Dear Tom and Ray:

I own an Audi A4, and I just spent a week in Italy. I found out that more than 50 percent of the A4s sold in Europe have diesel engines. I also rode in a diesel-powered A6 and an Opel Astra. Both cars were very quiet and powerful. My friend with the Opel told me that the car starts without a delay, unlike some older diesels. So, the new diesel engines are not much different from gas engines, and they save a lot of fuel. Are we missing an advance in car design in the United States? -- Al

RAY: Well, here are the things we've always hated about diesels, Al: They're hard to start when it's cold. They clatter and make noise. They smell bad. They emit black soot out of their tailpipes. And yes, we're missing all those advances here!

TOM: Actually, modern diesels are a lot better in all of these regards, although a diesel that starts easily in Italy might not start quite as easily in Norway -- or Minnesota.

RAY: But the biggest discrepancy still is pollution. Gasoline is heavily refined before it ever gets to the pump; diesel fuel, on the other hand, is just one step removed from primordial sludge. When you pump it into your car, there are still rocks, branches and fossilized wildebeests in it. As a result of that, diesel engines spew out more particulate emissions than gasoline engines.

TOM: Europeans have traditionally demonstrated less concern about air pollution than we have here in the United States. You probably noticed that the air in Italy is a lot dirtier than your air at home. The same is true of the old men there!

RAY: And needless to say, the Europeans have never been bothered by the smell!

TOM: Apologize for that. Just do it now, before the French Embassy calls to demand a retraction.

RAY: OK -- I'm sorry.

TOM: On the other hand, the reason Europeans are so fond of diesels is that they're cheaper to run. Not only do diesels get better mileage, but the cost per gallon of diesel fuel is lower. Regular gasoline can cost $4 to $5 a gallon in Europe. So, saving 10 percent to 20 percent off a tankful is a much bigger deal there, not to mention having to fill up less often. Here, where gasoline is still cheaper than bottled water, people just don't have enough incentive to accept the diesel engine's tradeoffs -- even if those tradeoffs are diminishing.

RAY: So, what might make folks in the United States rethink their aversion to diesels? Well, if the price of gasoline keeps going up, that might increase interest.

TOM: But what would make a bigger difference is truly clean technology. New combustion technology is already being used on modern diesel engines. And there are scrubbers that exist that can reportedly clean up diesel exhaust pretty thoroughly.

RAY: Low-sulfur diesel fuel will help, too, and that's supposed to be here by late 2006, along with stricter EPA standards for diesels soon thereafter. But those improvements, in all likelihood, will increase the cost to the consumer. And cost has always been diesel's main advantage.

TOM: So until those technologies are implemented, and unless the overall cost of owning a diesel -- with those technologies -- remains meaningfully lower than owning a gas-powered car, I doubt we're going to see a huge surge of diesels here in the United States. Sadly, Al, in order to drive a diesel A4, you're going to have to plan another vacation in Italy. Poor guy!