BMW Deisel

Originally Posted by wxmanCCM

My experience is just the opposite.

The only issue I've had with my 2003 Dodge/Cummins in almost 125,000 miles is the lift (low-pressure fuel) pump failing. I replaced it with a FASS system which cost about $500, IIRC, but the stock replacement was much less than that.

I also had a 2002 Jetta TDI for about 128,000 miles before the 335d, and the only issue I had with that was one of the window brackets breaking, allowing the window to fall into the door. It was fixed under warranty. It was sold to an acquaintance of my son, and last we knew, it was still going strong with over 200,000 miles on it.

All of the gasoline vehicles I've owned have been far more problematic, although to be fair, we haven't had a gas car since 2002.

There is a reason I am saying 200-300k. Most vehicles I have owned, gas or diesel have not had much of any issues prior to usually 125-150k miles. Matter of fact I am a firm believer than any modern car should last upwards of 150k miles before an expensive repair is needed. My truck I think had just a sensor go bad prior to 125k and I think my brothers truck had a coil pack and some ball joints go bad, I guess then I should say the diesel truck is more reliable than the gas one. Put more age on my truck and compare it to my brothers 5.4L and when some common problems happen the diesel ends up being a lot more to fix. For example both trucks due to fuel pickup design issues have lost their fuel pumps. When the gas truck lost its pump it was just a matter of a tow and pump replacement, when the diesel truck lost its pump it killed one injector which in turn killed the other injectors on that bank and I got lucky did not kill injectors on the other bank. The diesel truck repeatedly has been more "sensitive" to one failure causing other failures. I had similar experiences in the past with the few 1985 Mercedes and Chevies I have owned.

I know people who have/had Cummins and TDIs and had amazing luck in regards to the powertrains lasting just like I know people with the 7.3L Fords and had amazing luck. Seems to me though the issue here is as engines(gas or diesel) and emissions change with advancing years it becomes a gamble as to whether the new ones will be stone cold reliable or not. Sometimes when needing to buy a new vehicle we do not have the luxory of picking something with a powertrain that has been around long enough to prove itself.

The newest gas vehicle that I owned and actually drove was the 2000 Accord we replaced with the 335d, put around 284k miles on that before it finally made no sense to keep fixing. I do own a 2008 F150 but provide that to a family member so don't actually see it much, it has had zero issues for the 100k or so miles on it but not sure that proves anything. I do have a couple of Mustangs but they are older and about as reliable as one can expect for their year models.

Originally Posted by Snipe656

...For example both trucks due to fuel pickup design issues have lost their fuel pumps. When the gas truck lost its pump it was just a matter of a tow and pump replacement, when the diesel truck lost its pump it killed one injector which in turn killed the other injectors on that bank and I got lucky did not kill injectors on the other bank. The diesel truck repeatedly has been more "sensitive" to one failure causing other failures. I had similar experiences in the past with the few 1985 Mercedes and Chevies I have owned. ...

The 2003 Cummins was the first year with a common rail fuel injection system, and the lift pump failing caused no other damage. As a matter of fact, the truck still ran, albeit with little power. It's my understanding that lift pump failures on earlier models caused extensive downstream (injector) damage as a result.

I agree that emission control probably has resulted in more of a gamble with respect to reliability.

Originally Posted by wxmanCCM

The 2003 Cummins was the first year with a common rail fuel injection system, and the lift pump failing caused no other damage. As a matter of fact, the truck still ran, albeit with little power. It's my understanding that lift pump failures on earlier models caused extensive downstream (injector) damage as a result.

I agree that emission control probably has resulted in more of a gamble with respect to reliability.

Interesting enough, mine still ran too and with next to no power.

Yeah, the emissions control actually is what bothers me a lot with the newest diesels. If I were to keep my 335d for the long run I am pretty certain I'd end up getting some of the controls bypassed since looks like this is becoming a possible option via certain shops.

I actually don't mind that diesels have cost me more to keep on the road else I'd not buy them. I am just pointing out my personal experience has been they are not cheaper to maintain/repair. I don't care enough to factor in fuel costs to see how that offsets overall ownership costs since I buy vehicles because I like how they drive not because of what their mpg is. Factoring in fuel costs though might easily offset things since clearly less money is spent for diesel than gas over the lifetime of owning things.

The new gasoline engines are no less complex or problem prone than diesels. Direct injection, turbo's, and pollution controls, not to say much about all of the electronic controls of stop/start let alone hybrid powertrains that are coming along.

Discussing anecdotal evidence or "stories" of past experience, especially before model year 2000 or so, is just a waste of time. We really don't know how reliable any of the new designs will be, gas or diesel, after 200,000 to 300,000 miles. The reality is, engineering cars has ALWAYS been a compromise of cost and longevity. You don't want to design a fuel pump, for example, that will run a million miles but that costs as much as a whole engine to manufacture.

Each manufacturer makes engineering decisions, as well as its suppliers, and hopefully new technology comes up with longevity as part of the improvements that are made.

Many in the luxury car segment have extended warranties and this along with the impression of how durable or fast these cars are/can be brings people to put more stress on the cars - no BMW or Mercedes is a Porsche race car no matter how well its made! I've followed the reliability stats on all these cars and believe they are mostly abused in the US and not properly treated as they are in Europe. Porsches, on the other hand, are treated much better in the US as they are considered to be race cars in Europe.

Just my observations. My $.02

PL

My stated example was using a 2003 and 2005 year model trucks, far from ancient vehicles and it was showing the "sensitivity" levels of the different types of engines. The fuel pumps failed because of an engineering design flaw with the fuel tank pickups. This was the difference of an $800 repair on the gas truck and almost $2.8k on the diesel, same root part failed on both but the diesel as usual had more stuff downstream fail because of that. That has been a consistent experience for me on every single diesel I have owned. Take it for what it is worth.

Originally Posted by henrycyao

Diesel fuel has about 15% higher energy content per gallon than gasoline. So it gets 15% MPG better given the same level of technology. To get above 15% MPG improvement has more to do with the tuning characteristics of the engine and how you operate.

While the BTU density of diesel fuel vs. gasoline is a major part of the differences in mileage, the diesel engine cycle has inherent thermodynamic efficiency advantages over the gasoline Otto cycle in the real world, primarily expressed in the higher compression ratio of the Diesel cycle, i.e., it's not just the energy content of the fuel that makes the difference.

Originally Posted by Penguin

While the BTU density of diesel fuel vs. gasoline is a major part of the differences in mileage, the diesel engine cycle has inherent thermodynamic efficiency advantages over the gasoline Otto cycle in the real world, primarily expressed in the higher compression ratio of the Diesel cycle, i.e., it's not just the energy content of the fuel that makes the difference.

Gasoline engine's compression ratio is now on par with diesel.

Here is a google search of some of the engine discussion. This was not the only source. I read about it previously from another article. In summary, gasoline engine will converge with diesel by next generation. Diesel engine will have to meet the same emission standard as gasoline engine and that does hurt efficiency.

http://www.popularmechanics.com/cars...nt-than-diesel

This is really mute point. We will all be driving some sort of hybrid system. I am quite interested in turbine engine + electric drive system. Turbine is more efficient but ramps very slow. Electric provides instant power. So use turbine to generate power for hybrid. That is the way to go. Electric power is really the next generation of performance automobile.

Who wouldn't want instant torque?

Do enough people on this forum do research before they blather about??

Engine efficiency

Engine efficiency with modern technology:
Gasoline: 25-30%
Diesel: 40-50%
Scuderi: up to 50%
Gas turbines: not very

Compression ratios:
Gasoline: 10-12:1
Diesel: 14-25:1

According to the www.fuelly.com data, which may be as good as any since it is reported using fill-ups and odometer readings, a 2011 335i gets on average 21.5 mpg while a 2011 335d gets on average 30.8 mpg.....

Even BMW's most advanced direct injection designs can't get away from diesel's superiority in the efficiency category. And if you believe the ham-fisted numbers the EPA puts up, which are shamelessly biased against diesels, I have a bridge to sell you....

So we can produce diesel from stuff other than fossil fuel, including recycled or biomass. By the way, where would we get the power to produce the electricity for the "future" electric vehicles?? Here is a way to actually compare vehicles for their total environmental effect, where electric vehicles wouldn't get away with being viewed as "no emission" vehicles.

Diesel is still a player and will be for a long time until answers to many questions are invented.

PL

Originally Posted by Pierre Louis

Do enough people on this forum do research before they blather about??

Engine efficiency

Engine efficiency with modern technology:
Gasoline: 25-30%
Diesel: 40-50%
Scuderi: up to 50%
Gas turbines: not very

Compression ratios:
Gasoline: 10-12:1
Diesel: 14-25:1



Even BMW's most advanced direct injection designs can't get away from diesel's superiority in the efficiency category. And if you believe the ham-fisted numbers the EPA puts up, which are shamelessly biased against diesels, I have a bridge to sell you....

So we can produce diesel from stuff other than fossil fuel, including recycled or biomass. By the way, where would we get the power to produce the electricity for the "future" electric vehicles?? Here is a way to actually compare vehicles for their total environmental effect, where electric vehicles wouldn't get away with being viewed as "no emission" vehicles.

Diesel is still a player and will be for a long time until answers to many questions are invented.

PL

I completely agree.

I have been keeping close track of the latest diesel vs GDI gasoline offerings in the same vehicle platform in Europe with equal or nearly equal performance (based on 0-100 km/hr times), and the diesel versions are still far ahead of the corresponding gasoline versions in nearly every case, even if you take the higher volumetric energy content of diesel fuel into account (0-100 km/hr times in parentheses)...


FUEL CONSUMPTION (NEDC Combined)


Audi A8 3.0 TDI Q – 6.4 l/100 km (6.1 sec) (27.3% lower FC)
Audi A8 3.0 TFSI Q – 8.8 l/100 km (6.1 sec)

MB S350 CDI BlueTEC L - 6.2 l/100 km (7.1 sec) (19.5% lower FC)
MB S350 CGI Blue Efficiency L - 7.7 l/100 km (7.1 sec)

BMW 640d – 5.4 l/100 km (8-speed auto) (5.3 sec) (28.9% lower FC)
BMW 640i – 7.6 l/100 km (8-speed auto) (5.3 sec)

Mazda CX5 2.2 SkyActiv-D – 4.6 l/100 km (Manual) (9.2 sec) (23.3% lower FC)
Mazda CX5 2.0 SkyActiv-G – 6.0 l/100 km (Manual) (9.2 sec)

BMW 125d M – 4.8 l/100 km (6.5 sec) (25.0% lower FC)
BMW 125i M – 6.4 l/100 km (6.5 sec)

MB C250 CDI Blue Efficiency - 5.0 l/100 km (7.1 sec) (25.4% lower FC)
MB C250 CGI Blue Efficiency - 6.7 l/100 km (7.2 sec)

BMW 520d – 4.7 l/100 km (8-speed auto) (8.1 sec) (26.6% lower FC)
BMW 520i – 6.4 l/100 km (8-speed auto) (8.0 sec)

BMW X3 35d – 6.1 l/100 km (8-speed auto) (5.8 sec) (30.7% lower FC)
BMW X3 35i – 8.8 l/100 km (8-speed auto) (5.7 sec)

BMW 740d – 5.7 l/100 km (5.5 sec) (27.8% lower FC)
BMW 740i – 7.9 l/100 km (5.7 sec)

BMW 530d – 5.3 g l/100km (6.0 sec) (auto) (30.3% lower FC)
BMW 535i – 7.6 g l/100 km (5.9 sec) (auto)

MB E250 CDI Blue Efficiency - 5.1 l/100 km (7.3 sec) (23.9% lower FC)
MB E250 CGI Blue Efficiency - 6.7 l/100 km (7.4 sec)

MB E350 CDI Blue Efficiency - 6.0 l/100 km (6.2 sec) (13.0% lower FC)
MB E350 CGI Blue Efficiency - 6.9 l/100 km (6.3 sec)

BMW X5 xDriveM50d – 7.5 l/100 km (5.4 sec) (40.0% lower FC)
BMW X5 xDrive50i – 12.5 l/100 km (5.5 sec)

BMW X5 40d – 7.5 l/100 km (8-speed auto) (6.6 sec) (25.7% lower FC)
BMW X5 35i – 10.1 l/100 km (8-speed auto) (6.8 sec)

VW Golf 2.0 TDI – 4.8 l/100 km (manual) (9.3 sec) (22.6% lower FC)
VW Golf 1.4 TSI – 6.2 l/100 km (manual) (9.5 sec)

BMW 535d xDrive – 5.7 l/100 km (8-speed auto) (5.5 sec) (28.8% lower FC)
BMW 535i xDrive – 8.0 l/100 km (8-speed auto) (5.8 sec)

(ave. 27.0% lower FC)


For reference, the National Academies conducted a similar exercise in 2008 and came up with a difference of 25.25% lower fuel consumption for the diesel versions than corresponding gasoline versions at equal or nearly equal performance (National Academies, “Assessment of Fuel Economy Technologies for Light-Duty Vehicles.” Table 5.A.1).

So the gap between gasoline and diesel really isn't narrowing much in most cases (i.e., diesel technology is improving as fast as gasoline technology).

I also agree on the well-to-wheels approach in evaluating the respective technologies. I compared a PZEV version of the VW Passat to the Passat TDI using both Argonne National Laboratory's GREET model and EPA's emission factors. The results may be surprising and can be found at http://webpages.charter.net/lmarz/emissions2012.html.

Thanks wxman

With due respect to those that like to race their cars 0-60 to the next stop light, it looks even better for diesels when compared just on the basis of low end torque, when you need to go to the higher powered V8 gasoline engines by the way I believe most of us really drive - in the lower RPM ranges. Then, a diesel engine gets upwards of 50% better fuel economy and costs a lot less to purchase and maintain. But I'm preaching to the choir here...

PL

One more data point to consider...

According to data provided by BMW in its "BMW Technology Day 2009 - EfficientDynamics" publication, the previous version of the 535i/335i gasoline engine (N54?) had a BSFC of 248 g/kWh. The current engine (N55?) has a BSFC of 245 g/kWh.

At the same time, the previous version of the 535d/335d diesel engine (M57?) had a BSFC of 205 g/kWh, while the succeeding version (N57?) had a BSFC of 197 g/kWh.

Thus, the BMW diesel engine technology has lowered fuel consumption by almost 4%, while BMW gasoline engine technology has reduced fuel consumption by a little over 1%.

I acknowledge that I'm not an engineer, but it appears that the gap between diesel and gasoline engine technology not only isn't closing, it's actually widening again, at least in BMW's case.

Originally Posted by Pierre Louis

Do enough people on this forum do research before they blather about??

Engine efficiency

Engine efficiency with modern technology:
Gasoline: 25-30%
Diesel: 40-50%
Scuderi: up to 50%
Gas turbines: not very

Compression ratios:
Gasoline: 10-12:1
Diesel: 14-25:1



Even BMW's most advanced direct injection designs can't get away from diesel's superiority in the efficiency category. And if you believe the ham-fisted numbers the EPA puts up, which are shamelessly biased against diesels, I have a bridge to sell you....

So we can produce diesel from stuff other than fossil fuel, including recycled or biomass. By the way, where would we get the power to produce the electricity for the "future" electric vehicles?? Here is a way to actually compare vehicles for their total environmental effect, where electric vehicles wouldn't get away with being viewed as "no emission" vehicles.

Diesel is still a player and will be for a long time until answers to many questions are invented.

PL

Here is a direct quote from the link you gave:

The gas turbine is most efficient at maximum power output in the same way reciprocating engines are most efficient at maximum load. The difference is that at lower rotational speed the pressure of the compressed air drops and thus thermal and fuel efficiency drop dramatically. Efficiency declines steadily with reduced power output and is very poor in the low power range - the same is true in reciprocating engines, the friction losses at 3000 RPM are almost the same whether the engine is under 100% load or not having any useful output on the driveshaft. The inertia of high speed gas turbine together with the low air pressure under low speed cause it to have a significant lag which many drivers are unwilling to cope with. Today the gas turbine is not used for automobiles and trucks because the usage patterns dictate varying loads, including idling speeds. General Motors at one time manufactured a bus powered by a gas turbine, but due to the economy where crude oil prices rose exponentially (1970's) this concept was abandoned. Driving comfort was good, but overall economy lacked due to reasons mentioned above. This is also why gas turbines can be used for permanent and peak power electric plants. In this application they are only run at or close to full power where they are efficient or shut down when not needed.
Gas turbines do have advantage in power density - gas turbines are used as the engines in heavy armored vehicles and armored tanks and in power generators in jet fighters.
One other factor negatively affecting the gas turbine efficiency is the ambient air temperature. With increasing temperature, intake air becomes less dense and therefore the gas turbine experiences power loss proportional to the increase in ambient air temperature

The key is that gas turbine is not good at powering varying load. If you use gas turbine instead to power an electric generator, then it makes a far more efficient hybrid system than current system. This was a concept proposed by Jaguar. How far does that make it? Its hard to say. Hybrid system is pretty much here to stay.

As for the discussion on diesel vs. gasoline, the expectation is that gasoline will gain HCCI technology in 10 years which will put it on the par with Diesel except for the energy differences. That is what the GM engine guy was saying. It is possible another diesel technology could help it improve.

As for the compression ratio, it has decreased due to direct injection. Again, this is from the same link.

"Diesel engines have a compression ratio between 14:1 to 25:1. In this case the general rule does not apply because Diesels with compression ratios over 20:1 are indirect injection diesels. These use a prechamber to make possible high RPM operation as is required in automobiles and light trucks. The thermal and gas dynamic losses from the prechamber result in direct injection Diesels (despite their lower compression ratio) being more efficient."

BMW 40d is rated at 16.5 vs. BMW N55 10.5. Currently, there is a thermal dynamic efficiency vs. diesel.

As for EPA, it does not discriminate against diesel since both engine runs at the same predefined pace and speed. EPA has down rate their setting from last time to reflect what most American do see in MPG. The down rating is based on secondary test they do for emission. That is why American MPG rating is so much worse than European settings.

http://www.fueleconomy.gov/feg/how_tested.shtml

EPA does discriminate against combustion engine vs. hybrid because they allow testing of hybrid when the battery is fully charge. That to me does not reflect reality. The electric number does not make sense to me.

As for the actual EPA rating vs. reality, that depends on your driving condition. For mine, I found it right on the dot for city. It rated my EPA at 19 city for 35D same as my last Honda Accord v6. In both, I have an average of 19 MPG. The diesel is expected to improve over time as it get more break in.

http://www.epa.gov/carlabel/documents/420r06017.pdf


Interesting analysis by the EPA on their mpg ratings versus real world for different drivetrain types. Page 16 of the pdf (page 8 of the report) has a nice table showing some results. From the article. Their own analysis indicates they underscore diesel more than other drivetrains:

As can be seen, diesels appear to perform the best with respect to their label fuel economy, outperforming the label by 4.3%. Conventional gasoline vehicles come very close to meeting their label, falling short by only 1.4%. Conventional vehicles with relatively high combined fuel economy (here assumed to be 32 mpg or more, representing the top 10% of conventional vehicles in terms of fuel economy) performed only slightly worse, falling short by 1.7%. Hybrids fall short by a much larger margin, 8.2%. Thus, the greater shortfall seen with hybrids appears to be more related to hybrid technology than to simply high levels of fuel economy.
With respect to the mpg-based label values, diesels still perform the best of the four types of vehicles, now exceeding their label values by 18%.b Those conventional vehicles with relatively high fuel economy fall next, followed by the typical conventional vehicle and hybrids. Thus, the YourMPG estimates indicate that hybrid performance differs from that of conventional vehicles, including those with high fuel economy.

Originally Posted by TDIwyse

http://www.epa.gov/carlabel/documents/420r06017.pdf


Interesting analysis by the EPA on their mpg ratings versus real world for different drivetrain types. Page 16 of the pdf (page 8 of the report) has a nice table showing some results. From the article. Their own analysis indicates they underscore diesel more than other drivetrains:

...

that report must have been the impetus for the 2008 changes, right? For pre-2008 MY fueleconomy.gov shows both original and revised EPA FE estimates.

Originally Posted by d geek

that report must have been the impetus for the 2008 changes, right? For pre-2008 MY fueleconomy.gov shows both original and revised EPA FE estimates.

That would have been good but the EPA lowered the numbers for all cars across the board in that change as I recall, making the numbers even more unfair to diesels. I know, because EPA mpg for my 2005 E320 CDI went down even though the original estimate was a bit low to begin with.

Only the 335d numbers seem close, but that may be because of the way these cars are driven - fast. The VW and Mercedes diesels seem to do much better than EPA implies.

PL

The 335d on the freeway seems to do better than the EPA figures. If actually going around the speed limit. It is the stop and go stuff that makes the mpg nose dive for me. I always have speculated this is because of how easily the small turbo kicks in. But I also speculate the turbo setup is what really makes the 335d such an enjoyable drive.