Skip to main content

Why can't the 2015 Mazda 6 diesel work in the US?

Mazda fans in search of a diesel will have to wait a little longer. Could it be that the Mazda 6 diesel is not green enough or efficient enough to beat the gas version?

Mazda announced today the Mazda 6 diesel, which had been scheduled for introduction here in the coming months, is not coming to America now, and Mazda does not have any timeline for the car to be introduced here. As an explanation Mazda said that “…the launch of its SKYACTIV-D clean diesel engine in North America is being further delayed from its Spring 2014 announced debut timing…it was decided that further development is required to deliver the right balance between fuel economy and Mazda-appropriate driving performance.” With regard to when the car might be ready Mazda says “Further information on the program, including a timeline of launch for North America, technical specifications and fuel economy will be available at a later date, closer to launch.” Something’s up and Mazda does not want to say what.

The current 2014 Mazda 6 sedan achieves an impressive highway mileage of 40 MPG with its gasoline engine. Its overall 32 MPG rating is also great for a relatively large family sedan. While not really a fast car, the automotive press is overwhelmingly impressed with the car and it is often cited as the best car in its class for enthusiasts. That class is four cylinder affordable sedans, not sports sedans. However, about a year ago word got out that Mazda had a great diesel engine that could make the Mazda 6 one of the most fuel efficient non-hybrids in America if it were introduced here. Mazda also took the diesel racing to keep fans interested, further develop the engine, and to keep the car in the headlines.

Mazda wants to market the diesel as a green car, and in fact calls it the “SKYACTIV-D clean diesel engine.” However, as we have often reported here there is no basis for diesels to be called clean or green. With regard to the green claim, diesels don’t emit less CO2 per mile than do their gasoline counterparts in the market. The 2014 Passat Diesel automatic can achieve 40 MPG highway and 34 MPG combined. It produces 290 grams of CO2 per mile, while the gasoline Mazda 6 automatic produces just 275 grams of CO2 per mile. So if diesels put out more greenhouse gasses it is hard to call them green cars. Furthermore, in each barrel of crude oil refiners can produce about 19 gallons of gasoline compared to about 11 gallons of diesel. Therefore, more oil is needed per mile to propel a diesel car. More oil used and more CO2 produced does not equal green.

We have also compared the cost per mile to drive a diesel versus a gasoline car and have found that in family cars the gasoline cars are less expensive. Diesel engines do sometimes have a slight edge in mileage over contemporary gasoline engines, but the fuel costs more. Typically diesel costs about 10% more than regular gasoline, which is what almost all mainstream passenger cars use today. More CO2, more oil used, and more expensive to drive is hardly a recipe for widespread success. Hopefully we will find out at some point exactly what the Mazda diesel can really do, but for now Mazda does not even have a launch date.

Mazda’s new diesel may be slightly more fuel efficient than Volkswagen’s but we have no US based test evidence that it is. Volkswagen has had the most experience with diesel vehicles in America in terms of number of models, years produced, and units sold. Mazda’s comments about the diesel not yet having the right balance of “fuel economy and Mazda-appropriate driving performance” makes us wonder if the car can’t beat the gasoline car’s already excellent efficiency and CO2 emissions.

Related Story:
2015 Volkswagen Golf TDI vs. Toyota Corolla LE Eco – Efficiency meets economy

Photo of 2014 Mazda 6 courtesy of Aaron Turpen.


Aaron Turpen    January 9, 2014 - 2:20PM

Actually, they've had issues with the European version being problematic. I think this is really about not wanting to introduce a total flop to the NA market and ruin the momentum they're building as a brand.

Carlos (not verified)    January 10, 2014 - 3:04PM


Your point:
"Furthermore, in each barrel of crude oil refiners can produce about 19 gallons of gasoline compared to about 11 gallons of diesel. Therefore, more oil is needed per mile to propel a diesel car. More oil used and more CO2 produced does not equal green."

This is a completely pointless statement. If your processing a barrel of crude oil for 19 gallons of gas, the 11 gallons of diesel is still produced from the same barrel. Are you saying that processing a barrel of crude for just 19 gallons of gas is more green then producing the same with 11 gallons of diesel?

This entire article seems to be a diesel bash session with a lot of personal views and very few actual facts.

David Lapp (not verified)    July 27, 2014 - 3:37AM

In reply to by Carlos (not verified)

Unfortunately, I think the issues of refining motor fuels from crude oil are misunderstood. It is not possible to produce only diesel or only gasoline fuel, both result from refining. It is possible to tilt the ratio and produce some more of one or the other, but there are limits as to how far the ratio can be moved. In Europe, the usage of diesel is about half, across all the countries (from info I saw some years back), but varying widely from country to country. In USA, the diesel percentage in passenger cars is much lower, somewhere around 3 or 5 percent. Of course, more diesel is used in USA for over-the-road trucking than in Europe (due to the much greater distances).

Pressure combustion has traditionally offered somewhat greater efficiencies (about a 15% advantage) for diesels. Attempts to utilize pressure combustion for gasoline cars has been problematic and not very successful. However, it seems that technology such as direct injection, variable valve timing, etc has achieved much of the advantage, so diesel engines may have less of an advantage than previously.

It is incorrect to say that diesel production requires more feedstock. Probably, the opposite is true, there are likely greater losses in cracking to get more gasoline (and also probably more energy input, also offsetting total energy efficiency). What is true to say is that there are limits as to the availability of either fuel, depending on refining ratios and overall demand. I am not a fuels producer insider, so I don't know where those limits lie and thus how many more diesel passenger cars could be accommodated with current refining plants and demand. Likely a (knowledgeable) person from the industry could answer this question relatively easily.

John Goreham    July 27, 2014 - 1:56PM

In reply to by David Lapp (not verified)

David, great comments. On the web there are articles from oil companies an individuals I feel answer the question. I simply compiled those and built them into the stories. I provided links in the base stories. I did a lot of reading on this on petroleum producer's websites and also on those that follow the topics. I agree with what you say, except that in the US, from my research findings, it does seem that if we switched a significant amount of cars to diesel it would mean that refiners in the US would have to change the refineries significantly. The equipment and process required changes when the refineries change what they want to produce, They don't simply "decide" what to produce (I think you know this , so I'm not trying to be condescending). Those refiners are also closely monitored and don't like change because it invites more regulations. If the US decides to move toward significantly more automotive use of diesel it sure seemed to me that more crude oil would be required to meet that demand. We now import oil in the US and concurrently we export refined gasoline. When I looked at this closely it was pretty clear that we in the US consume all the diesel we now make (refine). Much of it as home heating oil. Much of it as truck fuels. I found no indication we were exporting diesel. To make more means more oil will be used. As I have said many times, there is not one single example of a US-market diesel family car that is more efficient on the EPA combined cycle than the gasoline family cars in its class (meaning affordable, made in high volume). So why would we ever change?

John Goreham    January 10, 2014 - 7:08PM

I see your point. And to strengthen it I will say that in other markets refiners do get more diesel from a barrel than US refiners, though it never exceeds about 25%-25% (the rest is other stuff). My point is that here in the US, we already use all the diesel we produce. If one goal of moving towards a greener way of life is to use less oil (and I think that is a fair statement) switching to a fuel that has a lower yield per barrel of black gold, Texas Tea, is not heading in the right direction. Let's take my opinion out of it. How is a car that cannot even emit less CO2 than a regular, non-hybrid gas car green? So far there are no examples in the US market where any affordable diesel can beat the regular gas cars. The hybrids simply stomp the diesels in CO2 grams per mile and MPG. Then there are the EVs... I am HUGE Mazda fan. That bias I will not dispute.

John Goreham    July 11, 2014 - 4:13PM

In reply to by Michael Reiche (not verified)

The point I was making had to do with domestic production versus domestic consumption. Oil companies produce goods for export. The reason for this is to make profit. For example, the United States exports gasoline. The point is that switching to diesel in the US market would not reduce our "dependence on foreign oil." So, since it costs more, we have to import it, does not offer any reduction in CO2 production, and it does not provide better mileage in family cars, it is sort of hard to argue it makes sense. The story points out that Mazda has struggled to find a way to make the diesel work in the US market.

Michael Reiche (not verified)    August 19, 2014 - 7:11PM

In reply to by John Goreham

"How is a car that cannot even emit less CO2 than a regular, non-hybrid gas car green?"

The diesel Mazda6 emits less CO2 (108 g/km -> 172 g/mile) than the gas Mazda6 (275 g/mile)

mazda uk -> /aboutmazda/news/technology/when-size-doesnt-matter-with-co2-emissions/

That's the problem with comparing apples to oranges - or Mazdas to Passats

John Goreham    August 20, 2014 - 10:27AM

In reply to by Michael Reiche (not verified)

You are comparing the European (British) test cycle (Called Official Test Cycle) to the US EPA test cycle. The two testing protocols are not the same, and the European is always more generous. Use examples from the same test in the US and tell me what you find. Note too in your source from 2013 Mazda says the Mazda6 D "Mazda6 CO2 emissions start from as low as" Start From as Low as means that they used the best case scenario, not the combined EPA CO2 standard test. Remember, the point of the story was that for some reason Mazda planned to introduce the Mazda6 D here in the US, but then did not. Argue theory all you like. You could be right some day. For now, in the US, the diesels test out as producing more CO2 than regular gasoline engines in the same EPA class (same size and weight vehicle). The hybrid gasoline engines are dramatically lower than the diesels with regard to CO2.

Max Looker (not verified)    January 22, 2014 - 6:04PM

It's all about how the engine's get those high mileage number. In real world driving, it's much easier to get high mileage from a diesel than the traditional gasoline engine, or even a hybrid. I am experienced at hypermiling, and I can beat EPA ratings in almost any vehicle. What I've learned is you have to consciously be thinking about your mileage to do well in a gasoline car, hybrid or not. In a diesel it just sort of happens like an accident of nature. The penalties for both high speed cruising and heavy-foot accelerating are mysteriously minimized.

The driving characteristics of diesels are very different compared to naturally-aspirated gasoline engines. The HP-Torque relationship in diesels makes them feel fast without needing to be fast, which facilitates engine downsizing very well. Mercedes has put their Bluetec 2.1L I4 in many vehicle that would have traditionally have detuned NA V8s.

What makes diesels green is primarily the relative simplicity of making biodiesel from natural fats. Also, when a diesel engine is hyper-miled the benefits are astounding. The Passat diesel you mention rated at 43 MPG highway set a world record for best mileage while driving through all the lower-48 states with an AVERAGE MPG of 78 MPG.

Aaron Turpen    January 23, 2014 - 10:33AM

In reply to by Max Looker (not verified)

The exception, Max, is high compression gasoline engines. These are very similar to diesel and thus achieve the same basic MPG per dollar spent on fuel. Even, as you say, driving at high speed or in a less than eco-friendly manner means good economy. I noted this in the Mazda6 SKYACTIV with iELOOP. The SKYACTIV system is running at a compression ratio between 13-14:1, depending on the engine size. Ford's EcoBoost runs at about a point lower, between 12 and 13. It's this compression that tends to remove much of the variability from fuel usage.

I will agree to the easier biofuel options diesel offers and have talked about that a lot. In addition, the glycerol byproduct of biodiesel can be made into bio-gasoline. Methanol is another oft-overlooked fuel.

daniel Contreras (not verified)    May 22, 2014 - 10:27PM

Did he really compare a passat diesel to a gasoline mazda. Why not compare both the diesel and the gasoline Passats, this whole article is trying to bash on diesel. Neither is a greener fuel, however diesel can produce alot more power in less consumption than gasoline.(higher mpgs) Oil comps dont want diesel to become mainstream.

Aaron Turpen    May 23, 2014 - 11:00AM

In reply to by daniel Contreras (not verified)

You obviously don't know a whole lot about diesel. Do you realize that it requires MORE oil to make a gallon of diesel fuel than it does a gallon of gasoline? And that nearly all diesel cars do not allow biodiesel and will void warranties if you use it because of uncertainties about its cleanliness? It's time for you to drop your conspiracy theories and read up on some actual facts about fuels.

Michael Reiche (not verified)    July 11, 2014 - 2:39PM

In reply to by Aaron Turpen

" it requires MORE oil to make a gallon of diesel fuel than it does a gallon of gasoline?"

You make it sound like the residual oil is discarded. It's not. It's used for things that are more valuable that fuel - and therefore diesel fuel is the better of the two.

John Goreham    July 11, 2014 - 4:15PM

In reply to by daniel Contreras (not verified)

I compared the car that the story is about (the Mazda6) to the only diesel car in its category, the Passat. At the time of this story's publication VW didn't have any gasoline engines that sold well in the US. Their poor fuel economy compared to the leaders in the class could be one reason.

John Goreham    August 16, 2014 - 9:40AM

In reply to by Michael Reiche (not verified)

Thanks for pointing that out. That may have been unclear. Here is what I mean. VW does not sell a single automobile in the US market that is anyplace close to popular in terms of sales in its class. Ford, Honda and Toyota make cars in the class that the Passat tries to compete in. Each of those cars (Fusion, Accord and Camry) outsell the whole VW brand. VW does not offer competitive gasoline-powered products in the US market, and the engines are a main reason why they are not competitive. The GTI is a wonderful car and its engine matches its personality perfectly, but it has never been a leader in fuel economy. Even that car is not a sales winner. Just for comparison - Toyota sells about as many Plug-in Prius cars each month as VW does GTIs. Which is to say, barely any, by comparison to mainstream models. - When VW boasts that its diesel sales "Are up 20%" or whatever, it does not matter, because the brand's overall sales are terrible. Low, and trending lower each month, as the rest of the brands grow. - Sorry to say negative things about VW, but this is not opinion. VW's total sales were 30,553 vehicles in July. Down 14%. Just to say it plainly, if the Passat's sales are 23% diesel (so under 2,000 cars) , that means that practically speaking, almost nobody is buying a Passat diesel. The Camry outsells it by roughly 20 to 1 - and the gap is getting bigger. Camry sold 39,888 units in July. Up about 10%.

John Goreham    May 23, 2014 - 8:26AM

The Mazda6 is a leader in fuel efficiency among gasoline powered cars in its class. The gasoline powered Passat is not now, and has never been. It is hard to point to a good example of a class leading gasoline powered German car. That is changing. VW is going strongly into hybrids and plug-in hybrid gasoline cars. The reason is that diesel outputs more CO2 per mile than gasoline cars do and gas hybrids are significantly lower. The European markets are going to start to move away from diesel due to their carbon regulations. I am fan of Mazda and hope the diesel car does someday come and show some impressive fuel economy and performance numbers.

Michael Reiche (not verified)    July 11, 2014 - 2:41PM

"Diesel engines do sometimes* have a slight** edge in mileage over contemporary gasoline engines"

sometimes* - always
slight** - 30%

John Goreham    July 11, 2014 - 4:08PM

In reply to by Michael Reiche (not verified)

Please provide your specific examples of diesel cars that lead their size category in fuel economy. Maybe you can find some truck or sports/luxury examples where this imaginary 30% diesel advantage is true, but in the family car category the VW Jetta Diesel's engine has no edge over the Toyota Corolla LE Eco gasoline engine, or the Nissan Sentra's. These are the two sales leaders in that category. In the larger category that the Mazda 6 falls into the VW Passat Diesel has an EPA rating of 34 combined and the gasoline Mazda 6 rates 32 MPG. They have the same highway mileage. My examples are taken from and are in the body of the story. The 30% number you cite is the diesel lobby's talking point. It is not based on any affordable cars for sale in the US market. I asked them.

John Goreham    August 16, 2014 - 11:04AM

In reply to by Michael Reiche (not verified)

How come you did not pick the most fuel economical gasoline Chevy Cruze for your comparison? The 2014 Chevy Cruze Eco (gasoline-non hybrid) matches the diesel at 33 MPG combined. 31MPG when it is an automatic. Link here.

Michael Reiche (not verified)    August 19, 2014 - 6:53PM

In reply to by John Goreham

"How come you did not pick the most fuel economical gasoline Chevy Cruze for your comparison?"

Because there is no equivalent Chevy Cruz Eco Diesel. You can read the MotorTrend article to see what changes the Chevy Cruz Eco has (180 lbs less, low resistance tires etc.)

Sill - the Chevy Cruz diesel gets 6% better fuel ecomony (33 vs 31mpg) when compared to the Chevy Cruz Eco with the same transmission.

John Goreham    August 16, 2014 - 9:45AM

In reply to by Michael Reiche (not verified)

I'm sorry I don't agree with your premise. VW simply does not have a modern, competitive gasoline Passat for us to compare to its diesel. The whole point of the EPA,, the Monroney sticker, and all the other ways we compare cars that are the same weight and size is to show which manufacturer offers the best fuel economy in the class.

Michael Reiche (not verified)    August 19, 2014 - 6:36PM

In reply to by John Goreham

John, I understand that you disagree with me, but could you show some data that disagrees with me?

"VW simply does not have a modern, competitive gasoline Passat for us to compare to its diesel"

What about Chevrolet? Audi? Mercedes? BMW? Jeep? Porsche?

VW Passat (36%)
Chevy Cruz (22%)

2014 Audi S5 - 29mpg vs 22mpg (32%)
2014 Mercedes ML350 - 23mpg vs 19mpg (21%)
2014 BMW 328 - 37mpg vs 27 mpg (37%)
2014 Jeep Grand Cherokee 2WD - 25mpg vs. 20mpg (25%)
2014 Porsche Cayenne - 23mpg vs 17mpg (35%)