Mercedes Diesel Does It

TRAVERSE CITY, MI – As I usually drive a hybrid to the Management Briefing Seminars, I jumped at the chance to pilot a highway-friendly diesel for this year’s journey.

It helped it was a diesel with a Mercedes body wrapped around it.

The ’14 M-Class with Mercedes’ 3.0L turbodiesel “BlueTec” V-6 proved to be a great ride here, although heavier than normal northbound traffic for a Sunday limited the length of any one test.

I put the ML350 through the fuel-economy gauntlet. I wasn’t as methodical as my dear friend and hypermiler Wayne Gerdes, but hey, it was a lazy Sunday afternoon.

I started my testing at the most extreme end, setting cruise control to 80 mph (129 km/h). My radio was on, and I had the air-conditioning set at 66° F (19° C), with three out of seven bars of fan speed.

It was a beautiful, sunny afternoon, with an outside temperature of 80° F (27° C). The temp fluctuated between the low- and mid-80s for most of my journey north.

Editor's 247-mile (397 km) trip to Traverse City yields impressive 28.6 mpg (8.2 L/100 km).

I zeroed out one of the M-Class’ trip computers on 1-75 just north of Clarkston and hoped I could last 20 miles (32 km) without hitting the brakes.

Dream denied.

I made it 19 miles (31 km) before I had to brake at the I-75/I-475 split near Flint, but I still managed to rack up great numbers.

The first leg at 80 mph averaged 27.3 mpg (8.6 L/100 km), just south of the 28-mpg (8.4 L/100 km) highway rating per EPA testing.

For my next leg, I zeroed out again and set the cruise at 75 mph (121 km/h).

I forgot about the ongoing roadwork on the Zilwaukee Bridge, so I fell 4 miles (6.4 km) shy of 19 miles before I had to hit the brakes to take the I-675 detour in Saginaw.

After an hour’s rest and relaxation in Bay City, I tried again to do the 75-mph test, and again I failed.

“Get over, get over, get over!” was my frequent cry to vehicles ahead of me on this leg, as only two lanes left me little wiggle room to maintain my speed.

Freezing by this point, I adjusted the AC up to 70° F (21° C) and reset my trip. But after a meager 12 miles (19 km), once more I was stymied by construction, the season that lasts longer than winter in Michigan.

Hilly Terrain Hurting MPG

The third time was the charm, though, as I finally got 19 miles under my belt around West Branch.

The scenic, hilly terrain of Northern Michigan proved a negative as I averaged just 27.0 mpg (8.7 L/100 km). Flatter topography likely would have returned better, not worse, fuel economy than the 80-mph leg.

At this point in my journey, I’d traveled 162 miles (261 km) from when I picked up the M-Class at the office Saturday night, with an average speed of 59 mph (95 km/h) and an average fuel economy of 27.3 mpg.

My last apples-to-apples test was at 70 mph (113 km/h) somewhere north of West Branch and south of Grayling. The terrain still is hilly, but the ML350 nevertheless returned a fantastic 32.2 mpg (7.3 L/100 km).

My goal was to do another 19 miles at 65 mph (105 km/h), but by this point I was on M-72 out of Grayling heading to Kalkaska, where posted speeds are lower, and stoplights and intersections along the route impede steady cruising.

But I did zero out again, as I knew I’d be staying between 50 and 60 mph (80 and 97 km/h) all the way to town. After 41 miles (66 km), I averaged an unbelievable 35.1 mpg (6.7 L/100 km), at an average speed of 52 mph (84 km/h).

My fuel economy from Saturday night onward was 28.6 mpg (8.2 L/100 km), better than the 23-mpg (10.2 L/100 km) EPA combined figure, but of course skewed toward highway driving.

Comfortable and Quiet

The ML350 BlueTec proved to be comfortable and reasonably quiet. Seats are nicely bolstered along the sides and, with the optional adjustable suspension set on Comfort, bumps in the road are erased. A brief moment in Sport reveals a jittery ride, as every crack and crevice could be felt.

The 3.0L turbodiesel V-6 is stellar: no clatter, no smell, although with a bit of turbo lag.

The 455 lb.-ft. (617 Nm) of torque can be hard to manage in city driving, as the ML has a tendency to surge despite carefully controlled throttle inputs.

At the end of my journey, one thought occurred to me as I was rolling into the Grand Traverse Resort, site of MBS: The smallest vehicle Mercedes makes, the 1,800-lb. (816-kg) Smart Fortwo, gets a relatively paltry 34 mpg (6.9 L/100 km).

But the ML, which is as aerodynamic as a brick and weighs more than twice as much, can return 35 mpg under the right circumstances.

Between the two, the big CUV is the hands-down winner.