Colder weather has zapped my mileage to 44mpg

I think the sum total of what we have learned here is:

1) The Prius takes a significant (10-20%) mpg hit when temps go below freezing.
2) This hit is more dramatic (15-30%) for high-speed driving (>65mph).
3) Both of the above seem to disappear in temps >45F

4) We still haven't figured out why... And I think many of the possibilities mentioned would show linear differences in changing temps, rather than exponential.

Grill blocking didn't help me much in this context, but without a Scanguage I am only doing about 85% lower and 45% upper. Has anyone tried 100%/100% on a highway trip in temps below 30F? I would be interested to see if that made any significant difference.

And does anyone have any technical data about rolling resistance (tires, mainly) in colder temps? My suspicions lie in that direction...

 

You're in the driver seat so Good, Fast, Cheap, pick two of three. BTW, I was just over at Consumer Reports and the Ford Fusion hybrid has pretty high owner satisfaction.

Just for grins, you might try a test drive in a regular Fusion and scan some of the Ford hybrid user sites. A USA hybrid might be better designed for our style of highway driving. I saw the engine and transmission setup at the Detroit Auto Show and it looks to be a good system. ... Just a thought.

Also, you might open the search to include Ebay (no experience with Craigslist.) If you find the car you want at a dealer, give them a call. Having a wider search area you are better equipped to strike a deal that works for you.

One last thought, post a description of your 2010 in the For Sale area with a pointer to the dealer who got it. We see folks come here from time to time looking for a good deal on a Prius and a used one, freshly traded-in might be just the thing.

GOOD LUCK!
Bob Wilson

 

Yea, from those numbers it looks like nothing is wrong with your car. I assume you still have the grills blocked when you performed those tests.

Air resistance is not constant as your speed increases. If you double the speed, the air resistance increases 4x.

I am interested in how TDIs perform in high speed (75mph) in extreme winter temps. Did you run across any numbers from TDI owners?

 

I've found these:


And:


Roughly it looks like a 4-5 MPG hit going from a 2010 Prius to Jetta TDI but mileage isn't the only requirement one might have.

Bob Wilson

 

Good points.... Attached is the table for my MPG hit history after 28 long trips...

 

Sorry, but "lifetime mpg 46.8 - ouch!" :lol: Oh, the tragedy and oh, the drama! :Cry:

EPA highway is 48 so you're within 2.5% even though most of your miles have been in colder temps (at speeds higher than the EPA test regimen). Buck up, sonny.

My "lifetime" mpg is 42.8 - but I started in late-December (during one of the coldest late Decembers on record). I'm not going to get all weepy unless I see the same numbers come May - and considering my displayed mpg jumped all the way to 52 on the first warm day (with snow tires), I'm not too worried.

 

That said, I'd like to find the real cause of lower mpg in cold temps to see if it can be mitigated somehow (even if only partially).

 

Some factors yes, some no. Even with the linear factors, there are multiple factors. Summing these can produce dramatic and unexpected results, especially when you focus on only one or two, but all are really in the equation.

Just a suggestion, but I have found that you can force a Prius to have consistent summer and winter performance, or at least make it behave like a conventional car. In warmer weather depress the parking brake until it is half on. The downside is that the rear brakes wear out pretty fast, but then that is also consistent with normal cars.

Tom

 

Thanks for the tips Bob. I'm picking Good and Cheap... I'm not in a hurry...

I think the Fusion hybrid is a better choice than the A3 as far as reliability, I agree, but the problem of the fusion is low MPG estimates for hwy (only 34 MPG I think) and I need a hatch to fit all the bulky staff I transport.

Also, I really miss driving German cars… an important part of it is about how the car makes you feel. German cars are often more passionate than the Japanese. I like them because of their attention to their design and details in a way that Japanese cars don't quite. My bother and many of my friends loves Audis and other German cars despite of the much lower reliability ratings… they don’t care and I’m finally coming to understand them better…

I'm checking the winter MPG hit from real 2010 A3 users (I found just a few online) and it appears that it is much less dramatic than the Prius...

 

The reason for the drama, once again and for 2 million times, is that keeping my lifetime numbers at least 3-5 MPG above EPA estimates has never been an issue of any of my past cars without any minimal effort to be more FE whether if it was winter or summer…

My Prius lifetime is at - 3 bellow EPA right now but going down as I drive and will bottom 40 until winter is over. Will it rebound to EPA levels before next winter? Probably not...

So, I never got that kind of drama and problem even from my first and last dodge gas guzzler…

 

I don't quite agree:

My feeling is everyone should make their own decisions and live with the consequences and I would like to see his 2010 Prius find a new home. IK certainly has a right to 'do the experiment.'

If nothing else, IK has found PriusChat has a lot of technically skilled folks. Look at this thread and apply a standard $50/hr., close to $10k dollars of expertise and over 50 man-years of Prius expertise have looked at his 2010's performance. I'm pretty sure the consensus is his 2010 Prius is behaving as expected.

In engineering we have a concept called, "managing user expectations." Sometimes a solution is rejected because the user had different expectations. This highlights the problem with the current EPA rating system ... it has no provisions for speed and weather conditions. IK's experience shows how this can 'go wrong.'

When I could not find mph vs MPG charts or weather correction charts, I made my own. So now I can predict mileage, which gives our family an edge in trip planning. But this discipline came from flying. Every plane comes with charts used for takeoff distance, cruise, and climb performance ... the living pilots make these charts part of their standard practice.

Bob Wilson

 

Yes, but many of us wish he would whine less in the process. It makes it seem like he's more interested in sympathy than answers.

We have the same concept - and sometimes a solution is rejected because the customer's expectations are unrealistic.

The EPA tests now include "hot" and "cold" testing, and also a peak speed of 80mph - which is a step in the right direction even if it doesn't fit your definition of "real-world" driving. They also "fudge" the numbers a bit lower to offset unrealistic expectations. The fact is, the EPA pattern isn't "real-world" for anyone unless you happen to drive the exact same patterns in the exact same way in the exact same temps and other conditions - but it is a pretty good ballpark figure (that's why they call it an "estimate") which is likely to be within a few % for average drivers in average conditions. And it serves as a relative comparison to other vehicles - good luck getting 48mpg highway with a Fusion.

IK's unrealistic expectations are that he expects better-than-EPA mileage even under adverse conditions, all while doing a type of driving which is more strenuous than the EPA pattern.

[emphasis added]

Despite this, IK's is unshakeable in his belief that his mileage is "terrible" and won't average out in the warmer months.
IK: 1, experts: 0

 

I would like to know exactly what in particular is causing the non-linearity of the mileage decline, rather than write it off as "the sum of many small factors which interact in unexpected and inexplicable ways". (sounds too much like "Engineering is more art than science", which all engineers know is just B.S. to get the non-engineering types off your back)

To get back on-topic, the facts are:
1) almost all Prius owners see a mileage reduction below freezing temps, under all conditions.
2) this reduction is more dramatic (i.e.: non-linear) compared to equal (or greater) temperature changes above freezing.
3) this reduction is more dramatic (again, non-linear) at highway speeds.

I did 75% grill blocking and saw no change (unless the degradation is even more non-linear than supposed).

 

I am not Tom, I swear. I admit it... I can be a pain in the neck when I want to and I have been more than I should, but look at my later posts here. All I'm trying to do is post real honest data about my Prius FE. The only time I'm whining is in response to people trying to pick up a fight. I thought my table with my MPG drop numbers were interesting but instead of a “tank note” or a “cool comment about it” I got someone complaining about the "ouch" part. What can I do if the “ouch is really my honest feeling? Like I said before, I always drove the same speeds in the hwy and went through the same winters, and yet keeping up with EPA estimates in all my past cars was a breeze compared to what I have to do with my Prius.

 

Of note, grille blocking does not appear to be helping with 100% HWY driving in my case but I would like to collect more trips with the blocked grille to draw a more confortable conclusion...

 

Ok, ok - "I feel your pain". Or I might if I was doing 2000 miles a month all highway and saw mpg which was only 83.3% of EPA and was expecting overall mpg of 105% of EPA and expected that year-round. (which I guess is another way of saying I don't really feel your pain...)

But if you want answers, stick to the facts - and I agree with you on the facts: the Prius has a significant, non-linear drop in mileage in below-freezing temps at highway speeds. And I would like to know why.

Items explored so far:
1) Grill blocking - partial blocking seems to have little to no effect. Has anyone tried 100% upper and lower to see if that changes anything? (I would be willing to try myself if I had Scanguage) If we get "overshoot" on this (engine overheating), that completely debunks blocking for highway driving (although it's definitely better for cabin heat on shorter trips).
2) Aerodynamics - plenty of good data here, but the graphs look pretty linear. So yes this is a cause which ties in with cold temps especially at highway speeds, but no, it doesn't appear to be the non-linear element.
3) mechanical inefficiencies related to cooler fluids and whatnot - seems unconvincing for long trips where most/all of the fluids would reach normal operating temps within the first 2-3% of the trip.

Items not yet explored:
1) HV battery temps - could be a parasitic loss when the cabin is cold or the HV coolant is below freezing? 100% upper block might provide some insight into this, but this may be a hard one to pin down conclusively.
2) tire rolling resistance - could be a significant loss point at highway speeds if the tires never warm up to a point where they roll efficiently. This will be a b*tch to figure out since it has more to do with materials science and will be difficult to get conclusive numbers. If anyone has any data about this, I'd love to see it.
3) other suggestions?

 

Bob,

I've found your engineering contributions, along with the contribution of others, to be very beneficial. Thank you for taking the time to offer the free engineering consulting advice/data.

 

Sounds to me like you have a project. As it is, I don't think you have enough real data to even state that the decline is non-linear.

Tom

 

I won't even give you the time of day for $50/hr. You're giving away my services for cheap.

Tom

 

By the way, if anyone is curious, I've found that the mileage drop on my 2002 Jetta TDI to be relatively small in the winter (from about 48 mpg in summer to about 46 mpg in winter)

The following is my mileage graphic from "Your MPG" on fueleconomy.gov. I began to contribute to the site in May of 2006 and it goes through December 2009...