Top 25 High MPG ICE/Diesels (any Prius Killers?)

35 mpg EPA sounds about right to me, but it is still a hard target since combined MPG is required and most Americans do not want to run around in an iQ or even a Yaris.

 

The most fuel efficient vehicles - Spritmonitor.de

Not quite comparing apples to apples, is it?

 

We have some data from the efficient car contests. For very light cars less than 1800 lbs the regen isn't all that important versus the weight. A hybrid can downsize its engine though and use electricity. In the city the phev or bev wins. The hybrid by using battery power in these low power modes wins. The low load efficiency of a diesel gives it an advantage over a gasoline car in the city all things being equal. The heavier the vehicle, the more the diesel helps, which makes it a good choice for heavy SUVs and Trucks.
Compare Side-by-Side

Note diesels do better in the real world than on EPA tests, as you can see from the self reporting. The jetta is one of the few cars with all of the choices, and adjusted for energy content on the epa the hybrid gets about 50% better milage than the diesel.

Again, you are seeing a difference in vehicles not power train. In europe you will see aero choices, but not in the US.

 

That is just a little more work than I have energy with a number of technical issues:

• Fuelly.com - would be the place I would start but only statistically significant samples, over 32.
• Handling min, avg, max - the distribution is a challenge.
• Self-selection urban vs highway
• Normalizing weight or payload volume

I have no problem if someone else wants to do the study but the EPA numbers are:

1. Standard protocol - removes a lot of variables
2. Allows low-volume vehicles into the analysis (aka., new Honda Accord hybrid)
3. Easy to find - it took less than 30 minutes to gather and plot the data
4. Model years 2013-2014

Sounds like an opportunity if someone has the time. <grins>

Bob Wilson

 

Even via the new EPA it'd still do about 60mpg
But as stated above, folks like more room.
.

 

I absolutely agree here, and in the jetta vw seemed to get about 50% more mpg in the city with hybrid versus diesel (when diesel fuel content is included in the calculation) I am just saying it is significant, but likely not as big as that difference. For long highway commuters, CR 65 mph (ignore their city, it awful) and car and driver 75 mph test are good places to start.

Absolutely, but as I had pointed out in another thread the city cycle approximates driving in the 1960s in LA, which doesn't really approximate many of our experiences in 2013. I simply think you need to note the skew. Car and driver or motor trend did a take down of many of the self reporting diesel drivers, but noted there is some difference. They tried to get around it by testing on the same day same conditions. Each of us has different real world. Many manual diesel drivers hyper mile as much as prius drivers, but techniques are different.

 

The EPA actually has done some of the work already.
Diesel mpg underrated on the window sticker | PriusChat
They know their methods are under reporting what a diesel returns. For the lazy, just increase the EPA numbers by 10% or 15%. The values will still be on the conservative side.

Another interesting tidbit from the surveys used in that study, most people report their city to highway mix as 42% to 57%, or at least around there. It is also the split the EPA uses for other programs, and yet the combined on the sticker is still 55/45.

As for gas and diesels lower city numbers, drive train inefficiencies are only part of it. Unless, the inability to turn off the engine at a stop falls under the inefficiencies umbrella.

 

The 30% "rule of thumb" just acknowledges that diesel fuel has 30% more energy content per gallon (from higher carbon content) than gasoline. Other variables (ICE efficiency ... ) cause the usual YMMV comment.

JeffD

 

Where did that 30% come from?
Using 116090 btus/gal for gasoline, and 129488 btus/gal for diesel, the difference is no more than 12% depending on how do the math. I know wikipedia can be off, so are those values correct.

Bob's plot is just the window sticker values. The EPA study I linked in the other thread stated that reported diesel economy was 18% over the new window sticker values(this study was for the changes that happened in 2008). A recent comparison of the reported Fuelly average for the Cruze diesel was around 30% higher than the EPA combined, IIRC.

 

maybe from using higher compression?
.

 

The Diesel's higher compression does increase it's efficiency over a normal gasoline engine, but so does our Atkinson/Miller cycle engine in our Prii.

JeffD

 

It will vary by specific engine model, but diesels are still more efficient. An Atkisonized petrol still has a throttle plate and tighter range of air:fuel mixtures. Of course, the leaner mixtures are why diesels are NOx producers.

 

Based on the EPA "combined" mileage (unrounded values), the relative difference between diesel and gas versions of the same vehicles is almost exactly 30%, assuming my calculations are correct (29.2% better to be more exact; ~31 mpg average for diesel versions, ~24 mpg for gas versions, overall average).

According to the FE values reported on Fuelly, the average mileage of the diesel version of the Passat is about 55% better than the 2.5 liter Passat gasser, while the EPA relative difference is about 36%, lending more credence to the unrepresentative values reported by EPA for diesels.

 

You can remove the throttling losses is by applying variable lift to the valves like mazda does in skyactiv. The throttle is wide open in most circumstances. Anouther technology that can be tranfered is di. Key to gasoline ice efficiency is load, as they are most efficient at higher loads, which means the high gear count transmissions (6+, cvt, or ecvt) are needed to keep the ice in an efficient range. Diesels are most efficient at around 60% load, but stay quite efficient in lean mixtures, giving them an advantage when power is only needed occasionally.

 

Hey folks, take a chill pill:

1. Proposed 'correction factors' - I've seen these ever since my first Jetta TDI vs Prius study: These are user reported MPG reported at the EPA web site. What we found is a normal distribution with the Jetta TDI significantly lower (48-41)/48 ~= 14.6% lower, across the board. I'm sorry but diesels are not as efficient as a full hybrid because the hybrid will turn the engine off. The diesels continue to 'idle' burning fuel to overcome their engine overhead, the internal friction of their moving pistons, valves, and valve trains. In contrast, the hybrid just turns that nonsense off every chance it gets along with a very efficient engine.
2. Proposed 'methods' - would you prefer Consumer Reports, Car and Driver, or Green Human (advertising agency)? If I have a choice between a documented methodology, something resembling an engineering test, over some 'sweet sounding' source pandering to my prejudice, I'll take the engineering test. Others are welcome to use the alternatives. But I still remember the shock and disappointment of those who bought Belt Assisted (BAS-tard) hybrids in the mid-2000s. In effect, one major car maker charged thousands of dollars for systems that at at best were MPG rounding errors.

If you want to make a competing graph, one that meets your expectations, go for it. There are plenty of ways and approaches but don't skimp. If you want to apply a correction factor use 100% and make the diesels or even gas cars hugely better than the hybrids. If you want to fool yourself, go for it but I can't do that.

Now it so happens there is one EPA data set, the one that includes the CAFE number, freely available for download. This overcomes the manual, data entry problem and provides a rich source of ancillary data such as weight and displacement. This data includes the roll-down coefficients I use for vehicle drag and power modeling:

This is how I knew the CMAX 47/47/47 did not make a lick of sense. But in terms of priorities, I have a full plate of interesting technical problem.

Bob Wilson

 

I was never trying to claim that a diesel could beat the Prius. Just that their EPA window sticker numbers underrate what they return on user surveys. For 2006 models, the user reported(off EPA site) average for the Prius is 3.7% better than the 46mpg combined sticker value. For the Jetta it is 24% better than the 33mpg combined.

That's with the numbers adjusted for comparison with the 2008 testing results. With their original values, the Jetta is only 11.6% better for reported users than the sticker, but for Prius drivers the results are 13.5% worse.

While the regulations require tweaking in light of what Ford did with the Fusion hybrid and C-max, the adjustments made in EPA testing for 2008 onward generally seems to give a better estimate of what a gasoline car will return in the wild, it doesn't for diesels. In fact, the discrepancy got larger.

I believe hybrids and diesels can both play a part in reducing fuel usage. For diesels to have a fair shot in the market, the info presented to consumers needs to be equitable to what is given for petrols and hybrids.

 

It seems people who are pro diesel vs hybrid, don't spend much time thinking about the extra cost of diesel as a fuel and that diesel cars cost more to service and if something breaks like turbo or injector pump it gets real expensive quick. Don't get me wrong diesel engines work well for hwy mpg. and they get very good mpg with heavy cars. I guess that is why I never have seen a gas engine in a big truck.

Diesel hybrid may be a good system, but I don't know if turbo cool down and heat back up with engine going on and off would work out.

so as a former diesel pickup owner, I thought it made more sence to replace my f350 4x4 diesel with a f250 4x4 v10 gas. I am happy with my decision because gas cost less, I get 12 mpg hwy towing my 34ft fifth wheel and this is the same I was getting with my diesel. I must admit the v10 in town mpg is terrible about 7 mpg. and my diesel was about 16. I don't know why that v10 uses so much fuel without a load. I bought a gague that show instant and trip mpg. that thing uses a lot of fuel at low speed even without much load. The only thing that helps mpg is get it up to hwy speed, load or not and you can get 12 most of the time.

 

For the record, I am not diesel vs hybrid. I am pro for both. They both have strengths and weaknesses. Hybrids are generally best in the city, but can do well on the highway. Diesels do well on the highway, and they are also good heavy vehicles and those that do work. Which can lead us to a discussion on why cars don't tow ratings in the US.

The extra cost of diesel is a reason enough to change the EPA testing and/or labeling for diesels. With lower numbers posted than what a driver will typically get, the costs of the diesel will be artificially inflated. Using erroneous numbers could lead a person to getting a gasoline version instead, and end up burning more fuel and cash than if they got the diesel.

Despite the under rating of the fuel economy numbers, a study comparing gasoline to diesel options within a model(not against a generic gas car or a hybrid) for the TCO(price, fuel, insurance, repairs, resale,etc.) was lower in most cases for the diesel.

Large trucks mainly use diesel for the low end torque. It is needed to get heavy loads moving. Low end does mean less rpm, so less fuel. If there was a gas engine that had the same economy and torque output, it would have a shorter life due to the higher rpms.

The Volvo plug in was more popular than expected. We should see data on maintenance and repairs from them in the next few years. The real hurdle for a diesel/electric hybrid will be cost. It will be more than a gas hybrid or diesel alone.

If in town means lots of stops and coasting, the diesel will do better because its idle consumption is tiny. What year and transmission is it. DFCO might be near non-existent, and an automatic might not lock up at low speeds. My friend had the V10. They are supposedly known for breaking spark plugs. Some had to be replaced every two years for him. Might want to check them.