of America has requested more for next year, but the current economy might make the point moot. It hasn't stopped buyers yet, though. The 2008 allotment is sold out, and VW says Jetta TDIs ordered now will be delivered in three to four months.
When I refueled the TDI for its return, I was reminded of a long-standing drawback: Diesel fuel is an oil that doesn't evaporate like gas does. It tends to collect on the ground around the pump and on the nozzle handle, and it's easy to track into the car or your house. Even now, every second or third time I fill up my hand gets coated with diesel fuel. The car technology and fuel quality have evolved, but the availability and dispensing (or those doing it) haven't.
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