Around the Block: Diesel Efficiency With a Solar Enhancement

TESTED: 2013 Volkswagen Beetle TDI convertible

WHAT IS IT? The only diesel-powered convertible available in the United States.

HOW MUCH? $28,690 base, which is $2,900 more than the base gasoline-powered convertible; $29,990 as tested with the Sound and Navigation package.

WHAT’S UNDER THE HOOD? A 2-liter in-line diesel 4-cylinder with turbocharging and direct injection; 6-speed manual or dual-clutch 6-speed automated transmission.

IS IT THIRSTY? Not at all: at an E.P.A.-rated 28 m.p.g. in town and 41 on the highway, it’s the stingiest droptop in the nation.

In 2006, I drove a Saab 9-3 diesel convertible in Italy. Aside from an unfortunate incident when a bird guano-bombed my head near Lake Como, the top-down experience was remarkably pleasant.

Diesels are no longer stinky, and I find their signature mechanical growl quite appealing — the muted compression-ignition clatter and whistle of a turbocharger remind you that you’re piloting a machine and not just playing a realistic car-themed video game.

Further, that punchy Saab could eke out around 40 miles per gallon at sub-autostrata speeds. Saab didn’t sell that car in the United States, but I returned home wondering why not.

Diesel convertibles make all sorts of sense, given the relaxed, torque-heavy power delivery of diesels and the mellow mien of top-down driving. But if you want such a vehicle, your decision tree is simple indeed: in America, all paths lead to the Volkswagen Beetle TDI convertible. I suppose you could try to build your own diesel convertible, but that would be quite a project. Ask me how I know.

Volkswagen offers the droptop diesel Beetle with a 6-speed manual transmission or a 6-speed DSG automated manual.

Because only a subset of Beetles are convertibles, and a minority of Beetles convertibles are diesels, and the bulk of those will be automatics, a manual diesel convertible like the one I tested will be rare. I’m thinking they’ll build about five of these.

And those five cars, I’ll wager, will be bought by people who may not otherwise consider a Beetle.

This is a car that trades heavily on its styling, because design is the main differentiator between a Beetle and a Golf, Jetta or Eos. But because you can’t get a convertible Golf or a diesel Eos, the Beetle is the sole conduit to the droptop diesel experience.

I happen to like the shape of the recently redesigned Beetle, which went in a distinctly Porsche-like direction, but this is still a polemic machine. The Beetle convertible is a car for extroverts, a fact reflected by its jaunty color palette, rife with names like Yellow Rush and Denim Blue. For added attention in traffic, the power top can operate at speeds of up to 31 m.p.h.

Volkswagen says it used a cloth convertible top because it “allows for a roofline that’s more like the original 1949 type 15’s.” All right, if you say so. VW also allows that the decision may have had something to do with the fact that a folding hardtop would have required about an extra foot of rear overhang or a small trailer in which to stow it.

As it is, the soft top’s seven-layer sandwich of rubber, fabric and insulation does a tidy job of keeping rain and noise outside. Retracted, it piles itself into a neat little stack behind the rear seats, preserving the 7.1 cubic feet of trunk space.

Thicker windshield pillars, under-floor bracing and an automatic pop-up rollover-protection system contribute to the convertible’s 223-pound weight penalty over an equivalent TDI coupe. But at 3,296 pounds, the softtop Beetle is still amply motivated by the 2-liter diesel’s 140 horsepower and 236 pound-feet of torque.

The TDI convertible exudes a feeling of easy power, marshaling that impressive reserve of torque to muscle off the line and lazily cruise uphill without demanding a downshift.

The little diesel runs out of breath relatively quickly, but hey, man, what’s the rush? The top’s down. Enjoy yourself.

Watch the boost gauge on the dash binnacle swing over as the turbocharger spools up. Use the adjacent lap timer to ensure that you reapply sunscreen at appropriate intervals. The Beetle’s lap timer is like the Porsche Sport Chrono’s laid-back acoustic-guitar-playing cousin who’s on the seventh year of his undergrad degree.

While you’re driving about listening to chill tunes and looking for tasty waves, the TDI will be squeezing a federally rated 28 miles per gallon in town, and 41 on the highway, from each gallon of diesel fuel.

Volkswagen says those numbers make this the most efficient convertible on the road today, but the key word is “today,” because the 1992 Geo Metro LSi Convertible managed 41 m.p.g. on the highway and 35 in the city.

I don’t think VW needs an asterisk on its claim, however, because the Geo had 3 cylinders under the hood, and if you started a 0-to-60 m.p.h. run in 1992 you might not have finished it yet.

So if you want the wind in your hair and 41 miles per gallon, you really have only one choice that does not involve a motorcycle license, a preowned Geo or moving to Europe.

Stay away from the unleaded pumps and watch out for birds.