Sherrice Gilsbach
Kids: 2 Ages: 4 & 7

Clean-diesel cars have my heart, and it’s easy to understand why: Their fuel economy is at least 30 percent better than the fuel economy of gasoline engines. From clean-diesel cars’ impressive performance to a reduced dependence on foreign oil, I’m hooked on them.

I test-drove several clean-diesel SUVs — the 2009 BMW X5 xDrive35d, 2009 Mercedes ML320 Bluetec, 2009 Audi Q7 TDI and 2010 Volkswagen Touareg V6 TDI — recently and was really impressed by these SUVs. The X5 gets an estimated 19/26 mpg city/highway and has an MSRP of $51,200, the Q7 gets 17/25 mpg and costs $51,900, the ML320 gets 18/24 mpg and costs $48,600, and the Touareg gets 17/25 mpg and costs $42,800.

As a reviewer for, I’ve been behind the wheel of plenty of SUVs, so I have a foundation for comparing one SUV to another. Regular SUVs’ gas mileage is usually underwhelming and their performance is lacking. That’s not the case with clean-diesel SUVs.

On the Road

While the cleanliness of today’s diesels will make you feel good about your purchase, their efficiency will blow your mind. I took the X5 and the Q7 on long road trips and was shocked by the incredible gas mileage from both SUVs. These SUVs are capable of achieving 600 miles on one tank of diesel. Over endless stretches of highway, through one small town after another, the gas gauges on the X5 and Q7 didn’t budge. Even when I used the air conditioning, which usually guzzles fuel, we were surprised by the cars’ minimal fuel consumption.

From a performance perspective, I found the Q7 to be my clean-diesel match. The Q7 can seat five, six or seven passengers, but despite its size it has ample power. It accelerated quickly and easily from a stop. The ML320 and X5 struggled to take off quickly from a stop; I find that most SUVs have this problem regardless of their type of fuel. All of my test diesels, however, kept up with highway traffic and showed no hesitation when passing other cars on the highway.

Debunking Diesel Myths

Diesels are loud: While a diesel engine does emit a distinctly different sound than a gas engine, it’s in no way overwhelming or obnoxious. Each automaker’s clean-diesel SUV sounds different (click to hear the ML320’s, X5 and Q7’s engines; some include more sound-dampening insulators, while others want to give the engine’s throaty sound more prominence. I found the Q7 to be the quietest.

Diesels are stinky: The sulfur odor of older diesel cars has been eliminated with the introduction of ultra-low-sulfur diesel. This is combined with an advanced exhaust system that eliminates any remaining odor. When filling up my diesel test cars, I occasionally got a little diesel fuel on my hands. Surprisingly, these droplets of diesel had no odor. That’s not the case when I spill some regular gasoline on my hands.

Diesels are dirty: Forget the black smoke that older diesel cars and trucks used to belch from their tailpipes. The exhaust from clean-diesel cars is often cleaner than the air that’s sucked into the engine. According to tests by the EPA, clean-diesel cars have reduced their emissions and particulates to nearly zero.

Diesel’s Next Step

Clean diesels offer more than great gas mileage. Diesel engines are also known for their durability. Does driving get any better than that? It could in the future, according to Lars Ullrich, marketing director for Bosch Diesel Systems of North America.

The next step for diesel fuel is to make biodiesel available to the masses, Ullrich said. Second-generation renewable (or biodiesel) fuels, which will soon be available, could be used to further enhance performance and reduce emissions of clean-diesel vehicles.  Right now, the only biofuel you are likely to find in wide distribution in the US is ethanol-based.