Prius loses out to VW on Autoweek mileage test

<div class='quotetop'>QUOTE(vtie @ Apr 26 2006, 05:03 AM) [snapback]245395[/snapback]</div>

That's a very misleading statement.

For a barrel of crude oil you'll get a certain amount of gasoline and a certain amount of diesel. For light sweet crude, it's about 10 gallons of diesel and 20 of gasoline. When you get one, you get the other.

BUT that doesn't take into account the fact that diesel is a much simpler fuel and requires much less energy to refine (fraction it off and you're pretty much done) than gasoline. Today, gasoline has evolved to be a really complex mix of loads of different chemicals with very tight tolerances on what works in modern engines / catalytic converters and what doesn't, and it takes a huge amount of energy to refine compared to diesel. This extra energy is rarely mentioned when people talk about gasoline.

<div class='quotetop'>QUOTE(vtie @ Apr 26 2006, 05:03 AM) [snapback]245395[/snapback]</div>

Crude oil at $70 per barrel is about $0.44 per litre, which is now more expensive than crude vegetable oil....

 

<div class='quotetop'>QUOTE(clett @ Apr 26 2006, 11:31 AM) [snapback]245396[/snapback]</div>

It's more intrinsic than that. Gasoline is a lighter fluid (and has less energy density for this reason). This is the major reason why diesels burn less fuel: it's more energetic. If you crack the raw oil, you actually get more gasoline.

<div class='quotetop'>QUOTE(clett @ Apr 26 2006, 11:31 AM) [snapback]245396[/snapback]</div>

That argument was valid for traditional diesels, but definetely not for modern turbo-charged common rail diesels. Diesel in Europe contails a *lot* of additives in order to accomodate for modern diesel cars. Most modern European diesels are known to be even more picky when it comes to fuel quality than gasoline cars.


<div class='quotetop'>QUOTE(clett @ Apr 26 2006, 11:31 AM) [snapback]245396[/snapback]</div>

That proves that a few countries are making a lot of money with the oil consumption, but it doesn't say anything about the environmental load of both alternatives.

 

<div class='quotetop'>QUOTE(vtie @ Apr 26 2006, 06:49 AM) [snapback]245403[/snapback]</div>

Diesel does have a higher energy density than gasoline, but gasoline engines use spark ignition and are limited to compression ratios of about 10:1, which means they are limited to about 25% efficiency. The Prius uses a Miller cycle to get 13:1 expansion ratio, but even that leads to only 33% peak efficiency.

The latest VW TDi diesels are at 43% efficient, so regardless of energy content of the fuel, a TDi extracts 30% more energy from the fuel than even the Prius engine. That's the main reason why TDi versions of the same model go on average 36% further per gallon than their gasoline counterparts, and only partly because there is more energy in a gallon of diesel.

As for cracking, that takes heat and more processing which takes yet more energy to make the gasoline.

 

<div class='quotetop'>QUOTE(clett @ Apr 26 2006, 01:35 PM) [snapback]245406[/snapback]</div>

Yes, diesels are currently more efficient in their combustion that gasoline engines. But that was not my point, I never claimed this. My point was that you should offset any gasoline-diesel comparison with the difference in energetic content between both fuels. Not doing this is simply unfair.

Another unfair comparison is that many people compare a Prius with an automatic gearbox to a Jetta with a manual gearbox. According to VW's data, the automatic gearbox consumes 10% more than the corresponding manual.

Take both into account and the numbers the Prius can present are impressive. Very impressive.

Apart from that, there are new developments in gasoline engines as well. The Prius engine is nothing special in any respect. New generations gasoline motors run on a "poor mixture" of air and fuel, and show an impressive decrease in consumption (e.g. VW's FSI engines) One example: a 90hp FSI gasoline engine is specified at 5.1l/100km on the highway, whereas an equivalent TDI engine consumes 4.3l/100km (only a 15% decrease). The poor mixture gasoline technology together with overcharging even holds more promise. Combine this technology with the advanced hybrid technology of the Prius and you have something really impressive.

 

<div class='quotetop'>QUOTE(vtie @ Apr 26 2006, 08:21 AM) [snapback]245413[/snapback]</div>

Not anymore... I think the new DSG automatic and the manual get identical EPA ratings.

 

<div class='quotetop'>QUOTE(Jonnycat26 @ Apr 26 2006, 05:05 PM) [snapback]245491[/snapback]</div>

My numbers came from today's VW web site, comparing the dsg gearbox to the 5-speed manual (93/116/EU averaged city-highway data)

 

<div class='quotetop'>QUOTE(vtie @ Apr 26 2006, 11:43 AM) [snapback]245516[/snapback]</div>

I see - 36/41 for manual and 35/42 for the automatic on edmunds.com

 

1 - TDI's don't typically get anywhere near their ideal MPG until they're broken in - which takes 50,000 miles or more

2 - How about the environmental effects of actually manufacturing each vehicle? And what's the service life of each once manufactured and on the planet?

 

<div class='quotetop'>QUOTE(fallingwindows @ Apr 26 2006, 02:24 PM) [snapback]245655[/snapback]</div>

I figured it would be something like that. I mean, how can a TDI possibly get better mileage than a Prius (even highway) when its EPA figure is 10 mpg lower? The EPA tests are very conservative and it's usually impossible to get better than them unless you go 60 mph or below on flat roads, yet people claim the TDI gets 50 mpg at 80 mph? I guess they neglect to mention you have to drive it 40,000 miles first (EPA tests, and all reviews of the car, are of course done at 10k miles or less).

 

Personally, I'm not impressed by any diesel car's gas mileage. Driving a diesel car is downright irresponsible these days.

Remember, the Prius was designed as a low emissions vehicle. The fact that it gets great gas mileage is nice but it's not why the car was designed.

If you think that a TDI gets better mileage, and you're content with the effects that driving a car like that has on the environment, then by all means purchase one. But when you buy a Prius, you can both save money at the pump and also do your part to help the environment and your children. You may (but probably won't) save $50 a year on gas with a TDI over a Prius, but the environmental impact of the car is far more than $50/year.

If the Prius were not available, I still would not consider buying a diesel to save money on gas. I'd pay a little more for gas and keep my lungs and the lungs of my neighbors a little cleaner and buy something that uses unleaded gas. But this is just my opinion, yours may differ. Some things are more important than money, at least to me.

 

<div class='quotetop'>QUOTE(finally_got_one @ Apr 22 2006, 10:28 PM) [snapback]243840[/snapback]</div>

Hello, I'm new here. I was impressed by this civilized, balanced discussion, and the remark above is especially meaningful today. I hope people can try harder to save some fuel, and when they get serious the declining demand will bring down the prices. I am a "diesel-head" that drives very carefully-- mostly that means not going quite so fast. To encourage others, I am now reporting the mileage on my last tank with my signature. My current report is for a trip from near Salt Lake City to Fresno, average speed about 65 mph. This is mostly highway driving except for perennial traffic jams through Las Vegas. Driving conditions were favorable except for strong headwind across the California desert.

Ernie Rogers
__________________________________________
| DRIVING FOR EFFICIENCY
|
| April 22 2006: 784.0 mi. / 12.18 U.S.gal = 64.3 mpg
| 2003 Beetle TDI (MAX MPG)
| B5 5% Biodiesel blend
| Michelin Energy tires
| Motul Specific 506.01 motor oil
|_________________________________________

 

Please.

Its a VW. Probably one of the most unreliable cars companies around these days. And it uses diesel not gas. And it is less green. The resales is not as good, at all. The the engine knocks and smells funny. The prius is way closer to a lux car.

Who cares if it get better milage in some situations. That is all it has. Reliability is a deal breaker as it impacts resell and ownership exerience. Only if I lived in a very cold environment would I consider one.

 

You're right. VW produces more lemons -- at least for the US market -- than anybody else. Buying a VW when you live outside of Europe is quite a gamble.

 

My "real world" is 53 now and I expect to rise to 55-56 in the summer. There is NOTHING more real than that.

 

I did not read the entire thread, and apologize if this has been brought up --

In the case of the Prius, FE was calculated by 'filling up' the tank at the start and end of the drive. If they had asked any Prius owner, they would have known that is simply too inacurate a method to use, and the results are useless. They *did* mention that the tank MFD was between 45 - 46, but decided to disregard that datum <<shrug>> as less useful.

They drove 75 - 85 mph, and at that speed 45 mpg is just about right. They are quick to jump up and down in ecstasy that once again, the Prius cannot come close to EPA, but this is BS. EPA testing is not done at 80 mph, but about 60 mph. Getting excited that MPG goes down at high speeds is not a revelation.

The diesel results 20% greater than EPA are interesting, but I am extremely sceptical. In order to be true, the tdi would have to run it's engine with an efficiency at 80 mph that much greater than 60 mph to cover the 20% improved result AND overcome the 16/9 X increased air resistance.

I was reading one of the tdi forums last night that focuses on fuel economy. Number one advice ? SLOW DOWN to around 60 mph !! So the tdi gurus say that EPA highway cycle should yield optimal results, but the C&D guy does a whole lot better at 80 mph ?!

huh

I'd say it is pretty clear that the tdi and Prius are ballpark equivalent MPG highway cars with a nod to the tdi; that the Prius is ~ 50% better MPG in congested/stop & go driving; and in terms of noxious emissions, Prius is PZEV, while tdi is about twice as bad as LEV -- about a 2 - 10 x difference, depending on toxin. Beyond that, there is subjective preference.

 

<div class='quotetop'>QUOTE(EricGo @ May 6 2006, 05:16 PM) [snapback]250858[/snapback]</div>

That's not true; the EPA highway test is not done at 60 mph. It's done at varying speeds between 24 and 60 mph, with an average speed of 48 mph. Actually driving at a fixed speed, either at 48 or 60 mph, always results in higher mileage than the EPA highway figure because they change speed often, i.e. by accelerating. At least that's how I understand it.

It does seem suspicious to me that people exceed the EPA figures so largely in the TDI but maybe the car gets horrible mileage when accelerating? Also some people say you have to drive a TDI 50,000 miles to start getting good mileage, or something stupid like that, but obviously the cars the EPA tests are new.

 

The HWFET cycle is a chassis dynamometer driving schedule, developed by the US EPA for the determination of fuel economy of light duty vehicles.

The following are some characteristic parameters of the cycle:

* Duration: 765 seconds
* Total distance: 10.26 miles (16.45 km)
* Average Speed: 48.3 mi/h (77.7 km/h)

 

<div class='quotetop'>QUOTE(EricGo @ May 6 2006, 05:16 PM) [snapback]250858[/snapback]</div>

Actually, there are more than a few TDI drivers who routinely beat the EPA estimates.

There were 23 drivers that broke 50 mpg in April in the monthly fuel efficiency competition. Three broke 60 mpg.

 

Iv'e even thought about buying a diesel over a prius. The only reason I want the diesel is because I have an unlimited supply of free diesel to me.

 

<div class='quotetop'>QUOTE(SyZyGy @ May 7 2006, 09:42 PM) [snapback]251271[/snapback]</div>

One idea I could stand to see Toyota and VW look at would be the idea of putting a TDI engine in a Prius, and see what that setup gets. I would not be surprised if the current EPA testing methodology yields 75 mpg or more as a diesel hybrid. And with emissions being regulated on a per-mile basis, reducing fuel consumption overall should yield a straight-line corresponding reduction in pollutants emitted.