Colder weather has zapped my mileage to 44mpg

If the MPG drop in TDIs is not quite as intense as it is in the Prius (and you agree) and TDIs appear to run above EPA even in the winter, how come their year-round average does not keep up? Maybe I did not get the idea?

As long as I keep my Prius, I will be glad to show my data and discuss what I can do to try to minimize the MPG drop...

Thanks for allowing me to post here mister Priuschat owner...

 

The year-round average for TDI's does not seem to keep up with the year-round average for a Prius (assuming you live below the Arctic Circle).

 

I see now... I misunderstood you. OK, I agree...

 

He doesn't say anything about the accuracy.

Ken@Japan

 

LOL.

There aren't many vehicles with a 'coefficient of drag' as low as the Prius. <grins> What tends to happen is as the coefficient of drag goes lower, the rolling drag effects remain predominate at higher speeds.

You are dead on about the '<less efficient> at a broader range of speeds.' I wouldn't call another vehicle 'wasteful' since we don't know the full mission profile. Certainly a D-4 Caterpillar is not an ideal commuting vehicle unless you have to commute through a pile of dirt and debris ... like a traffic jammed highway. I've long suspected the attraction of "Big Wheel" vehicles are 101 day dreams spawned while sitting stationary in an expressway traffic jam. <grins>

For some folks, having a consistent cost of operation, even if over the long run the costs are somewhat higher. It means they don't have to run a deficit in some seasons for an advance in others. It has nothing to do with overall efficiency but a simple question of budgets, planning and expectations.

Bob Wilson

 

Interesting posts. But without using any scientific control group, or driving any specific or particular way other than hopping in the vehicle and going, paying no attention to any of these: road, speed, weather conditions, tire pressure variations, or any other factors which may affect overall mileage, in the past 3 years, I noticed that both the Prius I drive ('07) and the one my wife drives ('08) do better in the overall fuel economy stats when the outside temps are 65-75 degrees. Hotter temps reduce efficiency as do the colder temps. I know all the reasons that could be causing it, and at this point, I don't really care. I know how "the beast" works, and if I could change the climate to stay between those temps night & day for 365 days a year, the cars would love it!!!!

 

Accuracy between MID and calculated? Pretty close according to a single report I got.

Look, it is too early for any conclusions about the A3 TDI FE, so all I got so far are a few reports from isolated super-happy onwers who have had their cars for a few days. It does appear that their cars are keeping up pretty well with EPA despite of winter.

However, there is plenty of evidence elsewhere that TDI engines in general suffer from a minor MPG drop during winters...

 

But I'm not sure what else I could do? I have blocked the lower grille, I keep the cabin colder than I wanted, I over-inflated my tires, I drive at average speeds of 66-67 MPH in the hwy... I mean… what else for heavens sake?

Block the upper grille? I don’t think so... that's too risky. I have the scangauge but what if the inverter overheats before the water temperature? Then I'm toasted.

Drive slower in my trips? Come on... I drive at night for almost 6 hours... Last thing I want to do is to drive for 9 hours in the middle of the night at the expense of some good FE. Then it would become really unsafe driving beyond midnight and my back would suffer like a working horse from the lousy seats. Enough with that!

I just have to cope...

 

You already have the most efficient vehicle at the speed you drive (at any price or size).

Aerodynamic improvements should help you. Put back the rim rings back on, that should help. Reducing the air flow prior to reaching the front of the car will help too. Don't lead the pack, let someone else do it and you follow.

 

To look at TDI performance, you might consider going to:

Browse All Volkswagen Jettas | Fuelly

The Jetta TDI, sedans have a normal distribution curve and you can get individual records such as:

2010 Jetta (VW Jetta) | Fuelly

Now a couple of years ago, some Jetta folks felt they were getting an unfair, EPA rating and I produced this chart using Fuel Economy data:

Now NHW20 Prius owners in the lower quadrant of Prius mileage, 45 MPG or lower, pretty much overlap the Jetta TDI range. For them, a Jetta TDI would be no big change in mileage result ... they are already there. The risk is that instead of mapping horizontally over the Jetta TDI range, they may map vertically, into the lower quadrant of the Jetta TDI range:

37-45 MPG (Prius) -> 32-39 MPG (Jetta)
​

But it really comes down to their expectations and vehicle requirements. All we can do is dispassionately look at the data and share the observations. Someone has to 'do the experiment.'

Purely idle speculation but IK's ideal vehicle mix might be:

• TDI diesel - cold weather, highway driving
• Prius - all other conditions, urban and temperate driving

Bob Wilson

 

Date 1-15-2010, time 11:30PM EST, route from junction of I-80/94 and I-65 to junction of I-65 and I-865, temp 27F, lower grill blocked, tires well inflated, climate control on defrost at 70F and 1 bar on fan speed.

51.2 MPG indicated-46 MPG actual, average speed 64 MPH

Date 1-17-10, time 2:30PM EST, reverse of route above, temp 31F, everything else same.

51.3 MPG indicated-46 MPG actual, average speed 67 MPH

That particular stretch is a killer because of the crosswinds.

Wayne

 

Bob,
Indy & I have the same problem, in a way: He needs the Prius and a TDI, but cannot afford two good ones, so he'll likely wind up with a TDI only (or keep the Prius, either way sub optimal for his needs).

I mostly need an EV with very modest range and top speed, but must have a car for long trips, too. Rental would be too frequent. I cannot garage both vehicles or afford to carry them, so I have a Prius. A PHEV Prius with no more range than the current GenIII test PHVs (or even the GenII test PHVs) would get pretty close to ideal for me.

 

I mean "wasteful" in the sense that they could be more efficient for their intended purpose, but aren't. (styling considerations and whatnot take some priority - true of any car including the Prius, but moreso in some than others. Even the Fusion could be more efficient - 20% more weight for a marginal increase in cabin volume, no real explanation why)

A Catapillar tractor capable of doing burnouts would also fit my definition of "wasteful", unless its "mission profile" is for entertaining thousands of spectators. (Truckzilla isn't necessarily wasteful because the amount of fuel spent per spectator is probably quite small, unless you believe spending any fuel for entertainment is a waste - which would basically kill any/all forms of entertainment...)

But to get back on-topic, if your mission profile is a high-mileage car for winter-only highway-only driving, the Prius probably loses compared to high-efficiency diesels. Year-round mixed driving is a completely different story.

Some people do have multiple vehicles, one of which is predominantly for a certain type of use (like snow or highway or off-road), while a different vehicle would be used for driving which is substantially different (around-town, short trips, etc).

So while the Prius is the "best all-around", if you're in a niche like highway-only/winter-only, it may be outclassed by the best in that particular category. You just have to decide if your driving is far enough into the niche to justify using the best-in-category, or if your overall patterns are better server by the "best overall".

"Best overall" is not the same as "one size fits all".

 

This is kind of like snow tires vs all-season - all-seasons are better most of the year, but snow tires are way way better in the white stuff. (of course, it's a lot cheaper to get a 2nd set of tires than a 2nd vehicle...)

 

Indy> Have you looked at fuelly, or fueleconomy.gov? So far, the A3 only has a single entry in both, however both are below the EPA rated highway by 2-3 MPG. Isn't this one of your criteria? The Jetta seems to be at, or slightly above it's highway rating on fueleconomy.gov, but it's harder to tell on fuelly. However, it seems lower on the vehicles I glanced at.

In comparison, all model year Prius starting at 2004 beat the (albeit updated) EPA estimate by 1-5 MPG for highway on fueleconomy.gov. I did not search fuelly for the Prius.

So, if you're one of your major sticking points is beating the highway EPA, on a yearly average, the Prius wins over the TDIs based on averages found on a fairly well documented site.

Something else... the elusive math that if you slow down by 7 MPH that it will take an additional 3 hours to reach a destination. Have you actually done the math? It would not appear so on this end.

You've mentioned trips of 329 miles. If (assuming they were all highway) you averaged 67 MPH on those trips, it's just a tick under 5 hours to complete... it's like 4 hours 54 minutes. Now, let's say you slow that average down to 60 MPH. Total trip time is just shy of 5 hours 30 minutes. To me, gaining 5-10 MPG for an additional 30 minutes is very much worth it. For others (my father being included), not so much.

This whole "it takes for eva if I go slowa!" stuff is bunk. So, are you truly averaging 67 MPH? Or is it closer to 72 or 75? At 75 MPH, that trip would take 3 hours and 22 minutes. We're now at a 2 hour differential, but still not 3.

 

I have a 2003 Jetta Station Wagon TDI 5-speed manual tranny.

I can tell you that in 130,000 miles of driving the TDI, my car MPG
does not take a big hit in Winter and it is always, I mean always, over the 2008 EPA. Even over the 2003 EPA.

The Prius MPG is noticable lower by a high degree than the EPA in the winter on a regular basis, as the large percentage of the owners seem to be reporting.

Alfon

 

Good.

Now what is your average MPG in the winter with:
- Jetta Station Wagon TDI 5-speed manual; and
- Prius 2010;
on identical use patterns (short/long trips, speed, etc).

 

So the TDI and Prius are nearly the same actual (calc) MPG in winter, with the Prius being substantially higher in warmer months - correct?

 

It could well be, but in my situation, the case for "better FE in the summer compensates the winter drop" just does not fly because of my HWY-only and substantial driving. Where I drive, looking at the average temperature charts, my lifetime MPG won't start going back up until mid-April, which is when I will have about 25K miles in my Prius... With that much miles on it, it would have to take substantial increases in my trip MPG after mid-April to cause any a considerable impact on my lifetime MPG... then on mid-October it will start plunging again.

I think those with much shorter commutes and less HWY driving could still get decent lifetime MPG in their Prius even in areas with miserable winters... but it is not my case.

 

Wayne, the calculated MPG in this case was 10.15% bellow indicated (MID)!!!!

I'm so glad to see that. That is ridiculous! My Prius does that for every 5-6 hwy trips and I thought there was something really wrong with my MPG gauge.

The discrepancies (calculated always bellow indicated) can vary anything from 3.7 to 10.6% with average of 6.56% in my trips. The discrepancy on MPG send to the scangauge is even worse, in other words, even more overestimated!


There is something odd about the metrics algorithms in the Prius that makes it so inconsistent and wrong. I’m glad I use GPS-verified speed for my data because the MPH sometimes goes way off too.