Honda reworks Acura into fuel-efficient diesel

Honda has spent decades establishing a reputation for fuel efficiency. But nothing in its current lineup, including its Civic Hybrid, can match the mileage of the diesel Accord I recently tested in and around New York City.

Minus its diesel powertrain, the European-market 2007 Accord that I drove is nearly identical to the car that Honda had been selling in the United States as the Acura TSX (in other words, it's smaller than the American Accord). The test car should give a solid indication of the mileage and performance American consumers can expect when Honda offers a diesel option for the redesigned 2009 TSX.

The Accord — a demonstration car provided by Robert Bosch, the German technology company, to highlight its fuel injectors and other diesel components — returned a remarkable 53 miles a gallon on the highway, 34 in the city and 44 in combined driving. Those miles included a bumper-to-bumper crawl through Manhattan, the worst possible conditions for fuel efficiency.

Cleaner emissions system

The model I drove was powered by a 4-cylinder diesel displacing 2.2 liters and producing 140 horsepower and a stout 250 pound-feet of torque — the force that drivers feel pushing them into their seats under acceleration. That huge torque relative to the engine's size is a main advantage of modern turbodiesels, making them well-suited to small economy cars and to burly SUV's that need torque for towing and hauling.

The America-bound Acura will use a new version of the 2.2-liter engine that I tested. The engine is notable for meeting 50-state emissions standards with no need to carry an onboard tank of urea, an ammonia-generating solution that other diesels use to scrub smoggy nitrogen oxides from the exhaust. Honda's patented pollution system generates its own ammonia to fulfill the same mission. While that cleaner emissions system wasn't installed on the Honda I tested, engineers expect it to have no discernible effect on fuel economy.

Advantages over hybrids

As with other diesels I've driven recently, the Honda's frugal highway mileage and versatile power are important advantages over the typical hybrid. The Accord covered the zero-to-60 run in just under 9 seconds in my testing, which doesn't sound spectacular on paper. But its passing power from 30, 50 or even 70 miles an hour was terrific, as the Honda easily shot past slower cars.

And as more hybrid owners are discovering, their cars deliver little or no mileage gain on the highway. That's because battery packs and electric motors add several hundred pounds, and the system also contributes negligible energy at freeway speeds.

Also unlike hybrids, which require drivers to go easy on the gas pedal, watch the speed limit and coast when possible to improve the mileage, the diesel Honda delivered brilliant economy with no special effort. Even spirited driving didn't dent the mileage much. The Accord delivered 50 mpg even during a 75-mph cruise and 40 mpg when I flogged it.

The Acura's only diesel telltale is an idle that's slightly louder than a gasoline car's, though it's not at all obtrusive. There was no trace of diesel smell or black exhaust.