Experiencing The New Diesel-Powered BMWs.

While you may have already read a thing or two about BMW’s new compression ignition offerings, you may not have heard all the details, and you may have some questions. I sure did, and I did my best to answer them here. Get coffee, go read, see huge gallery.

Cars:
2009 BMW X5 xDrive35d, from here on to be known as BMW X5d. The vehicle was surprisingly stripped, even without the common premium package. It had about 500 miles on the odometer.

Visually, the biggest differences between the diesels and their gasoline counterparts are badges. On the 335d the intercooler and twin exhaust pipes will have you thinking 335i, while the front mounted intercooler is a new thing on the X5d. Biggest difference inside is the 5000rpm redline in both cars.

Engine:
Like on most new cars today, open the hood and you’ll see nothing. The engine is a three-liter, aluminum (yes, aluminum), DOHC, 24-valve, common-rail direct-injected, in-line six with a 16.5:1 compression ratio. The engine features variable intake manifold and double-VANOS valve control. All of that is supplemented by a pair sequential, differently sized turbos. Big air-to-air intercooler is located within the front bumper cover of both cars. The engine produces 265hp at 4200rpm, but more importantly 425lb-ft at a low 1750rpm. Unlike a traditional diesel there are no glow plugs, as the direct injection system has the ability to start a dead cold engine all by itself.

What the engine does have, as does just about every other new diesel, is urea injection. Here is how urea injection works: most of the diesel soot gets trapped in the particulate filter located just behind the exhaust manifold, where it eventually burns up. The stuff that gets through and/or the burned remnants (NO/NO₂), get trapped in a secondary catalytic converter known as the SCR catalyst (selective catalytic reaction). When the urea is injected into the SCR, a chemical reaction occurs which generates ammonia (NH₃). The ammonia in turn reacts with NO/NO₂, converting it into nitrogen (N₂) and water vapor (H₂O). Got it? Chemistry lesson is over, class dismissed.

Because urea freezes at 12 degrees Fahrenheit, the cars are equipped with two urea tanks: a small active tank which is heated, and a larger passive tank which is designed to expand once the urea freezes. In the X5d the passive tank is located under the hood and the active tank is located near the transmission. In the 335d, both tanks are located where once a full-size spare tire¹ lived (RIP). The tanks hold enough urea to last between scheduled oil changes.

When you’re running low on urea, you’ll get a message on the dash and an estimated remaining travel distance. Each time you start, you’ll be getting dash warning, and if you keep ignoring them, eventually the car will warn you that it is the last time is starts. If you shut it off, you better be at a dealership or calling the toll-free number written on your “tool kit“². This setup was mandated by the EPA and without it, the diesels would not be allowed for sale in the U.S. Worry not, as soon you’ll be able to buy urea at any gas station. All urea designed for diesels is the same, so the one from your Mercedes dealer will work too.

Living in New England begs obvious questions – what happens in the winter? How long will my battery last with that heated tank? Does it stay heated the whole time? No, the active tank is automatically heated once the doors are unlocked or opened, and by the time you sit down and make yourself comfortable, the engine is ready to start, in all temperatures. While diesels of the past had huge batteries to ignite the glow plugs, the batteries on the diesels are the same size as on their gasoline drinking brothers.

Transmissions, etc:
Both, the X5d and 335d, are only available with a six-speed automatic transmission. The gear ratios are the same for both cars, but differential gearing is taller on the X5d. BMW says that they do not have a manual transmission that can manage the torque of the diesel engine. The 335d comes in rear-wheel-drive flavor only, and the X5 comes only with the xDrive all-wheel-drive system. Like all non-M cars, neither vehicle is available with a limited slip differential. There is no low-range on the X5, and I wouldn’t venture far off-pavement in it.

Sights and Sounds:
The diesels are not distinguishable at first sight, only once you hear them start up and see the badges do you say to yourself “oh, it’s the diesel”. Once at idle, the engines are so quiet that standing more than twenty feet back you wouldn’t know which X5 you’re looking at. When driving, only under full power will you notice the real change in sound; the diesel engine is louder and moves slower than the gasoline engine. What you will not notice is the rate of your acceleration, this thing boogies!!

Driving:
Punch the 335d off the line and you will see a flashing traction control light on your dash, because the tires will break loose under anything more than average acceleration. It is not a kick-in-the-butt type of violent acceleration however, you won’t get thrown back into the seat but rather you get steadily pressed into it, much like a passenger jet taking off. Unless you have lived with diesels or V12s this will take a little getting used to but your smile will grow wider each time. Highway acceleration in both cars feels smooth and almost uneventful, it will make you wonder if the speedometer is properly calibrated.

The 335d tester looks like it’s wearing a well tailored dark suit, and with the smaller non-sport wheels, it is giving off an impression of mild-mannered conservatism. That suit, however, is worn by a bad wolf. Some will believe that you have actually purchased this car for its excellent gas mileage and legendary diesel durability but what you really got with the 335d is complete sleeper. The original E28 M5 was called a wolf in sheep’s clothing, but today’s E60 M5, with its huge quad exhaust pipes, vents, and various bulges makes no secret of what it is. This may upset some a few souls, but the wolf is dead! Long live the new wolf, now in a slick dark suit. Yes, the 335d that good, and there is nothing on the market quite like it.

The X5d was not as transparent in its personality (or two) as the 335d. Most of it can be attributed to the extra 1400 pounds that the engine has to pull around. Immediately off the line the X5d didn’t have the pull of the 335d, but once up to cruising speed it pulled like freight train. Highway acceleration and engine flexibility being its strong points, it made overtaking uneventful and easy. Driving the X5d around, I couldn’t help but feel like I was missing something. It was similar to being given a trivial assignment and an abundance of resources to complete it. The X5d felt as though it was not being challenged, if it could talk it would say “c’mon, attach that trailer, slap on the E30 and let’s head for Lime Rock!” While the tow rating of all X5‘s is the same, at 6000 pounds, there is no doubt in my mind that the diesel version would make such task downright enjoyable.

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I’d like to thank everyone who has made this article possible, you know who you are. Thank you. A version of this article will be published in the July issue of Boston Bimmer, a magazine of Boston Chapter of BMW-CCA.

¹ Neither car appeared to have a spare tire, a jack, or a wheel wrench.
² Tool kit consisted of a tow hook, screw driver, and an 800 number.