Economy-minded drivers consistently get well over 50 MPG on a TDI like mine ('96-'97 VW Passat). I don't give a second thought to driving economically -- brisk acceleration and 80+ miles per hour on the highway is a daily habit -- and I still get 43.0 MPG average. For a car of its size, weight, and performance, that's still pretty **** good, and is still better than the original (pre-2008) EPA combined rating of 42 MPG (38 city/47 highway). And with its 18.5 gallon tank, that means well over 700 miles per tank, which is my favorite part. A Prius might give me slightly better mileage overall, but its puny 11.9 gallon tank would definitely mean more frequent stops for fuel.

p.s. Wow, this is the first forum I've been on where I'll have to change "d a m n" to "darn" to get past the bad-language filter.

 

In North America, only 11.2-11.5 gallons is usable due to a sophisticated vapor capture system. Over filling is risky and can result in a pretty expensive fuel tank replacement ... not a warranty item.

We also have moderators intolerant of SPAM and abusive postings. Folks don't have to agree, opinions are welcome, but the tone needs to be civil and professional. Facts and data outweigh invective any day. Welcome to GreenHybrid.com.

Bob Wilson

 

If we say the tank holds 11 gallons, and estimate the Prius's mileage at 45 mpg, the range is still around 500 miles. At 70 miles per hour that amounts to about 7 hours of non-stop driving. How big is your bladder?

I like to stop every couple of hours regardless of the need for fuel.

 

My Passat's tank is actually around 20 gallons when you fill it up to the brim. The vestigal vapor recovery system -- not needed with diesel fuel -- limits its capacity to 18.5 gallons. But I'm in NJ where full-serve is mandatory, so I just let the pump jockey do the normal routine instead of trying to top if off every time. Anyway, my largest fill-up was just over 18 gallons, and that got me over 800 miles of driving range on that tank. If I played it safe and only tried to squeeze 10.5 gallons of usable capacity out of a Prius's tank, at 45 MPG that'd be only about 470 miles of driving range.

IMO, a civil tone should be the responsibility of the user, not of a "dirty words" filter. Obscene language is one thing, but when the filter blocks out common intensifiers used to convey emotion, that's being a little too nanny-ish. I guess I'm... er... "darned" if I do, "darned" if I don't.

 

While I agree that diesel fuel produces more CO2 emissions per unit volume (e.g., gallon), I don’t completely agree that there’s necessarily “additional air pollution” because of the “Bin” to which a specific vehicle line is certified, or at least not significantly more. I’m an atmospheric scientist (hence the “wxman” moniker), and have been involved in the air quality field for nearly 25 years, so I have more than a superficial interest in the subject.

We are really approaching diminishing returns with respect to emissions from new vehicles. For example, most light-duty diesel vehicles are Bin 10, Bin 8, or (soon) Bin 5 because, and only because, of NOx (they’re typically near or below Bin2/SULEV limits with respect to the other regulated pollutants and even Bin 1/ZEV in some cases). However, based on the latest EPA National Emissions Inventory (NEI - 2006), a hypothetical U.S. car fleet consisting of 100% Bin 2/SULEV vehicles emitting at that Bin’s limit for NOx (0.02 g/mile) would reduce the total anthropogenic NOx emission inventory less than one-half of one percent (0.48%) compared to a fleet consisting of 100% Bin 5 vehicles emitting at that Bin’s limit for NOx (0.06 g/mile – approximate average of 0.05 g/mi @ 50K miles and 0.07 g/mi @ 120K miles). As a matter of fact, the reduction from a U.S. fleet of Bin 5 vehicles compared to a fleet of Bin 1/ZEV vehicles would reduce the NOx emission inventory less than 1% (0.72%). So at the very least, there are much larger anthropogenic sources of NOx that need to be addressed than Tier 2 light-duty vehicles, gas or diesel.

Furthermore, the emissions limits for each of the regulated criteria pollutants in Tier 2 are actually quite arbitrary, and don’t really reflect the relative impact on air quality of the respective pollutants. In my opinion, NOx is the least problematic of the regulated pollutants from an air quality perspective. This is why I find many of the “green vehicle guides” (including EPA’s) to be at least somewhat misleading.

 

At temperatures above 65F, I plan and get 500-600+ miles per tank. But then if I run out of gas, I just use the hybrid system to find a safe place to park and add 1 gallon from a spare can and find a gas station within 50-60 miles.

Once upon a time, my brothers told me running out of diesel was bad news. They mentioned something about "bleeding the injectors." Is that still the case?

Bob Wilson

 

Economy minded drivers with the right conditions yes, however once there is very little steady speed conditions like the typical CA metro highways things change quickly.

In our case the economy vehicle gets used fro all the short trips and as a result does about a 1/3 of its miles in trips of 2 or less miles. Stop, shut off the engine go do something and then return later to startup again and go another short distance. Since it is the most economical it only makes sense to do the most trips with it. In addition the "highway" miles has a very large portion of it between 5-30MPH constantly changing in peak hour traffic, the rest is stypically constantly changing between 70-80MPH on a hilly highway. Under these conditions (which is typical for a lot of commuters) it is very hard for a diesel to achieve those excellent mileage figures.

A friend of mine has the new 08 Passat 2.0 TD with DSG and he is pretty easy going on the throttle. He feels very good to get low to mid 30s and has yet to reach the 40s on any trip. He does a normal commute. While these figures are very good they are hardly earth shattering, and confirms when I compare to what I have achieved with various TDs and other folks I know.

While it is still very good it is a long shot from the 60-70MPG some articles have claimed the new TDs will achieve. SImilar to the hype that hybrids had when they first came out.

That is the reason why I like the figures from CR as it shows what the average bloke should expect under different conditions. Most people know if they drive more or less economical than the norm and can adjust the figures accordingly. That way people don't end up with the disappointment that they can't achieve the excellent mileage claimed by others, as often seen on TD and hybrid forums from folks posting. The problem is that most folks posting on the internet about mileage are the ones that try to squeeze the last inch out of a drop of fuel, not the average Joe.

Either way it is a significant improvement over the mid 20s the average sedan on the road achieves today.

A general rule of thumb that has worked very well is to expect 25-50% improvement on fuel mileage of a TD compared to the same gas driven vehicle, 25% (or even less) if you have higher engine loads and up to 50% more if you tend to drive with low engine loads.

Hybrids have been pretty tricky to pin down just yet due to the nature of the technology.

 

Basically you have to purge the air out of the fuel lines. The engine will do that yourself if you just crank the starter. It'll take more cranking than a normal start, of course, but VW/Bosch starters are rated for up to 30 seconds of continuous cranking, so there's no harm being done. I do it every time I change the fuel filter (every 40k miles) and have never had a problem.

On older Mercedes diesels it's even easier, since they give you a hand pump on the engine to let you bleed out the air manually before you crank it. Just give it a few pumps and you're good to go. I ran out of fuel once in my '81 240D and the entire process only took a couple minutes.

There's actually more risk in running out of fuel on a gasser, because the electric fuel pump is cooled by the gasoline it pumps, and once it runs dry, or even if you get too low on the tank, the pump can overheat and that will shorten its service life. (On my gasser '91 Golf, when I got below a gallon left in the tank, the electric fuel pump would start whining, and I could hear it from the driver's seat.) On a diesel, the injection pump does double duty of drawing fuel from the tank and injecting it into the cylinders, and is mechanically driven by the timing belt or chain (no electric power is needed).

 

I'm hardly an expert in this field, but I have noticed that the newer EU emissions regulations have become much tougher on NOx. So I have to guess the folks at CARB and the EPA actualy have a clue what they are doing.

I found this reference very handy for having a basic understanding of different types of emissions and how they affect air pollution.
http://www.vcacarfueldata.org.uk/inf...-pollution.asp

So I looked at the EPA applications for the 2006 Jetta 1.9 TDi, 2007 Camry 2.4L and Camry Hybrid. No listing for the "clean" diesels that I could find at this time.
http://www.epa.gov/dis/


The main ones listed were CO, HC-NM+NOX-COM (guess refers to hydrocarbons) and lastly NOX. They also list NMOG, but I have no idea what that means. Lastly they list PM for the diesel but not the gassers. CO2 or greenhouse gas is directly related to the listed mileage, obviously a premium of about 15% needs to be added to diesel due to it's higher carbon or energy content per volume. Also keep in mind that CO2 is not considered an air pollutant nor toxic for humans, rather related to the debate on global warming.

TDi results were:
CO - 0.03
HC-NM+NOX-COM - 0.7483
NMOG - 0.0141
NOX - 0.31
PM - 0.046

4Cyl Camry
CO - 0.21
HC-NM+NOX-COM - 0.077
NMOG - 0.0198
NOX - 0.016
PM - NA

Camry Hybrid
CO - 0.03
HC-NM+NOX-COM - 0.008
NMOG - 0.004
NOX - 0.001
PM - N/A

So the diesel does well on CO, but is substantially higher on HC (10x vs Camry and 100x vs CamHy) and NOx (20x vs Camry and 310x vs CamHy). Needless to say I think CamHy is what manufacturers should be aiming at (T2B3).

T2B5 (minimum diesels seem to be aiming at and most gassers) is not that great, but still will cut the TDi as listed above with 12% for HC and 77% which is substantial in my book.
CO - 4.2
HC-NM+NOX-COM - 0.65
NMOG - 0.09
NOX - 0.07
PM - ????

T2B3 (where we probably should be)
CO - 2.1
HC-NM+NOX-COM - 0.62
NMOG - 0.055
NOX - 0.03
PM - ????

I would love to see the results of the new "clean" diesels as I find the improvement in air pollution from the Camry to CamHy very remarkable. This is something a lot of people overlook when they talk about hybrids, most "good" hybrids have a remarkable improvement for air pollution vs their non hybrid counterparts (much more than the fuel economy improvement it seems).

 

This was back in the 70s when my brothers told be about it. My Dad had bought an old Mercedes and I was home on leave. That feature must have been it.

Having run out of gas over two dozen times in my gasoline studies last year, it doesn't happen quickly. So far, not even a peep but then this might be specific to each design.

Bob Wilson