Mercedes-Benz has long been a proponent of diesel engines, and the current Bluetec is so good that its quiet performance and good fuel economy are sure to win over customers.

This 3.0-liter diesel V-6 is available in the E-class sedan, the M-Class SUV and the R-Class people mover. The ML320 diesel has a base price of $44,455.

Many folks think of diesel engines as loud, sooty and crude, but today's high-tech diesels are clean, quiet and 20 percent to 40 percent more efficient than gasoline engines. They also emit less carbon monoxide and carbon dioxide. With the Bluetec technology, nitrogen oxide is reduced with two additional catalytic converters. Mercedes-Benz says the E320 Bluetec is the cleanest diesel in the world.

Currently, the engine is not available in California, Maine, Massachusetts, New York and Vermont because it doesn't meet the stricter emission standards of those states.

Bluetec is a term you'll be hearing more and more because Audi and Volkswagen have adopted the technology for their diesels as well. Diesels are so popular in Europe that more than half of all vehicles are so equipped.

The ML320 CDI is a great example of why diesels make so much sense, especially in a vehicle whose utility requires a boxy profile. The diesel's fuel economy ratings are 21 city and 27 highway, compared to 17 city and 21 highway for the gasoline engine in the ML350. Those figures give the ML a cruising range of 600 miles on a tank of fuel.

The ML's diesel produces 215 horsepower and 398 pound-feet of torque. That's considerably more torque than the V-8 in the ML500, and it comes at least 1,000 rpm sooner. That makes the diesel a perfect partner for towing or hauling heavy loads.

The V-6 has four valves per cylinder, dual overhead camshafts and piezo fuel injectors that spray fuel directly into the center of each cylinder. A variable-nozzle turbocharger adds power and a counter-rotating balance shaft reduces vibration. The engine is mated to a seven-speed automatic transmission, and full-throttle acceleration feels stronger than that of the gasoline engine.

European diesels are increasingly available in this country because recent changes in government regulations mandate low-sulfur diesel fuel.

Mercedes claims that its diesel is more fuel-efficient than a comparably sized hybrid vehicle. In a cross-country test, the German magazine Auto Bild compared an ML320 diesel and a Lexus RX400h hybrid. The ML used 11 percent less fuel.

Another advantage of a diesel engine is its ability to burn biodiesel, made from vegetable oils, and biomass-to-liquid diesel fuel. BTL fuel can be made from any biomass, including scrap wood.

The second-generation ML has a 114.7-inch wheelbase that is 3.7 inches longer than the previous model's. Overall length is up by 5.9 inches and width is up by 2.8 inches. The new truck sits about a half-inch lower.

The ML's ride is smooth without being mushy, yet it is able to handle moderate off-road conditions easily.

The ML is more refined across the board. The cabin, and especially the instrument panel, looks more like that of a sports sedan than a truck. Large, tubular air vents exit from the top of the center stack. The center console has two large cup holders, integrated grab handles and an armrest with storage.

The four-wheel-drive system combines full-time drive to all four wheels with four-wheel traction control and a low range. Under normal driving conditions, torque is split 50-50 between the front and rear wheels. When conditions demand, torque is transferred to the wheels with the most traction. Antilock brakes, traction control and a vehicle stability program are standard.

The longer wheelbase results in more interior space. Front legroom has been increased by 2 inches, while rear-passenger legroom is up by 1.3 inches.

The split-folding rear seat flips forward without requiring removal of the rear-seat headrests. Total cargo space is 72.4 cubic feet with the seat down. The cargo area is finished with nice carpet. A power liftgate is optional.

Price The base price of the test car was $44,455. Options on the test car included leather seats, six-disc CD changer, rear parking sensors, metallic paint and the premium package that includes the navigation system with backup camera. The sticker price was $57,375.

Warranty Four years or 50,000 miles.