Am I analyzing this right? Diesel vs Petrol

[kck7]

Originally Posted by pfbz

Plenty of diesel X5 apologists. That's fine, go your own way and be happy. For me, until they introduce the 40d with the eight speed, the diesel is the third choice engine in the 2011/2012 BMWUSA X5 lineup.

The smell I was referring to is the smell of diesel fuel itself... Yes, I have a diesel. F350. Just touching the diesel pump leaves a stink on your hands if you don't wear gloves.

As for "real world performance", you are totally believing your own BS if you think the 35d will outperform the 35i in any measurable performance category.

I know diesel defenders think that EPA is "unfair" in their testing... real world vs. actual, etc., but certainly it is more meaningful and accurate then individuals saying things like "I get 22 mpg every fill up..."

There are various reasons people like the diesel. As for me, I drove both the 35i and the d. The i posts slightly better numbers but owing to its torque the d feels faster. As I bought the car for, among other things, enjoyment and not tracking or drag racing, this works for me. We all probably know the phenomenon where a not-so-fast car feels faster, or at least more fun than its speedier competition, and becomes a hit as a result (see Mazda Miata).

[F150 Duke]

I think pfbz is forgetting they are geared towards different owners too. For example, I need to tow a 5,000lb boat and trailer once a week during the summer. The 300hp/torque of the 35i is good but won’t get my boat up to speed on the highway (65 mph) as fast at the 425 torque in the diesel. Not only that, at highway speed up a slight grade the 35i will be downshifting far more than the 35d when towing the 5,000lb boat.

That being said, if I didn’t need to tow, I’d hands down pick the 35i. The lack of a metallic noise on heavy acceleration in the 35i would be my reason why. MPG is a little better in the d over the i but not enough to justify the extra .40 per gallon of diesel in my area. Could the 35i tow my boat? Sure, but I just feel it’d be too much strain and annoying to constantly hear it downshift.

If cost was now option on the purchase price and I didn’t mind the same mileage I currently get in my truck, well then I’d buy the V8. But for ME, that’s not the case. True to the saying in more ways than one “Your mileage may vary”.

[pfbz]

Originally Posted by JCL

Fully agree that the EPA figures (which have a large number of correction factors applied to the as-tested figures from the dynos) aren't particularly related to the real world.

However, I don't see why the diesels would be closer to the EPA figures than the gasoline models.

EPA figures were not designed to promise a purchaser what they would get, but were rather designed for comparison between models, repeatable tests. That is what people are doing here with the 35i and 35d.

Real world test results by lots of posters here puts the spread between the 35i and 35d at around 3 mpg, which is interestingly the same spread the EPA reports.

Exactly. The claim that somehow it is easier to hit the EPA numbers in a diesel than a gas is purely anecdotal, especially for highway mileage. I am sure, however, that those obsessive about observing and reporting their diesel mileage drive in a way to help achieve maximum MPG's...

[pfbz]

Originally Posted by F150 Duke

I think pfbz is forgetting they are geared towards different owners too. For example, I need to tow a 5,000lb boat...

Actually, I agree... Heavy towing is one area where the diesel probably moves ahead of the 35i. If I towed anything larger than my light aluminum moto trailer with a few dirt bikes on it and didn't already have a heavy tow vehicle (F350), I might consider the 35d over the 35i.

But the original poster started a thread about Diesel vs Petrol MPG, used some funky mpg data from unknown source as well as choosing to compare the 35d to a twin turbo V8 instead of the 35i, and then asked:

"What am I missing to draw an accurate conclusion?"

My original post was to illustrate that he was, IMHO, missing quite a bit. Good data on MPG, a more realistic 35i vs. 35d comparison, and the relatively small actual impact on annual fuel costs.

So, how many 35d owners tow something over 3,500 pounds more than a few times a year? Or even have installed a hitch on their 35d's??

[JCL]

Originally Posted by pfbz

But the original poster started a thread about Diesel vs Petrol MPG, used some funky mpg data from unknown source as well as choosing to compare the 35d to a twin turbo V8 instead of the 35i, and then asked:

"What am I missing to draw an accurate conclusion?"

I believe the OP owned both vehicles at different times, and used his own actual mileage figures. The original question was just about the calculation formula to be able to determine if his new vehicle was cheaper to run than his old vehicle.

[midwest x6]

Originally Posted by JCL

I believe the OP owned both vehicles at different times, and used his own actual mileage figures. The original question was just about the calculation formula to be able to determine if his new vehicle was cheaper to run than his old vehicle.

Ding, ding, ding!!

Hey, they're all great power-trains in their own right. Any of us are damn lucky to own or lease any of em.

[Penguin]

I prefer the diesel because of the low RPM torque. Driving through the mountains on vacation, it climbs most steep upgrades with nary a downshift... it just pulls and pulls as if it was a gentle slope.

Now, I also have a Z4, and I would not want a diesel in my Z4. But for the X5, the diesel's Torque/RPM curve is superior to a gasoline engine, in my opinion.

A 500 miles plus range is also quite nice when traveling on vacation, e.g. I averaged 26-29 mpg on the highway, cruising most of the time at 65-75 mph.

[JasonG]

I dont tow, also have a diesel truck for that use...to me, for everyday use/commuting/drivability on the street the diesel's torque is fabulous and infinitly usable...and the mileage is nice upside...i had a choice between an 35i and a 35d...I chose the d....would do the same thing all over again....if paper numbers / performance was what i was interested in i'd get the 50i or M or a < 5k lb car. I dont think mileage is significant enough to use as a decision point between a 35i or 35d....i'd go off of ultimate price and what best suites your needs / driving habits / style. agree with the above, lucky to have one and truthfully i'd be happy with a base x5, the fancy stuff is nice, but the driving experience is what puts a smile on my face, they're pretty nice rides!

[Lawfarm]

I agree and disagree with posters above.

I agree that many of the benefits of the diesel are intangible. The torque is great, the driving is great. Driving feel is obviously subjective. In my opinion, the diesel drives better than the 6 cylinder gasoline engine; the diesel, to my calibrated butt, doesn't feel like it has to work as hard as the gasoline engine to accelerate or drive. In 99% of my real world driving, I suspect that the diesel performs better than the gasoline engine would. It is rare that I need 100% of engine output...and to my taste, the diesel does a better job of moving my several tons of X5 around seem effortless.

I also agree that on a car costing as much as an X5, affording the gas shouldn't be a concern.

That said, I do greatly value the diesel's fuel economy. I have some years where I drive 30k miles or more. I can account for the car's purchase price (and to get a car that I'm happy driving, I have to spend some money). But if there are two cars, and one can do the job for substantially less $$ in operating costs (maintenance, fuel, etc.), then all else being equal, I'll take the lower cost option. I also personally feel that there is a substantial environmental benefit to better fuel economy. Sure, if I wanted the best possible results, I'd be driving a Prius or something...so it isn't the decisive factor for me, but it is a factor. And with fuel prices being as volatile as they are, given a choice between better mileage and worse mileage, I'll take better mileage every day of the week and twice on Sunday.

I guess I don't perceive any detriment to the diesel (versus the gas) from a subjective perspective...I see benefit. And from an objective perspective, the slight performance difference (which rarely, if ever, comes up in real world driving) is outweighed by the mileage difference--again in my opinion.

Regarding real world mileage, perhaps my experience is atypical. I've now put just over 4,000 miles on my X5 that I've been tracking mileage for (after an initial acclimation period that I'm excluding). All of that has been winter driving, on a new set of snow tires, with cold weather, winter fuel, etc. My driving during that time has been about 30% tollway (average speed between 60-70mph, depending on traffic; 4-8 lane tollways); 5% urban (stop and go), 30% rural (average speed 60ish; 2 lane roads), and the balance suburban (30-50mph). In that time, the car calculates my average economy at 27.3mpg. I calculate my fuel economy, hand cal'cd based on actual fuel usage and miles travelled, at 27.44mpg. No smoke and mirrors. No 'egg on the gas pedal' driving. I think that's substantially better than what I'd have in a gasoline model...and I think a substantial part of it is the driving that I do (a lot of 'solid-state' cruising, without acceleration/deceleration). I also suspect, based on past vehicles, that the mileage will go up this summer. So figuring fuel usage at 22mpg combined doesn't make a lot of sense for me.

I'm sure the mileage police will come in and arrest me for indicating that my average mileage thus far is 27.44mpg. But here are the figures, from when I started keeping track (about 5-600 miles after I got the car, and zeroing out previous fuel):
4131 miles
150.5 total gallons burned
27.448505 mpg.

I usually buy diesel at a local truckstop, and the price has been hovering around $3.47 lately. Let's call that $3.50.

$3.50 x 150.5 gallons = $526.75 in fuel costs, for 4131 miles. That's about $.127 per mile in fuel costs.

Let's compare to a gasoline engine. We can be generous and say that you'll get 20mpg average.
4131 miles
20 mpg
206.55 gallons (37% more fuel).

We'll be generous on the fuel costs, too, and estimate $3.35/gallon (a little cheaper than current gas prices, and significantly cheaper than premium fuel). That's $3.35 x 206.55 = $691.94 in fuel costs, for 4131 miles. That's about $.167 per mile in fuel costs (about $.04 per mile more, or about a 31% increase in cost per mile). Every 100 miles you drive, the cost difference is about $4. Every 1,000 miles, the difference is $40. Every 10,000 miles, the difference is $400. Is that a huge difference? No...probably not enough to make a difference in my purchase decision. But I'll still take the extra $400. If you carry that out to a year where I drive 30k miles, I'm saving $1,200/year on fuel...which is basically like having one month without a car payment--if you're figuring total cost of ownership. (Of note, the difference becomes more substantial if you use the EPA figures of $2.63 for diesel and $2.82 for premium).

[JCL]

My thoughts on the diesel are that it is a marginal improvement over the gasoline engines in efficiency, which is OK in itself, but that it doesn't move us ahead as much as it could have. It is like BMW squandered a great opportunity in the North American market, in my opinion.

I will leave aside all the driving dynamics of diesel vs gasoline. It is a personal thing, some people like the effortless torque, others like the feel of a BMW gasoline engine. I really like diesels in trucks, I just don't think of my BMWs as trucks, so in my case the current diesel offerings from BMW don't fit my requirements. Also, the diesel is often compared to the 30i (no contest) when it needs to be compared to the 35i. The torque that people are so happy with is more a product of the turbochargers than it is the diesel fuel system.

What I think BMW really blew with their diesel introduction here is the chance to make a statement on improved energy efficiency. That is even more true with the 335d introduction, which could have been a 320d introduction just as easily. BMW essentially said "here is a new diesel, it performs almost as well as our fastest model, and the fuel mileage isn't bad" when they could have said "here is a new diesel that shows you what we can do" If they had done that the 3 series diesel introduction may not have bombed as it did. With the E70, all of the diesel hype comes down to about 3 mpg compared to current technology gasoline engines, in mixed city/highway driving, in an X5. It doesn't change purchasing behaviour. As many have pointed out, it just isn't enough to get excited about. I think the E70 diesel is a impressive car, but they put that engine in a vehicle that weighs 5200 lbs. They used the crutch of the diesel to get lazy and let the car get larger and heavier. Good enough is the enemy of great. What they could have done is make the car lighter and more efficient, and put an efficient (smaller) diesel in it, and really made a statement. A new X3 with a four cylinder diesel (eg 20D) is 1000 lbs less, the same size as the original E53, and definitely a step in the right direction. I wonder what changed that got BMW product planners to alter course. I am glad they did so, but I don't know what they saw differently.

There is a place for large vehicles. I use them myself when I have to move six or seven people. I just see so many E70 and similar vehicles on the road with a single person in them. One (positive) way of looking at it is that some of them are getting 3 mpg better than the gasoline models, and using less of the world's energy (which is a good thing) but I imagine what could have been. They could be getting 10 mpg better, in a lighter vehicle. It could have the same driving dynamics. But instead we seem to be planning to extend the life of large heavy single passenger vehicles by saying "it is OK, they are diesel". My last diesel was a Passat. It had the largest diesel, the Audi A6 version of the 1.9 four cylinder. I got 50 mpg (Imperial) with it, with a family of four, and a month of luggage, cruising at excessive speed in Europe. That was 10 years ago.

OK, enough philisophical ranting. I hope all the E70 owners enjoy their vehicles, especially the 35d owners. I also hope that BMW offers alternative choices that take advantage of the engineering they are capable of.