Wow - ambient external temperature REALLY matters for MPG

Discussion in 'Gen 4 Prius Fuel Economy' started by galownia, Apr 18, 2016.

  1. galownia

    galownia Previous master neon mechanic

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    Yes, still achieving ~72-74mpg+ both ways to work almost every day. Round trip of ~60 miles with average speed in the 35mph to 40mph. Longer highway trips at 80mph drop me back down to around 60mpg.

    My odo is about 3% high, so the 72 is closer to just under 70mpg actual.

    Jonathan
     
  2. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    Are you sure about that??
     
  3. Mr.MPG

    Mr.MPG Junior Member

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    Southern California Temp has been rising the past week from 70-85, so does my MPG, I average was around 77.5MPG since March, now past few days has been 79.3 to 79.5MPG. Ambient temp does have an impact on the MPG for sure. Silver 2016 Four Touring.
    upload_2016-6-23_13-14-17.png
     
  4. Coast Cruiser

    Coast Cruiser Senior Member

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    Up to near 90 degrees in the next 4 days. What is Winter???! :LOL:




     
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  5. raspy

    raspy Senior Member

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    It's suddenly become very cold in London, with daytime temps down to 41F/5C.

    It's now drinking fuel compared to the summer months, especially for shorter trips (<3 miles) from cold.
     
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  6. Coast Cruiser

    Coast Cruiser Senior Member

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    Thanks for the report, Raspy. I very curious to see how my car performs in colder weather.
     
  7. raspy

    raspy Senior Member

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    It hit me yesterday, as after a 1.8 mile drive with a cold engine, when I switched the car off, the MFD reported fuel economy of 32.8mpg (which works out as 27.3 US mpg)
     
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  8. Coast Cruiser

    Coast Cruiser Senior Member

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    ...My odo is about 3% high...

    When I did my last fill-up, my hand calculated mpg was only 9/10 lower than the computer displayed mpg.
    (No, I'm not making that up. :LOL: I don't "fudge numbers" like some Fuelly guys do.)

    And if I had pulled the nozzle out at the first click-off, my calculated mpg would have been better than what the display said. But I always squeeze in an extra gallon of gas. So I don't understand all the negative comments that the computer display is getting. That has not been my experience.

    The biggest difference I ever had between the displayed, and hand calculated, was only 2 mpg. And that was only on the very first tank of gas when the car was new. Since then, I don't see any significant difference. I'll bet you a large pizza! :D
     
  9. Coast Cruiser

    Coast Cruiser Senior Member

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    Yes, other people have reported similar results. But I think those very short trips are misleading? If you had driven 10 miles, the mpg would probably be normal. Are you looking at the "From-the-Flag" mpg indicator?
    I find that one to be the most misleading.

    I only look at my "Trip-A" indicator. And it's always stuck on 62 mpg.
     
  10. Coast Cruiser

    Coast Cruiser Senior Member

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    image.jpg


    I went to get petrol. Than back home. And this is my MPG. :ROFLMAO:
     
  11. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    @Coast Cruiser I think we're just misunderstanding each other: "odo", short for odometer, is the car's total miles (or km) travelled since built. Nothing to do with mpg.

    And yeah, from reports here, the 4th gen's mpg display appears to be more accurate. 3'rd gen is 7.5% optimistic in my experience. 4th gen is 3~5%?
     
  12. GT4Prius

    GT4Prius Active Member

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    Am I stating the obvious in saying that Prii use more fuel in cold weather in keeping the cabin warm. I leave the heater turned OFF for very short winter journeys and as a result get FAR better mpg than with the heater on. This is with a Gen2.

    I guess that the mpg hit will vary according to use of eco mode or not and requested cabin temp, and the hit is prob less in more recent gens but the car is still likely to run the ICE more in cold weather in order to heat the cabin isn't it, especially when stationary?

    Posted via the PriusChat mobile app.
     
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  13. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    The car's computer monitors ambient temperatures, and (I strongly suspect) changes warm-up protocol as temperatures drop, running the engine more and longer. And I know for sure the cabin temp you set makes a difference: I've been sitting at red light with partially warmed car and can consistently turn the engine on/off by just raising/lowering the cabin temp. The threshold is somewhere around 21.5C (70F).

    Our's is third gen, but I'd think this is applicable to other gen's too.
     
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  14. Coast Cruiser

    Coast Cruiser Senior Member

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    Yeah, I meant the MPG display... not the ODO.

    And as everyone knows by now, I only check my MPG after I've gone thru a full tank. I'm old school. The only thing I look at is the little Trip-A window. (If the day ever comes, when I start checking my MPG after driving only 2 miles... throw me in the Funny Farm!! :ROFLMAO:)

    And when it's cold, I want some heat! And when it's HOT (90 today) I'm going to blast the AC. I'm not going to squabble over a little tiny loss in MPG. I wouldn't care if the miles per gallon dropped down to 50! I'm still good with that! Where else am I going to get 50 MPG????? (And have a nice COOL car. :))

    For corn's sake! I'm not going to pinch pennies just because I'm driving a Prius.
    And I got another gripe... Where is that headlight thread… I can't believe all the Pre-Eyes I saw that didn't have their headlights on in a heavy fog!!!! Are they trying to save five cents or something!? Heaven help us.

     
  15. raspy

    raspy Senior Member

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    I was looking at one of the two small screens in the centre that always reports mpg for the current journey a few seconds after you switch the engine off.

    Posted via the PriusChat mobile app.
     
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  16. Tideland Prius

    Tideland Prius Moderator of the North
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    Yup. Judicious use of the ECO Heat/Cool function and setting a lower/cooler temperature can help reduce the impact of cold weather.

    Of course, you could turn off the climate control (assuming your windows won't fog up) and use the seat heaters instead.

    I usually set my temps to 21°C or 21.5°C in ECO mode in my Gen 3 to reduce idle time. (ECO mode in the Gen 3 has a lower water temperature threshold for engine shut off compared to normal mode so the engine will shut off sooner)
     
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  17. GT4Prius

    GT4Prius Active Member

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    Your decision if you want heat over mpg, of course. But on what evidence do you say that turning off the heater would be a "little tiny" improvement? IMHO the degree of difference depends on the length of the journey as well as outside temp and inside temp setting, so the difference will vary greatly for different drivers at different times. For us the difference is not tiny, it's very marked.

    Posted via the PriusChat mobile app.
     
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  18. Prodigyplace

    Prodigyplace Senior Member

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    On my 2017 I have found that the fan speed of the climate control makes a big difference in MPG. The Eco mode does not appear to adjust the speed automatically.
     
    #58 Prodigyplace, Nov 9, 2016
    Last edited: Nov 9, 2016
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  19. 70AARCUDA

    70AARCUDA Active Member

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    My experience is that summer-time A/C use and winter-time Heater use both reduce fuel economy quite abit, with mild spring / fall mileage being highest because neither A/C nor Heater are being used.
     
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  20. Coast Cruiser

    Coast Cruiser Senior Member

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    I guess I'm strange. (No surprise, right? :LOL:) Not the "typical" Prius driver.

    Comfort (and safety) comes first, not MPG.

    Lights on, always. And I'm going to run the heater or the air-conditioning as much as I please.

    I bought a Prius so that I would not have to be concerned with gas mileage. Truthfully, I rarely even think about it! Anything over 40 mpg is great! I'm not going to become obsessed, or paranoid, or start tracking every last ounce of gas. No offense to anyone, but some people really take it to an extreme.

    I already knew that a Prius gets great gas mileage. I find no reason to keep tracking it or charting it every day. Or every week. I guess for some people it's a hobby? To each his or her own. I only look at my MPG once a month, (or every other month) when I fill up. That's about it. :D And I am very blessed, and thankful, that I can buy gas anytime I need it, without financial worry.

    It's kind of funny, really. People waste so much money in other parts of their lives, but yet they are concerned about using a couple more gallons of gas by turning on the lights, or their heater, or the AC!?

    My Prius is great. Even when the seat is sinking.... I don't analyze it, I just drive it. :ROFLMAO:
     
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