It's good news that more automakers are willing to gamble on fuel-efficient diesels in the historically anti-diesel U.S. market.

But it's bad timing that the rollouts are beginning now, when diesel fuel prices are up — wiping out diesel engines'
20% to 40% edge in fuel efficiency.

But fuel prices fluctuate, and high-mileage diesels might again seem like salvation. In which case, it'll be important to
remember that not all diesels are equal.

For instance, the BMW 335d diesel sedan is terrific. The Mercedes-Benz ML320 diesel SUV evaluated this week isn't.

The ML that seemed much-improved when redesigned for 2006 competes in a crossover SUV market flooded by newer,
better rivals: Honda Pilot, Ford Edge and Flex, Toyota Venza, Mazda CX-9, Hyundai Veracruz, etc.
Against those, the ML seems a bit sad and tired.

So M-B buffed the ML SUVs for '09. In addition to adding the diesel: new bumpers and headlights, modified grille,
bigger mirrors and updated door panels and seats.

The BlueTec diesel lets you start from a stoplight smoothly, or quickly, but not both.
Light on the throttle, it creeps. Heavy, and the vehicle lurches forward. You get what you want, but not how you want it.

Same once underway. Nail the throttle, and the vehicle jerks, lurches and responds. If you don't expect an emergency,
or an acceleration challenge such as passing and merging, you may not mind.

In a way, it's not unexpected. The seven-speed automatic transmission M-B uses widely has had lurch-and-jerk issues.

The diesel engine itself probably is fine — a little shy on horsepower, perhaps, but torque-rich as diesels are.
How it interacts with the transmission, though, is unpleasant.

M-B thinks these remarks are off-base. The diesel's torque is available at a mere 1,600 rpm, M-B says, so of course
you get a big reaction with a push on the throttle. M-B insists that everybody else thinks its a smooth setup.

M-B, in fact, disputes about every gripe. The gripes are serious, so it's appropriate to give them a word.

M-B has soldiered through the past few years with a diesel popular in much of the U.S. but illegal to sell in
California and a handful of other states with super-stringent pollution laws. Now, federal clean-air rules are as
tough, and automakers have developed diesels that can be sold everywhere.

M-B called the previous diesel CDI. The new one — a modified version — is BlueTec. It pollutes less, largely because,
as common in today's 50-state diesels, urea carried in a small tank is injected into the exhaust stream to chemically
cut oxides of nitrogen, a pollutant that's been hard to exorcise from diesel exhaust.
The dealer refills the urea (aka AdBlue) tank at oil changes, but unlike BMW, M-B charges for oil changes.

So let's raise a cuppa to BMW, M-B and Volkswagen for leading the way with diesels in the U.S.

But let's also shake our heads in dismay that M-B, which invented the automobile and pioneered the diesel car
70 years ago, hasn't yet perfected cars or diesels.

In addition to the herky-jerky drivetrain, more came to light in a week tooling around the burbs:

•Mediocre mileage. The test vehicle's 19 miles per gallon was close to the window-sticker estimate but also
matched by Chrysler's Aspen/Dodge Durango hybrid SUVs.

Those burn cheaper gasoline, have more room inside, offer three rows of seats instead of two and are priced
about $4,000 less. But, sadly, they're out of production on Dec. 23 09 because Chrysler can't afford the Delaware
factory that makes them.

•Terrible ride. Bumpy and jiggly on even the smoothest pavement. Surmounting a branch felt like a major dynamic
event. The tester had three suspension settings: comfort, normal and sport — all poor. Perversely, it nonchalantly
swallowed big bumps such as drainage channels at intersections.

Maybe the switch to 19-inch wheels and tires from the previous 17s hurt a little, M-B says, but even so, everyone
else seems to think the normal setting is just right.

•Lagging brakes. Push, push, push the brake pedal and just when you think something's amiss, the brakes start
to haul it down. Let off the pedal, and the brakes continue slowing it a moment.

That's how M-B electronic brakes have behaved. But M-B says ML has a conventional hydraulic system that simply
can't behave that way. And, it says, "We've been praised for our braking performance in the ML320."

•Hard seats. Not firm. Not stiff. Not you'll-get-used-to-it Teutonic. Hard. Like a board, or slab of concrete.
And trim popped loose from the driver's seat sliding track. Popped back on easily, but still …

No way, M-B argues, seats are one of the best features.

•Subpar details. For instance, climate control was too hot at 70 degrees, too chilly at 68.

Optional video screens were perched on the back of each front seat, not built into the head restraints, not
color-matched nor integrated in any apparent way. Yeah, but the video's now an $1,850 option instead of
$3,100 when screens were in the head restraints, M-B points out.

The navigation system, typical of high-end German vehicles, didn't list enough street names.
All the streets are shown, but only a few are named.
The BMW tested last week had the same drawback.

On the plus side:

•Controls — save for the Comand master-control knob — had a luxury feel.

•Dashboard keypad has 10 digits, so you can select 10 radio stations without clicking a menu.

And, uh … well, that's where the celebratory notes end.

Fifty thousand US bucks for an uncomfortable, not-so-classy machine that's unpleasant and unsatisfying to drive.
Wonder who signed off on that business plan?

About the Mercedes-Benz ML320 BlueTec diesel SUV

•What? Diesel-power version of midsize, four-door, five-passenger, crossover SUV. BlueTec is Mercedes-Benz's
name for clean-air diesel that meets pollution standards in all 50 states and Washington, D.C. Previous ML diesel
wasn't legal to sell in California and Northeast states that copy California emissions regulations.

•Why? One-fourth of M-B SUVs have diesels in some U.S. markets. Should rise now that the diesel's also legal in
California, as well as in New York and other states that copy California's pollution rules.

•How powerful? 3-liter V-6 diesel is rated 210 horsepower at 3,400 rpm, 398 pounds-feet at 1,600 rpm,
driving through seven-speed automatic transmission with manual-shift mode and 4Matic all-wheel drive.

Same drivetrain is available in M-B's R and GL SUVs.

•How lavish? Fairly, and you can spend till the cows come home on options. 

•How big? Midsize, a couple of inches bigger than Ford Edge. ML320 diesel is 188.5 inches long, 76.3 in. wide,
71.5 in. tall, on a 114.7-in. wheelbase.

Weighs 4,974 lbs. Rated to carry 1,266 lbs. of people, cargo and vehicle accessories. Tows 5,000 lbs.

Cargo space: 29.4 cubic feet behind rear seat, 72.4 cu. ft. when seat's folded.

•How thirsty? Rated 18 miles per gallon in town, 24 on the highway, 20 in combined driving.
(3.5-liter gas V-6 rated 15/20/17.) Trip computer in tester showed 19 mpg in suburban driving.

Ultra-low-sulfur diesel required; tank holds 25.1 gallons.

•Overall:  Nope.