In 1936, Mercedes-Benz built the 260 D. It was considered to be the first real production diesel passenger vehicle the world had seen. Since then, Mercedes-Benz has maintained its diesel technology setting top speed records, distance records, and even drove a fleet of them from Paris to Peking. It was no wonder we jumped at the invitation to sample the latest BlueTEC offerings in the hills of Vermont.
The company brought out three different platforms for us to sample: The ML320, GL320, and R320. We had already driven the E-Class BluTEC earlier this year and walked away stunned by the giant torque, especially matched with its fuel economy and quiet, smoke-free operation. We didn't expect the heavier platforms to offer the same level of performance as the lighter E-Class, but we went in with extremely high expectations anyway.
Many of the offerings from competing companies feel very much like diesels. The engines rev slow, the low-end torque is readily apparent, as is the low redline. Even without looking at the tachometer in most of the other cars, you can tell from transmitted engine vibration frequency that you just aren't revving that high, and really there is no desire to. Mercedes-Benz on the other hand manages to make its diesel products feel more like gasoline engines. It may be a matter of isolation, or even ratio selection, but the mechanical feel of the driveline doesn't feel like a typical diesel. With that said, it does feel like the car is continually short shifting, and the engine feels as though it could spin a little higher. It doesn't keep all its power down low and fall off completely at the high-end. The engine redlines at 4500 rpm and its horsepower peak is all the way up at 3800 rpm.
It won't feel like a gasoline engine in the fuel economy. The ML and R are both rated at 24 mpg on the highway, while the bigger, heavier GL falls just shy of that at 23 mpg. In the twisting, climbing, and falling roads of Virginia, our test vehicles were actually returning closer to 27 mpg in the GL and 29 mpg in the ML and R. These were rural highways with average speeds hovering between 50-65 mph, so no doubt economy would drop slightly at speeds 10-15mph higher.
The real surprise in the group was the R-Class. The big people mover never received a warm reception by the SUV-crazed U.S. population. It sits slightly higher than a sedan, but doesn't feel as top heavy as your average SUV. It comfortably, if not luxuriously, seats six adults, or four adults with three children sardined into the second-row bench. During the weekend we had the chance to try all three rows, and I must say that all were equally comfortable. The R-Class feels more like a limousine than a typical family hauler. The driving experience is not meant for enthusiasts, but the odds of finding five passengers who don't get motion sick are slim to none anyway.
The ML is still the least desirable vehicle in the Mercedes-Benz lineup. The diesel does improve economy, but that appears to be the only advantage over the ML550 we recently tested. If Mercedes is trying to illustrate the seamless transition a customer can make from gasoline to diesel, then it has succeeded completely. If they try to make it sound more exciting to drive diesel, than the ML is not the platform to do it in.
The GL was decent, but the fact that Mercedes-Benz decided to show, but not offer drives in, a diesel hybrid GL left us wanting more. Without driving it, we can only speculate that it may be the ideal driveline for a 5,400-pound SUV. The standard GL320 feels sluggish off the line, yet at highway speeds has impressive passing ability. In Mercedes-Benz tradition, all three vehicles are deceptive in their acceleration. Drivers will flash by slow-moving RVs on two-lane roads without even feeling like they've gained speed.
As with most next-generation clean diesels, Mercedes-Benz is relying on both urea (AdBlue) injection and particulate filters to meet both U.S. and European emission standards. BlueTEC does require low-sulfur diesel, which is currently available nationwide.
One of the challenges facing all diesel engine producers will be the rising cost of fuel. Most consumers will look at the 15-20 percent higher cost and be put off. Most will not consider the fact that in the case of the ML320 compared to the ML550, the former gets almost 50 percent better fuel economy. It looks like it's time for some creative marketing person to teach Americans how to do math.
Mercedes-Benz 3.0-Liter Bluetec
*ArchitectureTurbocharged, 72-degree, dohc, four-valve per cylinder V6
210 hp @ 3800 rpm
398 lb-ft @ 1600-2400 rpm