Diesels: What's all the clatter about?

0707 490 Fp Diesel Feature

What's all this clatter about diesels lately?

Why now? Why twenty years after we, as a country, have lost interest in the slow, smoky Mercedes and Volkswagens that became synonymous with Diesel power? You can thank your government.

See, for years, residents living in countries with less than fifty states have been enjoying the fuel economy benefit of diesel passenger cars - they consume on average about thirty percent less than comparably powerful gasoline models - while we lumbered along in our thirsty, gasoline-powered SUVs. The reason we didn't get the miserly diesels is simple: the quality of the diesel fuel available in this country was too poor to run the new engines on.

The new-technology diesel engines operate quietly and efficiently by injecting the fuel into the cylinders at ungodly high pressures through teensy nozzles. A high concentration of sulfur, which must otherwise be refined out of the diesel fuel, clogs those injectors.

For years, automakers and fuel companies have been stuck in a "you first!" battle like something you remember from grade school. "You refine the diesel fuel first, and we'll bring the good engines in!" "No! You bring in the engines first, and then we'll supply fuel for them! You first!" "No, you!"

Beginning in 2006, though, new regulations required that the fuel companies supply ultra-low sulfur diesel to the public. (Just in time, as it turned out, for the few remaining diesel passenger cars on the market to no longer be able to satisfy emissions regulations - but that's another story). And so the floodgate opens, letting all the diesels in.

Aren't diesels slow?

How about this for an answer: I lost a race in the new 414-hp, V-8 M3 last week to a diesel. I pulled up to a red light next to my photographer's six-cylinder, automatic-transmission 530d station wagon. When the light turned green, I dumped the clutch from 2000 rpm and floored it. And the automatic diesel station wagon dusted my M3 off the line. I didn't catch up until 60 mph.

Are diesels slow? That's the same thing as asking if gasoline-powered cars are fast: Some are, some aren't. Today, diesels make just as much power as comparably sized normally aspirated gas engines. Diesels make loads more torque, though, so they feel even faster than they are.

Don't diesels smoke?

Not any more. Smoke coming from a diesel engine is partially unburned fuel, and the new engines run so efficiently they make sure there's no waste.

Aren't diesels hard to start in the winter?

Not any more. Well, to a point. Modern diesels don't use glow plugs the way the old ones did - at temperatures above, say, 50F, they start normally. In temperatures below that point, they may take a couple of seconds extra to start - but not the minutes the old ones took.

The caveat is that diesel fuel turns into a Jell-O-like substance when it gets very cold. Modern fuels are treated with anti-gelling agents to prevent this, but they only work until a point. That point, however, is usually somewhere on the shivery side of -20F. So unless you live somewhere where it's regularly colder than that, you needn't worry.

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