My dad an I test drove a Mercedes-Benz E350 Bluetec this past week and despite my high expectations, we were both pretty disappointed. My dad ruled out a further test drive, however I would be willing for another, longer drive if possible.
I don't think my dad used the glow plugs on startup, being unfamiliar with Mercedes' "auto start" (non push button, i.e. turn the key and release, it cranks for you.) The car needed about 2-3 seconds of cranking before firing, and once it fired it sounded good, with a bit of clatter (35*F ambient). The car itself was everything I expect of Mercedes-Benz, excellent build quality, very comfortable seats, great ergonomics and a very solid structure (I entertained myself while the dealer was fetching test drive plates by closing the door a few times - can you say bank vault?
) Anyway, once pulling out of the spot, I noticed a few vibrations at low revs (1,300 RPM) and that the transmission (7AT, torque converter) seemed to bobble the engine rpm much like our DSG can do (the tach bobbles up and down on upshift). Once driving on the road and warmed up, to my ear, the car made nice diesel noises, however sounding much coarser than the BMW 335d we drove this time last year in similar temperature. However the E350's V6 was much, much quieter, and certainly lacked that perfect (IMO) straight six balance and sound.
My biggest complaint about the E350 was the seemingly poor execution of the pairing of the V6 turbodiesel and the newly redesigned 7AT gearbox for 2012. The gearbox always seemed to be hunting for a gear to stay in. It wasn't jerky, just somewhat lazy and unintuitive, the 335d's 6AT behaved much better, from a performance and comfort standpoint. It also was reluctant to kickdown, taking at least a second before any surge of torque piled on. I wasn't driving, so I could not evaluate if this was solely the gearbox, or indeed a hint of turbo lag. Most likely the gearbox. Chassis impressions were decent, and the ride was velvety and very quiet. My dad said steering was a bit light, but ok in other regards. We did a few 80-20 stops and from the passenger seat the binders (four piston calipers front with cross drilled internally vented rotors, single piston solid internally vented rears) provided more than enough stopping power for a two ton sedan. My dad said that the pedal was a bit spongy during those stops, however. The 400 lb/ft of torque did not seem all that impressive compared to the 335d, (yes the 335d is a few hundred pounds lighter, and more power/torque) - it will be interesting to drive the Bluetec with the new updated V6 in the ML and S-Class diesels, which has 240 hp (from 210) and 450lb/ft.
When we got back to the dealer, he offered a test drive in the gasser E350, and my dad (and I, I have to admit) were much more impressed. The powertrain "glitches" from the diesel were gone, and it felt like a proper E-Class. That being said, if I traveled almost all highway miles, the E350 Bluetec would be high on my list of luxury midsized sedans.
Sorry for the rant, just felt like sharing my opinion on a German oil burner.
Oh, and one more thing - bring on the 535d