1998 Volkswagen New Beetle

One of the best-kept secrets of Volkswagen's wildly popular New Beetle is the car's turbocharged diesel engine, which delivers lively performance and nearly 50 m.p.g. on highways.

Volkswagen said only 10 percent of New Beetle buyers have opted for the car with the 1.9-liter, 90-horsepower TDI (Turbo Direct Injection) four-cylinder diesel.

That's partly because the New Beetle diesel's $16,475 base price is appreciably higher than the $15,200 cost for the gasoline-engine New Beetle, which has a 2-liter, 115-horsepower four-cylinder.

Also, many Americans have bad feelings toward diesel motors because most diesel-engine cars have been noisy, smoky and slow.

Not so with the New Beetle TDI diesel. Volkswagen set out to shatter the perception of diesel cars with this model. The super-efficient TDI is quiet, smooth, strong and meets stringent exhaust emission standards, emitting far less carbon dioxide than a comparable gasoline engine.

The well-mannered TDI diesel's solid performance characteristics are the result of a big advance in diesel technology, whereby fuel is injected and ignited directly in the engine's cylinder head. Previous diesel motors ignited fuel in a separate combustion prechamber, offset from the cylinder head.

As the TDI name implies, Volkwagen also uses exhaust turbocharging and charge air cooling to further enhance the efficiency of this direct injection compression ignition process.

Gone are the delayed, smoky starts of old diesels. And one must listen hard to hear the ``rattle'' sound that was pronounced in former diesels.

Moreover, the New Beetle diesel delivers an impressive, EPA-estimated 48 m.p.g. on highways and 41 in the city with the standard five-speed manual transmission. The figures are 44 highway, 34 city with the $875 four-speed automatic transmission.

Those numbers easily beat the figures for the gasoline-engine New Beetle: 23 city and 29 highways with manual and 22 city, 27 highway with the automatic.

The 2,811-pound New Beetle diesel is slightly heavier than the 2,747-pound gasoline-engine version. But the diesel engine generates more torque than the gasoline motor--149 foot-pounds vs. 122. And one feels torque more than horsepower when accelerating.

The TDI diesel has a very flat torque curve that peaks at 149 foot-pounds at merely 1,900 r.p.m. This low-end torque performance gives the New Beetle diesel quick acceleration off the line. One can even briefly squeal the tires of the front-wheel-drive car in the best hot-rod tradition.

The broad torque range allows for good mid-range performance; the gasoline-engine model is faster at highway speeds, but the diesel model provides good 65-75 m.p.h. passing times. It also easily cruises all day at typical highway speeds.

However, the New Beetle diesel is best suited to the fairly slick manual, because the automatic stifles performance a bit. The automatic isn't available yet, but half the New Beetle diesel buyers are expected to order it, said Volkswagen of America spokeswoman Maureen Terry-Morehead.

Finding diesel fuel should be no problem, because Mercedes-Benz diesel models have been sold throughout the country for decades. Volkswagen also has sold many diesel autos here.

The New Beetle gasoline model is virtually identical to the diesel version except for the engine. The car has smooth retro styling with a very long dashboard. The front seat area is roomy, but the backseat is tight and the trunk is small. The well-equipped, solidly built car has the revamped 1999 Volkswagen Golf platform, so it handles well and has a smooth ride--although some bumps jolt occupants.

The steering is rather vague at the on-center wheel position but can be made sharper by increasing front tire pressures by six pounds over factory recommended pressures. Braking is good, and the New Beetle diesel model I drove didn't have the overly sensitive brake pedal that was in the New Beetle gasoline model I tested.

Controls for the power windows are a pain; they're flush on the door and call for an unnatural twist of a wrist to operate. And tiny sun visors are useless for blocking sun from the side.