By Bill Saporito and Turner Cowles
Updated: September 21, 2015 2:36 PM ET | Originally published: October 3, 2014

In our October 2014 review of the 2015 Volkswagen Golf TDI, we reported that VW, thanks to the power of German engineering, seemed to have pulled off a diesel hat trick: great mileage/range, great engine performance, and yet a cleaner burn.

Instead it turned out to be a parlor trick—watch the pollution disappear! VW’s dirty secret: The TDI engines contained software that switched on its lower-emission technology only when inspections were due. The rest of the time, the TDIs were spewing nitrogen oxide at higher-than-legal levels. VW did this, allegedly, because the engines run better without the pollution controls engaged. That’s German engineering, too, apparently.

The Feds busted VW on this legerdemain, but now owners of VW and (some Audi) diesels made since 2008 have a choice: take the car in to be serviced, and thus lose some performance from the overhauled engine; or do nothing, and add to the nation’s pollution load. You could get rid of the car, too. But the trade-in value just crashed, and the vehicle is depreciating rapidly. VW may be pressured into offering something very special on trade-ins—and it ought to—so stay tuned. In the meantime, maybe you can buy a carbon offset to assuage your conscience.

The original review:

Diesel has been a dirty word in the American automobile industry for too long. We can’t seem to get the idea out of our heads that “diesel” means smelly, sluggish, expensive and, well, European.

And that’s always been perplexing to European car manufacturers, who have been continually improving the technology, making it cleaner and more efficient.

We may be entering a diesel renaissance in the U.S., however. Sales of diesel-powered cars increased 25% percent during the first six months of 2014, according to HybridCars.com. That’s in some measure because American car makers are increasing the number of diesel options. Chevrolet has added a 2.0L diesel option to its popular Cruz lineup, and more diesels are popping up in pickup trucks such as Chrysler’s Ram. Next year Chevy will add a diesel to its midsized Colorado and GMC Canyon midsized pickups. Mazda is also joining the party.

What’s driving diesel ahead? For one, diesel engines are much cleaner than in the past. Chevy’s Clean Turbo Diesel generates 90% lower nitrogen oxide emissions than earlier models, says the company. That makes environmental regulators happy.

But a 46 m.p.g. highway efficiency rating in the Cruz is what makes buyers happy — and it’s one reason the Cruz power plant was the third diesel engine to make WardsAuto’s top 10 engines list this year. The other two include the 3.0L V-6 turbo diesel that powers both the Ram 1500 pickup and the new Jeep Grand Cherokee; the 3.0L, 6-cylinder turbo diesel pushing both the BMW 535d sedan and X5 crossover rounded out the list.

Even better, the premium you have to pay for the diesel over a gasoline engine — the step-up price — is narrowing. In Volkswagen’s new 4-door Golf, for instance, the 2.0L TDI diesel version is priced at $21,995 for the basic S trim package compared with $20,695 for the 1.8L gas-powered model. “When you look at the step price vs. fuel efficiency, customers are seeing value,” says Doug Skorupski, powertrain strategy manager. The Golf diesel is rated 30 m.p.g. city/45 m.p.g. highway, making it 9 m.p.g. better on the interstate than then gasoline model. And some reviewers are reporting much higher figures for the diesel’s efficiency. On a practical basis, that means you can go weeks without filling the tank.

Does it pay to drive a diesel? Depends on how much you drive, how long you plan to keep your car and how much you beat it up. Diesels are more fuel efficient because you get more compression out of the engine and thus more power compared with gas. Diesel fuel is currently priced about 36c a gallon more than gasoline ($3.457 vs. $3.814, according to the U.S. Energy Information Agency), although that gap is narrower in some places, such as California.

At those prices, you’d have to drive about 100,000 highway miles to erase the premium you paid for the diesel engine. But diesels tend to be lower maintenance, and their resale value is higher, making total cost of ownership lower. “These diesel engines really like to work,” says Skorupski. “No matter how you tend to drive the vehicle, they maintain efficiency.” Translation: You can beat the hell out of them. VW says that 23% of its sales are diesels, but 45% of Golf buyers are choosing diesel.

VW has been selling diesels in the U.S. forever and recently launched its redesigned 2015 Golf, three versions of which come with the company’s TDI (for “turbo direct injection”) diesel engine. The new Golf, the 7th version of this venerable model, represents badly needed fresh merchandise for the VW portfolio, which has suffered in the U.S. for the lack of new product.

And the diesel version can easily make a case for itself. For one, the TDI answers one of the old issues about diesels, that their power isn’t matched by their acceleration. Engineers refer to it as torque curve; as diesels go up rpms, they lose their giddyup.

That’s not the case in the TDI. There’s more than enough torque available, even if the trip up the gears is noticeable on the DSG automatic transmission. VW has made this Golf about two inches longer, an inch lower, and half an inch wider. On the road, the TDI is one of the quietest cars I’ve driven all year. Inside, you may not be dazzled by the styling, but VW sedans have always been about function and value over silliness.

So have diesel owners in general. Remember those Volvo diesel owners you made fun of in the 1980s because of their cars’ sluggish performance? Those days are over. Road & Track reports that Volvo’s five-cylinder, diesel/electric V60 hybrid delivers more torque than a Lamborghini Gallardo. Sensibly, of course.

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