2014 Audi A6 TDIEnlarge Photo
In low-speed stop-and-go driving, however, even modern-day diesel engines are no revelation in efficiency, sipping away at their fuel at a less frugal rate. It's where we’ve noticed, for instance, that a Volkswagen Jetta Hybrid will surge ahead of a Jetta TDI in real-world fuel-efficiency, for example, even if the TDI is better in most real-world highway and combined conditions. And that’s where engine stop-start technology chimes in as an odd—but surprisingly effective—companion for diesels.
We haven’t, up until this year, seen start-top with a diesel engine in the U.S. market, but in the blink of a model year it's suddenly de rigueur.
A tipping point for the technology...if you're shopping luxury brands
The technology, already proven in Europe—and of course, in a different form, in many hybrid models—has reached a sort of tipping point, such that it isn’t just being cautiously introduced by a single automaker; nearly all of the new diesels offered by luxury brands will soon have stop-start, and every single diesel introduced this fall in a luxury vehicle has it. That includes the BMW 328d sport sedan, the Mercedes-Benz E250 Bluetec, and the new TDI versions of the Audi A6 and A8 sedans, A7 hatchback, and Q5 crossover.