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Is this strange or normal?

Discussion in 'Gen 3 Prius Technical Discussion' started by cnc97, Apr 26, 2018.

  1. cnc97

    cnc97 Senior Member

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    So I keep an eye on my consumption on the HSI from fill up to fill up. The latest tank of fuel, my 2010 with 212k miles started the tank showing 45.1 mpg (actually first “trip” showed 86.9 mpg due to just 1.9 miles of electric only driving. But over the past three to four days, it’s slowly increased. Today it’s up to 49.9 mpg. The weather outside is warming up slightly, but the ICE seems to be running just as often. I know that things like running the heater make the ICE run more often and “kill” mpg. But it just seems strange that this tank, at 200 miles in, the average is up nearly 5 mpg. And the HSI is about 2.4% optimistic over the 1500 miles that I have owned the car.

    Don’t get me wrong, I love the car and the mileage; but is the warmer(60’s instead of 40’s)temp wise doing it??
     
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  2. Mendel Leisk

    Mendel Leisk Senior Member

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    Warmer temps will improve mpg, both due to simple increase in efficiency at higher ambient temp, and because the car's programming will detect higher ambient temps, and likely change warm-up protocol.

    Another tidbit: I've found with the car half-warmed, if I come to a stop at a red light, and the engine continues to run, if I simply turn the cabin temperature down a few degrees, or shut the vent system off, it'll often tip the engine to shutting off. This is basically the car's programming at work: if you want warmth it'll keep the engine running, discontinue that request and it shuts down.

    Green light, I'll tap the vent system back on.
     
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  3. 04priusnow

    04priusnow Active Member

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    i have seen about 42 to 45 mpg... rear brakes started squealing... down to wear indicator.. replaced and greased guide pins.. checked front.. passenger side guide pins were rusted and no longer float.. rebuilt.. now back over 50mpg.. happy days.. so might want to check yours.. mine has almost 160k..

    PH-1 ?
     
  4. Mendel Leisk

    Mendel Leisk Senior Member

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    Careful with 3rd gen caliper piston orientation on rear brakes. It is critical, to avoid dragging brakes. There's a picture in the attachment. You want the piston correctly oriented, and well-seated against back of pads. For good measure, after a rear brake job and test drive, re-raise the rear and check that the wheels spin semi-freely.
     

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  5. cnc97

    cnc97 Senior Member

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    As the week ends, and next week begins, Southern Indiana temps will continue to rise to nearly 80. I’ll keep an eye on it and see if the increase of mpg continues. I wonder in part also if the increase is due to me adjusting to how the car performs in city driving. I feel like the past seven weeks that the car has been teaching me to be a better driver too.
     
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  6. Mendel Leisk

    Mendel Leisk Senior Member

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    CBC radio this morning said yesterday's high in Chilliwack (a little inland from Vancouver) was 29C (84F), a new record for that date. It's supposed to be much cooler and rainy by the weekend.
     
  7. bisco

    bisco cookie crumbler

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    when does the gas formulation change?
     
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  8. cnc97

    cnc97 Senior Member

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    Here in Southern Indiana they changed the last week of March at the “top tier” stations. The mom and pop stores have been changing since the middle of the month.
     
  9. cnc97

    cnc97 Senior Member

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    This happened on my way home this evening. And I gained three tenths on top of that during the drive. No heat, no AC. Sunroof only open.
     

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  10. bisco

    bisco cookie crumbler

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    best way to track historic mpg's is by the tankful. smooths out the rough edges.
     
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  11. cnc97

    cnc97 Senior Member

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    Since I bought the car in March, the economy has been trending upward. 45.1, 45.9, 47.1, and 47.3 on the previous fill ups. On the next fill up, I’m going to the same mom and pop that this tank came from, just to see if it has something to do with fuel quality. But one would think that a mom and pop would be a “lower” quality fuel.
     
  12. bisco

    bisco cookie crumbler

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    don't know, but trending upward this time of year is completely normal.
     
  13. cnc97

    cnc97 Senior Member

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    It’s been another tank of gasoline since I’ve posted and I thought I’d post an update. I got a bit less mpg last tank, but I found that the station that I fueled at was selling 20% ethanol in their gasoline. Most pumps in my area have the 10% disclaimer which is fine. This particular station had 20%. It triggered the CEL for lean codes, and I took it to a shop that could test the fuel composition. 21.3% is where it came up.
    I have since found a station that sells 0% ethanol, but they get a premium price at $.45 more per gallon. The car loves it. Very happy and the CEL is gone.
     
  14. Mendel Leisk

    Mendel Leisk Senior Member

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    Was the offending station advertising that gas as 20%. I thought the limit was 10%, without special warnings. If not, grass them out. :mad:
     
  15. cnc97

    cnc97 Senior Member

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    It was my local Walmart gas station, actually owned by Walmart and not Murphy USA as some of them are. The local store management claimed to be innocent. Higher levels of management at the corporate level said that my claim was not possible. My car knows the difference, and if you can read the evap/purge percentage, you can test your own alcohol content of your fuel.

    I will say that tank 2 of the ethanol free is netting 57 mpg on strictly in town driving. I drove it 125 miles and put 2.18 gallon of fuel in it. I can’t believe the dramatic improvement the lack of ethanol made. A nearly double digit increase on E0 gas, I would say the price premium is worth it.
     
  16. Mendel Leisk

    Mendel Leisk Senior Member

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    This is ethanol free regular gas? I THINK we got a tank of that up the coast once, the car loved it, whatever it was, hands-down the easiest good mpg tank we had. I think we've done slightly better on one, but this was nothing special, a lot of it was just tooling around town.
     
  17. cnc97

    cnc97 Senior Member

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    There are three stations in my town that sell 100% ethanol free gasoline. Two are public, the other is Pacific Pride Commercial fueling. The two public ones sell the E0 at $.35 higher per gallon. I just wonder if my other vehicle would see any improvement in burning the E0 fuel. Since it only gets 14 mpg in town, it won’t take as long to burn out the contents of its tank. LoL
     
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  18. RRxing

    RRxing Senior Member

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    From Wikipedia:
    1.5 gallons of ethanol has the same energy content as 1.0 gallon of gasoline.
    The energy content of 1.0 US gallon of ethanol is 76,100 BTU, compared to 114,100 BTU for gasoline.

    Gotta keep the corn lobby happy, to the detriment of car owners... :(
     
  19. Mendel Leisk

    Mendel Leisk Senior Member

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    Here's a calculator, seems to work. The yellow highlighted cell has the highlighted formula:

    upload_2018-5-29_12-23-23.png

    Addendum: Added one more field, the BTU drop in percent, compared to straight gas:

    upload_2018-5-29_12-28-36.png

    Attachment updated too:
     

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  20. RRxing

    RRxing Senior Member

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    I think your last calculation is off - Should be a 9.667% reduction. Gotta watch that decimal point