2011 X5 35i "greener" than 35d?
 

There is some interesting information at Fuel Economy for the 2011 X5 models. Using the "Compare Side-by-Side" link Side-by-Side Comparison you can add up to 4 models, so I added the 35d, 35i, 50i, and M to see what the results were. I tried to post a link to the page, but that doesn't work, nor does pasting the content into the editor.

What really caught my eye is the "Energy Impact Score" which measures the "Annual Petroleum Consumption" in barrels. Based on a 15000 mile per year average at 55% city driving, the 35i uses 17.1 barrels, the 35d 17.9 barrels, the 50i 21.4 barrels, and the M 24.5 barrels. It was surprising to see that the 35d consumes more barrels of oil than the 35i. I couldn't find any information on the site about this, but I've heard/read that more gasoline can be extracted from a barrel of oil than diesel, so perhaps that is the reason.

The "Carbon Footprint" measures "Annual Tons of C02 Emitted" and the values are 9.3 for the 35i, 9.6 for the 35d, 11.6 for the 50i, and 13.3 for the M. This must also have some factor for diesel versus gasoline because the 35d would use less total gallons of fuel per year.

I'm not a greenie, despite living in the Boulder, Colorado area where lots of such folks congregate, but it does surprise me that the diesel comes off as being less "green" than the gasoline version. It seems likely that in the "real world" the 35d will be even more efficient compared to the 35i than the EPA ratings suggest, but perhaps I'll be proven wrong by the 8 speed transmission and the "Efficient Dynamics" features.

Any early 35i owners getting any indication of MPG? The 35d owners seem to report 22-24 MPG in mixed driving, with up to 30 MPG for highway trips. In my '07 335i I've been getting 22-23 on nearly every fillup, 25 MPG or so if there are some longer trips involved. It's hard to imagine that 35i could do as well as my 1500+ lbs. less car, but again, maybe those BMW engineers have worked some magic.

Holy crap I want an Eco Credit on my 35i.

I had a '10 35d and now have the '11 35i

My 35d was right around 24mpg in mixed driving. So far the 35i is around 21.5mpg in the same driving, but it's early, I only have 1500 miles on the 35i. My 35d picked up around 1mpg after breaking it in, so I'm curious where the 35i lands.

On a trip with mostly freeway the 35i maxed out a 22.6mpg while the 35d hit 25mpg on average.

Considering how the 35i drives, I am very happy with the mileage so far. I am keeping a detailed log for the 35i to post at a later time.

Bigx5er
 

How's the 35i drive compared to 35d? How's the acceleration feel compared?

That's pretty good MPG - anxious to see your log later.

The official BMW statistics for the xDrive35i versus the older xDrive35d and the new xDrive40d (not available in the NA market)

xDrive35i
Combined consumption: 10,1 l/100km
CO² emissions: 236 g/km

xDrive35d
Combined consumption: 8,3 l/100km
CO² emissions: 220 g/km

xDrive40d
Combined consumption: 7,5 l/100km
CO² emissions: 198 g/km

So between those three motors, both diesels are cleaner and consume less fuel.

Credit for this post, from the 'other board', goes to AzNM32.

Be careful on how you interpret all these statements. In general, diesel contains longer length carbon chains (more carbon bonds) than does gasoline, therefore it has a greater energy density than gasoline. Hence a gallon of diesel has more energy than a gallon of gasoline. Hence a naive "energy efficiency" when comparing diesel to gasoline at the gallon level. But if you compare the energy content on a carbon bond basis they are almost equivalent. Both are extracted from a barrel of crude. And in general, there are more medium-length carbon chains (gasoline) in crude than the long-length carbon chains (diesel). When you compare gasoline versus diesel at the crude level, the advantage of diesel over gasoline almost disappears. Therefore both statements regarding the different motors consumption values (OP's and XXX555's) could be correct. To be fair to society and ecology, we should, more often, compare an engine's energy consumption at the crude level and not the gallon level.

I strongly prefer the 35i over the 35d. Response from the 35i is immediate (part of that may be the new tranny). At low speeds, the 35d always felt a little laggy where the 35i does not. The 35i also feels lighter/more responsive overall. I'll withhold my final thoughts until the 35i is totally broken in. I drover the 35d for 11K and only have 1500 miles on the 35i.

I do not tow anything, so the extra torque from the 35d isn't as important to me.

That said, I recommend driving one of each.

bwoodahl has some good comments on diesel efficiency at the crude oil level. Given those comments, and the US government website calculations, it would appear that in terms of reducing the number of barrels of imported oil, adopting diesel engines will hinder progress, not help. Interesting. I don't have experience calculating the barrel impact, but I have done a lot of certified fuel consumption tests on diesels, in industrial applications, and we always took the calorific value of the fuel (by weight) into account, we never worked in litres and gallons.

XXX555, you provide official BMW figures for CO2, but they include models not available or certified in the US. That suggests to me that those figures are not determined using the US or Canadian emission test cycles, and that the engines tested are not in fact certified for the US. Outside North America, engines are tuned to meet local emissions regulations. That makes those figures irrelevant in North America, unless the 35i and 35d figures are NA test cycle figures, and only the 40d is calculated differently. It is not correct to say that diesels are cleaner, only that these figures show lower CO2 emissions. There is a lot more to it than CO2, and to focus only on that figure is cherry-picking.

SkipSauls, you have touched on a significant issue with diesels vs gasoline engines in terms of environmental impact. There are many ways of calculating environmental impact (really, we should consider manufacturing and disposal impacts, ie full life cycle impacts). Addressing just the carbon footprint issue, it is not correct that the site you link measures carbon footprint based on CO2 emissions, although the short caption does say that. The Info button says the following:

The carbon footprint measures greenhouse gas emissions expressed in CO2 equivalents. The estimates presented here are "full fuel-cycle estimates" and include the three major greenhouse gases emitted by motor vehicles: carbon dioxide, nitrous oxide, and methane. Full fuel-cycle estimates consider all steps in the use of a fuel, from production and refining to distribution and final use. Vehicle manufacture is excluded. (U.S. Department of Energy, GREET Model 1.8, Argonne National Laboratory)

That gets to a real issue, which is that while diesels can do well on CO2 emissions (which is what the EU focuses primarily on) they don't traditionally do as well on NOx emissions (which are responsible for smog, and which is what the US and Canada focus primarily on). Urea injection is designed to lower NOx (which is why North American vehicles have urea injection systems such as Blu Tech, and EU passenger vehicles don't have it yet). The Carbon Footprint score considers the NOx emissions, expressed as CO2 equivalents, as well as calculating them over the full fuel cycle (including refining).

It isn't surprising to me that diesels are not as green by some measures. By many consumer measures, they are wonderful, but the above illustrates a more complete picture when considering their impact.

Now, to extend the discussion, look at the X6 Hybrid on the same site. It is worse than either the 35i or 35d in carbon footprint, even without considering the life cycle impacts like battery production and disposal. Wonder who is going to tell the hybrid fans?

Good discussion, thanks for posting.

JCL, your comments are appreciated.

I will comment only on your analysis of my post.

You entirely misunderstand the intent of my post. I don't care what the actual numbers are or where they were tested. As long as they were tested the same way and showing the 35d with lower fuel usage and CO2, I was responding to the OP. You may consider the info on the 40d a bonus.

A lot of variables but twisting the numbers to justify a 35i purchase over a 35d purchase in the name of better fuel economy is so wrong.

Additionally, I understand that diesel fuel is the waste product of gasoline, lubricant and plastic creation from a barrel of oil. Another bonus.

I'd also like to see a 8spd 35d v. 35i as the 8 speed adds over 6% mpg improvement per a BMW quote I previously posted. The bonus info on the 40d may be closer to 35i apples to apples, with the 35d in its 3rd year and the 40d for the US inevitable.