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Temperature vs mpg

Discussion in 'Gen 2 Prius Fuel Economy' started by duanelaugh, Aug 28, 2006.

  1. duanelaugh

    duanelaugh New Member

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    After several tests at different temperatures, my '06 Prius, 1500 miles, gets 46 mpg at average temps of 95 degrees plus. However, at 75 degrees that jumps to 56 mpg. This is over a course of 40 miles, ACset at 79 degrees. Approx 50 percent on the interstate, 25 percent on rural highways and 25 percent on city streets. In my experience each 10 degrees over 75, it costs about 4 or 5 mpg. This seems more significant than even tire pressure, which I have set at 38 front and 36 psi in the rear tires.

    Just for info, Duane
     
    #1 duanelaugh, Aug 28, 2006
  2. berylrb

    berylrb Member

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    <div class='quotetop'>QUOTE(Duane @ Aug 28 2006, 10:00 AM) [snapback]310530[/snapback]</div>
    Hey Duane, welcome to PC if you havent' been already. Hey, question for ya, could this possibly be more about AC then temp? That is, if you have the AC set to 79 it wouldn't come on for your 75 degree test, whereas it would be running alot with your 95 degree parameter, eh?

    Search for AC threads and I think they were talking about the same numbers 4-5 mpg running AC or not.
     
    #2 berylrb, Aug 28, 2006
  3. efusco

    efusco Moderator Emeritus
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    Unfortunately your numbers are a bit difficult to use due to the AC use and the variability of terrain and such.

    But yes, the temps are an important factor. If you run without AC your mileage will get better as temps get higher, but the cost of running the AC tends to balance things a bit.
     
    #3 efusco, Aug 28, 2006
  4. richard schumacher

    richard schumacher shortbus driver

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    <div class='quotetop'>QUOTE(efusco @ Aug 28 2006, 10:11 AM) [snapback]310538[/snapback]</div>
    Up to the point that the traction battery gets too hot. If the driver can hear the battery vent fan then the battery is too warm.
     
    #4 richard schumacher, Aug 28, 2006
  5. duanelaugh

    duanelaugh New Member

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    [Yes, that was my thought exactly....the AC was the additional load, maybe not so much the air temp and engine. The area I was driving was perfectly flat with only slight hills over the over passes. All the tests were over exactly the same roads. The outside air temp has been in the mid to high 90's here in the Sarasota area ever since I picked up my Prius with only ond day that it dropped to 75 degrees. The temps are from the outside air temp reading on the highway.
     
    #5 duanelaugh, Aug 28, 2006
  6. eagle33199

    eagle33199 Platinum Member

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    Also, please realize that this is a rather limited sampling, the results of which rally don't tell us much. With only 1500 miles on the car, you're still breaking it in, which means the car itself is slowly being able to get better mileage (as mechanical parts wear off the rough edges), and your driving skills for getting good MPG are slowly improving (since 99.9% of people didn't have any way of seeing realtime MPG data before owning a Prius). Additionally, there are other factors that could effect the MPG which weren't listed as being the same, such as wind conditions (tail wind versus head wind). Additionally, with only having one day that dropped down to 75, you don't have much of a basis... there could be any number of reasons to get better mileage on that one day that have nothing to do with temperature.

    That being said, you can be sure that having the A/C on does drop your mileage by some degree, especially with temperatures over 90.

    Unfortunately, in order to acurately test a hypothesis like the one you proposed, you'd need to get a climate controlled room (like the one the EPA uses for their mileage tests) and create identical conditions for the car (including acceleration and deceleration), with the only exception being the temperature and A/C usage... Baring that, i'd say give it a year or so to accumulate sufficient mileage data over time, then come back and see if those averaged results support the hypothesis. You might have to account for other linear trends in the data, like the break in period, in order to equalize everything.

    All in all, it's a good start, and at least you have a working hypothesis to start from.
     
    #6 eagle33199, Aug 28, 2006
  7. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    I have tracked my mileage for the last two years along with temperature. I have found that mileage per tank tracks the temperature rather predictably. Minor fluctuations are due to various thing - such as the 11-day tank driven through 9 days of rain resulting in an MPG decrease counter to the temperature increase.

    Refer to the chart below. Temperature shades red to blue, the dotted line represents tank averages, and the thick pink line is lifetime average.
     

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    #7 TonyPSchaefer, Aug 28, 2006
  8. berylrb

    berylrb Member

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    <div class='quotetop'>QUOTE(TonyPSchaefer @ Aug 28 2006, 11:57 AM) [snapback]310592[/snapback]</div>
    nice graph Tony, is this detecting global warming too! LOL

    so comment on AC use and your graph if you please?
     
    #8 berylrb, Aug 29, 2006
  9. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    <div class='quotetop'>QUOTE(berylrb @ Aug 28 2006, 11:13 PM) [snapback]310967[/snapback]</div>
    What I point out to new drivers is the first ten months of learning curve before I posted any good numbers.

    As for A/C, I use it sparingly don't shy away from it. I carpool now and my passenger pretty much insists that it be on. Of course, when it's above about 80ºF outside it's coming on anyway, but usually only enough to take the edge off the heat. Also, on a trip-bt-trip basis, I don't see a substantial MPG drop that I can attribute solely to A/C when I'm maintaining movement. The only time I can blame A/C is when I'm standing still and the A/C is pulling down the battery. But even with the A/C running, if you try to adhere to proper PnG techniques, coast when possible, stealth when possible, anticipate stops and all that other stuff, it's all good.

    For the full list of tank-by-tank comments, click the link in my signature. You understand that I'm not going to recreate it all here.
     
    #9 TonyPSchaefer, Aug 29, 2006
  10. NorwoodIV

    NorwoodIV New Member

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    11-day tank driven through 9 days of rain resulting in an MPG decrease counter to the temperature increase.

    Refer to the chart below. Temperature shades red to blue, the dotted line represents tank averages, and the thick pink line is lifetime average.
    [/quote]

    Now, we need you to adjust the chart to include humidity, barometric pressure, and approximate altitude above sea level. How many passengers did you carry each time? Was the car clean? Do you have a dog? How much do you weigh? Do you tend to eat heavy meals? Did the dog eat a large meal?

    You clearly are leaving way too many loose variables in your data collection and reporting. The conclusions you draw and report simply don't give the readers nearly enough information and may be misleading. :D

    (All kidding aside, a very interesting thread...)
     
    #10 NorwoodIV, Aug 29, 2006
  11. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    Oh man you really had me going there for a minute. I know that there are those who would want to add those columns and track it all on a day-by-day basis recording the "actual temerature while driving" as well as the other variables you mention in addition to ones we'll probably never think of (you all know who you are).

    I am certain to make it clear that my stats are for guestimating and making wild accusations. They are not for scientific analysis.
     
    #11 TonyPSchaefer, Aug 29, 2006
  12. NorwoodIV

    NorwoodIV New Member

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    <div class='quotetop'>QUOTE(TonyPSchaefer @ Aug 29 2006, 03:42 PM) [snapback]311273[/snapback]</div>
    Heh heh, good disclaimer. :D

    Seriously though, have you seen any data to correlate passenger/cargo weight to loss of MPG?

    It would be tough to have a controlled test, but I would be curious to know what an extra person costs. 5%? 10%?

    Knowing would make it easier to garner my fair share of Starbucks credit when carpooling.
     
    #12 NorwoodIV, Aug 29, 2006
  13. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    Personally, the cost of a passenger is psychological. When alone, I don't mind putting on some tunes and holding up traffic at my own pace. Okay, I tend to try and keep up with traffic for the most part, but when I have my carpooler, I feel compelled to go just a little faster or drive with a heavier foot if only so she doesn't feel that I'm driving too slowly. When I'm by myself, not so much. Also, when I have a passenger, we get talking and I keep less attention on the mileage reading which leads to a heavier foot and a lower overall average.

    When it comes to carpooling, I'm the sole driver. Trust me, it's better for everyone this way. :) I get 15 dollars for every 12 carpooling days. Since we don't carpool every day, we only count the days when we do. I'm averaging 49 MPG lifetime, averaging 10gal. per fillup. With a 40 mile round trip, I go through a tank of gas roughly every 12 trips. Fillups are roughly $30 so she gives me $15 per 12 trips. And that's almost enough for two Starbucks!!

    I haven't seen any hard facts on passenger weight (or cargo weight) affecting mileage.
     
    #13 TonyPSchaefer, Aug 30, 2006
  14. enerjazz

    enerjazz Energy+Jazz=EnerJazz

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    I've now updated my mileage chart to include avg outdoor temperature and updated the mileage vs. temperature graph to include 27 months of data. See it on my web site

    [​IMG]
     
    #14 enerjazz, Nov 4, 2006
  15. Chuck.

    Chuck. Former Honda Enzyte Driver

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    Since it's getting colder, I've noticed that going lite on the heater might improve fuel economy just like going lite on the A/C when it's hot.

    Specifically, ScanGage revealed how going the first few miles with the heater on really delays getting to normal operating temperature....
     
    #15 Chuck., Nov 4, 2006
  16. Frank Hudon

    Frank Hudon Senior Member

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    last week we had several days of freezing morning temps and it took at least an additional 7 blocks to get the car into S4. My trip to work is approx. 20 Km's and when I got to work I checked the battery temp and it was only 11C, and after work with the OAT at 11 C the battery was at 11C and the car went into S4 at approx the same spot it normally does. So getting the battery from 0C to 11 was the killer on the mileage for that trip.
     
    #16 Frank Hudon, Nov 5, 2006
  17. pinball

    pinball New Member

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    Since the snowflake appeared a few days ago my consumption has dropped by 4mpUKg
     
    #17 pinball, Nov 5, 2006
  18. huskers

    huskers Senior Member

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    Damn snowflack!!! :blink:
     
    #18 huskers, Nov 5, 2006
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