Chevrolet's Cruze diesel is hugely important.

It's the first to challenge Volkswagen's lock on the mainstream diesel market.

It's coming from the company that — never mind who did what to the electric car — still gets plenty of blame for killing the diesel in the U.S. Something about those really bad ones in Oldsmobiles during the 1980s fuel crisis.

And it's a purebred GM diesel engine, on sale overseas for several years, though heavily modified for U.S. regulations and tastes.

In a fell swoop it'll show whether American buyers are as diesel-averse as most of Detroit has assumed or as diesel-ready as VW's always found them.

And the Cruze diesel will test GM and Chevrolet marketing savvy and muscle. It's just now on sale, but only in 13 cities, and won't go national until fall. Can the marketeers give it enough traction to survive a VW response (discounts, advertising, etc.) and the buzz generated by the launch of the Mazda6 diesel this summer?

If Cruze diesel succeeds, it's bound to kick off copycat models from other makers. A flop could set back the move to fuel-saving diesels in the U.S. by quite a bit.

Overall, the Cruze's mating of a powerful and fuel-saving diesel to a good compact sedan is a happy marriage. But not a cheap one.

Chevrolet's Cruze diesel, a 2014 model, carries a significant price premium over gasoline models. The diesel's $2,560 more than the most-similar gas model, the 2LT. And it's $4,010 more than high-mpg Cruze Eco, from which it takes a few aerodynamic-enhancing parts.

Yeah, you say, but it's a diesel; uses hardly any fuel, right?

Not exactly. The diesel's highway rating is 46 mpg, the best in the U.S. for a non-hybrid, and a good bit better than the gasoline models' 38 and 39 mpg highway ratings.

But most people spend more time in the city or in a mix of city/highway driving. And there, the diesel's not much better than the gas models: just 27 mpg in the city, vs. 26 for the gas cars. And 33 in combined city/highway, no huge win over gas 30 and 31 mpg ratings.

So, unless you roll up open-road miles like Willy Loman, the diesel's 46 mpg won't be as compelling.

Diesels typically stand out on the highway, but other diesels outdo their gas counterparts in the other driving modes somewhat more handily than Cruze does.

Nor is the Cruze diesel a slam-dunk vs. its only rival, the Volkswagen Jetta diesel. Jetta with an automatic transmission is slightly more expensive than Cruze, which comes only with an automatic. Jetta with a manual, however, is slightly less expensive.

Too, Jetta has more rear legroom, a bigger trunk and — probably, most important — better city (30 mpg) and combined city/highway (34 mpg) ratings than Cruze diesel.

It'll be hard to justify buying a Cruze diesel solely on fuel-cost savings. But there's enough "happy" to save this marriage:

Scoot. Chevy notes that the diesel is the quickest Cruze. It'll dash from standstill to 60 mph in 8.6 seconds. That's on the edge of feeling peppy enough to be fun on the road. Gasoline Cruzes are slower, taking as long as 10 seconds, Chevrolet says. Diesel wins the dash even though it's 320 to 464 pounds heavier than the gasoline models. Remarkable.

Diesels are powerful but tend to take a moment to get their "go" in gear. Cruze seems to have gotten past that — but apparently at the expense of fuel economy.