After driving the BMW 335d the other day, I noted that if I hadn't known better, I would have thought I was sitting behind an ordinary gasoline engine. Listening to the Mercedes-Benz E320 Bluetec, it's hard to discern whether there's any engine. Even when I lead-footed the car around the David Zenlea Winter Proving Ground - aka: the snow-covered parking lot near my apartment - I could scarcely hear anything other than the subdued hum of the HVAC.
Mercedes clearly has the refinement issue down when it comes to diesels. Unfortunately, it's not quite as far along in terms of driving engagement. Whereas the BMW diesel uses dual-stage turbocharging to provide smooth, instant power delivery, the single-turbo setup in the E320 seems to suffer from a bit of lag. To be fair, the combination of icy roads and an eager stability control system can make any car feel like a laggard, and once it gets off the line, there is plenty of grunt. But even with stability control disabled, the E320 was not all that excitable. Mercedes does have a bi-turbo setup in its newest four-cylinder diesels, and west coast editor Jason Cammisa is already singing its praises. Alas, we will not see it in the United States. I spoke with Mercedes powertrain vice-president Dr. Leopold Mikulic during the Detroit show, and he indicated the company would likely be sticking with the single-turbo V-6 diesels for the U.S. market. That's a shame, especially since the smaller engine would also provide better fuel economy. As it is, it's hard to get worked up about 23/32-mpg city/highway numbers.
Still, the E320 is a compelling, comfortable package, and there's little reason a non-performance-oriented buyer shouldn't go for the diesel. The new model coming for 2010 should be even better.
David Zenlea, Assistant Editor