Why Are Some Diesels Illegal?

Euro-diesels are very efficient, burning less fuel and therefore putting out less carbon dioxide, a greenhouse gas. The problem is NOx (which produces smog,) and particulate matter (which emits carcinogenic particles.)
Read: Guide to Diesel Vehicles

If you crave high gas mileage but aren’t a stickler about low emissions, then a European diesel-powered car will beat out a hybrid any day. The only problem: They are illegal in the US.

That’s mostly because Europe’s high-mpg diesels lack the sophisticated and pricey after-treatment systems required to meet the latest US emissions standards. And carmakers have been unwilling to make them legal by passing emission and safety regulations, and marketing cars that are small but relatively expensive.

Ever since the Ford Fiesta’s unveiling at the British International Motor Show in July 2008, we’ve been eager to get a close look at the sporty subcompact five-seater—the most fuel-efficient car available in the UK.

Ford Fiesta ECOnetic – 65 MPG

Ford achieved the impressive 65-mpg via aerodynamic body styling, lowered suspension, and low resistance tires. Extensive use of high strength steels and a focus on cutting weight also reduced the mass of the new Fiesta—despite improved safety equipment and sound insulation.

We’ll have to wait to get behind the wheel of the Fiesta diesel, but we did get our hands on a 2007 Audi A6 TDI and a 2006 Smart ForTwo CDI for the weekend. We took the A6 for a 500-mile high-speed joy ride through the fields and hills of upstate New York. How was the fuel efficiency? 39 miles per gallon—impressive for a midsize luxury sports sedan with crisp styling, lots of electronic frills, and the torque of a freight train.

Audi A6 TDi – 39 MPG

The big A6 diesel was a delight to fling around the two-lane country roads between Woodstock and Ithaca. The Quattro all-wheel-drive kept the car firmly on line through corners despite spirited driving—and the car tracked straight regardless of speed, road surface, or side winds. Noise isn’t an issue; inside the Audi, you’d barely know it’s an oil burner. Outside, the idling is deeper and clankier, but it’s nowhere near the garbage truck rattle of older diesels.

Smart ForTwo Brabus CDI – 71 MPG

Smart ForTwo Brabus CDI

We were less impressed with another Euro-diesel we tested—despite the 71 mpg promised by Smart. The 2006 Smart ForTwo Brabus CDI is a semi-hot-rodded version of the standard diesel Smart sold in Europe. It had a number of nice upgrades over the standard Smart—a glass roof, leather seats, even an aero kit—but the Brabus CDI just crept away from stoplights before the turbo spooled up to boot it forward. We had to “row” the car with the paddle shifters—fun and sporty if you’re up for it, but tedious for hours of city driving. Unfortunately, our short tenure with the Smart didn’t let us test mileage, but hopefully it delivers as promised because the tank holds only 6 gallons.

Our wish list of high-mpg contraband includes these three 60-plus-mpg machines that put US hybrids to shame in the fuel efficiency department. If it weren’t for the problem of diesel emissions…

SEAT Ibiza Ecomotive – 62 MPG

SEAT Ibiza Ecomotive

In late 2007, Spanish automaker SEAT, a subsidiary of Volkswagen, introduced the Ibiza Ecomotive, its most economical, least polluting production model to date. The SEAT Ibiza has adequate pep, hitting 60 mph in 12.8 seconds. The particulate filter and an exhaust gas recirculation system make the Ibiza one of the cleanest-running cars on sale in Europe—still not good enough for US standards.

Volkswagen Polo BlueMotion – 62 mpg

Volkswagen Polo BlueMotion

In 2006, VW introduced the Polo Bluemotion, which uses a modified version of the 3-cylinder 1.4-liter TDI diesel engine to produce the same power output found in the conventional Polo—but with increased fuel efficiency to about 60 mpg. In the most recent release, Volkswagen managed to squeeze out an additional 2 mpg, by optimizing the engine and fine-tuning the aerodynamics. With the better fuel efficiency, the Polo BlueMotion’s CO2 emissions dropped to 99 g/km. Its 0 – 60 performance matches that of the SEAT Ibiza.

MINI Cooper D – 60+ mpg

MINI Cooper D

The diesel-powered MINI Cooper D forces the other fuel-sipping diesels to the slow lane. This car can hit 60 mph in less than 10 seconds, while maintaining the US equivalent between 60 and 70 mpg. Automotive News, the trade publication, managed 74-mpg on their test run. This car also uses stop-start technology to shut down the engine when it comes to a stop. With its cute looks, zippy performance, and great handling, the MINI Cooper D would be a winner in America, but BMW would have to use more advanced emissions controls to bring it to all 50 states in the US.