Tons o' Torque

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"During the 1980s, one of the major objections to compression-ignition engines was noise. Sooty smoke and that peculiar exhaust aroma — call it eau de diesel — were also problems, but it was the noise that really turned heads. We were highly aware of these things at the time because then, as now, fuel economy was a major concern, and, as now, diesels seemed to be an answer.

A lot has changed since then. For one, the big concern of those energy-crisis times was the availability of fuel — remember those lines at the pump? — rather than its price. More important, soot, odor, and clatter have been removed from today’s passenger-car diesels. And this Mercedes ML’s new 3.0-liter V-6 turbo-diesel is a compelling case for quiet. Aside from a hint of rattle at startup, it’s quiet across its entire power band. For contrast, the ML350 we tested in June 2005 blipped our sound meter to 43 dBA at idle and 71 dBA at full throttle. This ML320 came in at 42 and 69, respectively.



These noise distinctions seem very close, but remember that the decibel scale is logarithmic; the steps are steep. Think of the difference between having the London Philharmonic playing on your patio, then moving into the living room. It ain’t subtle



Although new to the U.S. market, this engine has been available in Europe since early ’05, offered in a number of different Benzes: C-, E-, and R-classes, as well as M. It’s a DOHC 24-valve 72-degree V-6, rather than the classic 60-degree layout, a design dictated by packaging considerations, and it uses a balance shaft to quell primary vibrations. Like all the latest automotive diesels, the V-6 is fed by a common-rail fuel system, whose mind-boggling line pressures — this one tops out at 1600 bar or 23,200 psi — create the fuel atomization required for complete combustion. The direct injection employs a single eight-orifice piezoelectric injector in each cylinder, delivering between two and five spritzes per power stroke, one of the keys to the engine’s quiet operation. It’s also clean — not a trace of soot in the tailpipe — although at this point it’s legal in only 45 states.
The Garrett turbocharger, blowing through a Behr air-to-liquid intercooler, pumps up combustion-chamber pressure, with max boost listed at 1.45 bar or 21.0 psi. Peak horsepower is a modest 215 at 3800 rpm, but diesels are all about torque, and there’s plenty of that: 398 pound-feet between 1400 and 2800 rpm, which is more than that of the 5.0-liter gas V-8 in the ML500. That’s enough to get this 2.5-ton luxury SUV — 239 pounds heavier than the ML350 — to 60 mph in 8.1 seconds, a second slower than the 268-hp gasoline version.



Of course, diesels are also about fuel economy, and on this issue the jury’s out. Mercedes talks about going from Detroit to New York — 639 miles — on one 25.1-gallon tank, but at the consumption rate we observed — 19 mpg — you’d wind up walking the last 162 miles. However, we were constrained by availability of ultra-low-sulfur fuel — required for the Benz’s particulate filters — at the time of our test, so most of our driving was local, hasty, and urban.



Even so, 19 is 2 mpg better than we achieved with the ML350. And it’s also worth noting that our man Gillies recorded more than 28 mpg driving an identical ML320 CDI in the U.K. last summer.

The Highs: Extraordinarily quiet, tons o’ torque, super-smooth seven-speed transmission, smokeless exhaust.

The Lows: “Comand” confusion, never-quite-right damping adjustment, porky curb weight, disappointing MPG.

But one thing is certain: You’ll never hear this one coming."

Specifications

VEHICLE TYPE: front-engine, 4-wheel-drive, 5-passenger, 5-door wagon
PRICE AS TESTED: $58,825 (base price: $44,455)
ENGINE TYPE: turbocharged and intercooled DOHC 24-valve diesel V-6, aluminum block and heads, direct fuel injection
Displacement: 182 cu in, 2987cc
Power (SAE net): 215 bhp @ 3800 rpm
Torque (SAE net): 398 lb-ft @ 1400 rpm

TRANSMISSION:
7-speed automatic with manumatic shifting

DIMENSIONS:
Wheelbase: 114.8 in
Length: 188.5 in
Width: 75.2 in
Height: 70.0 in
Curb weight: 5041 lb

C/D TEST RESULTS:
Zero to 60 mph: 8.1 sec
Zero to 100 mph: 23.8 sec
Street start, 5–60 mph: 8.7 sec
Standing ¼-mile: 16.3 sec @ 85 mph
Top speed (drag limited): 132 mph
Braking, 70–0 mph: 176 ft
Roadholding, 300-ft-dia skidpad*: 0.78 g
FUEL ECONOMY:
EPA city driving: 18 mpg
C/D-observed: 19 mpg
*Stability control inhibited.

Overall a good review.

I've personally driven the ML320 CDI and the ML350 and I'd take the diesel over the gasoline V6 anyday anytime. You get virtually the same performance but better fuel economy. I've also noticed that the ML320 CDI is a pretty quiet ride.

I'm surprised they were a little dissapointed with the fuel economy. But it's probably due to American-spec Mercedes' getting different final drive ratios that are biased towards acceleration and sacrifice fuel economy for that.

I would also take the 320 CDI over the 350. What may interest you is that my uncle recently purchased an ML320 CDI, it replaced his last generation ML500. He thinks it was a great trade, i happen to think so too.

Good to hear.

I'd love to own an M-Class and especially an ML320 CDI which IMO is the best allround M-Class hands down. The ML280 CDI is a little sluggish and the ML350 and ML500 guzzle too much gas. The ML63 AMG is an awesome car - and the performance is mindblowing, but I consider it a rather pointless vehicle.

It is awesome and but as you said, it's rather pointless. I love the ML63, in fact i'd rather have it over a Cayenne Turbo but the fuel consumption is terrifying. In all honestly, and in my opinion of course, if you want a "peformance SUV" the Audi Q7 V12 TDi is the best bet. While still a little pointless it does have the advantage of better gas mileage.

To me, the performance of the ML320 CDI or Q7 3.0 TDI etc. will be more than adequate.

I consider the Q7 V12 TDI to be in the same league as the ML63 AMG: pointless. Of course, Audi is trying to do something cool with diesels because of those Le Mans victories with their diesel racecar.

Having a bit of seat time in the MLcdi I can say it is a delight to drive. I'm very confused about the fuel mileage recorded by C&D. 19 is the low end of the rating. this thing is rated 27 on the highway. It's not unusual for most to squeeze out a couple of gallons above the top rating in a Benz. for example i commonly have owners tell me they are getting 23 in the ML350 on interstate driving. If this truck can't consistently average above 22, then I would not pay the premium on the sticker of $1,000 and the .40 each time at the pump. diesel is way pricier here compared to regular fuel. go figure?

Update.
Our company demo is averaging 19.5 mpg. This is over 224 miles and with only an average speed of 20 mph. Obviously stop and go driving. The ML350 would be luckly to do 15 in same situation. I'll be curious to see how some extending highway driving will turn out.

Interesting information, thanks.

When I had a summer job at Mercedes a year ago, there was a week where I got drive around and do deliveries in an ML350 all the time. After the excitement of the first few days of driving it had calmed down, I was babying it on country roads and driving it as fuel efficient as possible. It still drank a lot of gas.

When it comes to SUV's, there is only one engine choice for me: diesel.