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What is your DTE after fill-up?

Discussion in 'Prime Fuel Economy & EV Range' started by Salamander_King, Oct 8, 2019.

  1. Salamander_King

    Salamander_King Senior Member

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    I don't think comparing the DTE with actual miles driven from a full tank on regular Gen4 Prius or PP on HV only is the way to find out the accuracy of the HV only mpg based on the DTE. Besides, the DTE is an estimate for driving distance until the empty light comes on. If you fill the tank before the light comes on or drive much further past that point (on PP with a full charge, you can theoretically drive ~130miles beyond the empty light when DTE reaches - - mile), you will never be able to compare the DTE to the actual miles driven. The actual miles driven is affected by the current and future driving conditions, and DTE is based on past performance. Similar to the GOM EV range, the DTE is only a prediction at the best. But what I think DTE is good for is to use the number to estimate "past" efficiency.

    Here is some data I have on using DTE to estimate HV only mpg on my last PP. The number difference between the calculated (full tank method) and DTE estimated is only +3.6% for the one full tank drive I did without charging (no EV drive, 4th row) and -4.8% on the one drive with a single charge (comparing to adjusted mpg, 5th row). For adjusting HV only mpg, I used 5.0miles/kWh for the EV efficiency. I used kWh from the wall for calculating EV miles driven, but this is actually not accurate for some portion of the kWh used for charging from the wall never really goes to the wheels. So more EV drive I have done during the full tank drive bigger the % difference when comparing the adjusted calculated HV mpg to DTE estimated HV mpg (rows 1-3).

    upload_2021-7-27_9-56-23.png
     
    #101 Salamander_King, Jul 27, 2021
    Last edited: Jul 27, 2021
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  2. jerrymildred

    jerrymildred Senior Member

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    Well, you can add the remaining DTE to the actual miles given and multiply the gallons used by the ratio of driven to remaining miles to extrapolate.

    However, I think your system shown in columns B through I in the spreadsheet is a pretty good idea if you can track all the electricity you feed to your car, which I could do, but won't since it's just too much work since I charge at work and sometimes other places. When it's 3,000 miles or more between gas purchases, that's a lot of individual charges to add to the number on my charge meter at home. Cost per mile is still my yardstick of choice since that's the one that hits my wallet and is easy to calculate. ;)
     
  3. fuzzy1

    fuzzy1 Senior Member

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    Um, wouldn't you also be looking at and recording remaining DTE just before fill-up? This way you don't have to fill up precisely when DTE transitions to 0.

    I would imagine this 'sort-of' working in consistent MPG conditions, though not necessarily to the accuracy many people would desire. My problem would be with significantly changing MPG conditions, which I encounter regularly.

    I haven't charted any of this as you have, but would be recording pre-fillup DTE too as part of the calculations.
     
  4. Salamander_King

    Salamander_King Senior Member

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    Humm, here goes a new data collection project for me.:LOL: Nop, I have not recorded pre-fill DTE. I just try to fill the tank as close to empty light, but I admit that I have not always done so.
     
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  5. road2cycle

    road2cycle Active Member

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    This last tank of gas I tried to run the Prime in 100% in hybrid mode. With the exception of about 20 miles that my wife drove in full EV mode, I remembered to switch it out of EV mode before every drive.

    DTE at last fill-up: 520
    DTE remaining at current fill-up: 40
    DTE displayed after current fill-up: 528
    Odometer delta between fill-ups: 479
    EV only miles driven: 20
    Gallons of gas fill-up: 8.58

    Delta DTE / gas = (520-40) / 8.58 = 55.94

    Odometer / gas = (479 - 20) / 8.58 = 53.49

    Current DTE / 9.3 = 528 / 9.3 = 56.77

    What I got out of this sample size of one is that either DTE calculation method provides roughly the same mpg value, and that the DTE predicted value is a bit inflated over actual.

    I was also pleasantly surprised that the engine warmup cycle didn’t consume too much additional gas for city driving that I normally do in EV mode. My average mpg dropped by about 2 compared to previous tanks where city driving was done in full EV mode.

    It was still nice having to fill-up more than two weeks ago, but I’ll be back to charging the Prime and running it in EV mode to squeeze a few extra days in between gas station visits. Regular unleaded was $4.56/gallon where I filled up this morning.
     
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  6. Salamander_King

    Salamander_King Senior Member

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    Thanks for the n=1 data on this. Just for the completeness of the data set. Did you happen to set the trip meter to zero before this tank and checked the corresponding mpg display from the dash at the time you filled it recently? Of course, that number contains ~20mils of EV, but even adjusting for that extra miles, I would think it is even more inflated than the DTE method. Historically, on my previous PPs displayed mpg was 6-7% inflated from the calculated which was also true for my Gen3. I have no doubt our 2021 PP is the same in this aspect.

    Unfortunately, for my 2021 PP, I am currently running it as much on EV as possible to save money. Until very recently, the gas price was cheaper than electricity so that, I was running more HV than EV. That made me refuel more often to get more data points, but now with my driving habits, the refuel interval is likely to be more than 2 mo.
     
    #106 Salamander_King, Aug 10, 2021
    Last edited: Aug 10, 2021
  7. jerrymildred

    jerrymildred Senior Member

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    I guess that verifies @Salamander_King's 9.3 denominator. So from now on, just take the new DTE (528) and divide by 9.3. Guess what you get. You get 56.77 mpg. ;)

    I'm not surprised that it's slightly inflated. I drove 14 consecutive tanks with almost no charging on a 6,000+ mile trip in 2019. The computer inflated the mpg on every tank by anywhere from 2-5 mpg.

    Edit: I went back and looked at the numbers from the trip and the car did not always inflate the mpg. It was anywhere from +3.5 to -2 mpg from actual.
     
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  8. road2cycle

    road2cycle Active Member

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    I did reset the trip meter to zero at the last fill-up, but did not note/record the displayed mpg at the 479 mile mark. As you mentioned, that value would have been skewed by the 20 EV only miles driven. I’ll have to gather that data point the next time I run this experiment . . . and remember to let my wife know not to drive in EV mode during that tank of gas.
     
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  9. Salamander_King

    Salamander_King Senior Member

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    This is the entire driving record of my 2020 PP. The % delta for the mpg displayed vs mpg calculated (this is just calculating distance driven/gal of gas at fill-up without adjusting for EV miles) was average +6.82% inflated on the dash display. But if I do not include the very first top-off fill of 1.7gal after purchasing the car which gave a very accurate but very low mpg with only -0.01% delta, the average would jump to +7.96% inflated mpg display on the dash.

    upload_2021-8-10_14-43-49.png

    That might be the hardest part of your experiment. :ROFLMAO::ROFLMAO::ROFLMAO:
    Easier way would be to not charge the car at all after the fill-up. Of course, you also have to have the EV range depleted before the fill-up. ;)
     
    #109 Salamander_King, Aug 10, 2021
    Last edited: Aug 10, 2021
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  10. Salamander_King

    Salamander_King Senior Member

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    The "9.3" factor came to play because I assumed the empty light first came on at that point leaving ~2 gals of gas still in the tank. This assumption may be wrong. The empty light may come on at a somewhat variable rate. I think I have had the empty light came on and was able to stop for the refill immediately after that and the car took ~10 gals of gas, meaning it was more like 1.3 - 1.4 gals (depending on which spec you are looking at) still left in the tank at that point. So, that would make "10" the magic number.

    From @road2cycle data, if Odometer calculation is the most accurate mpg, then adjusting the factor accordingly would give us a more accurate HV only mpg estimation. 528/53.49=9.871... So, using 9.87 for DTE estimation would have given the accurate mpg. If we have enough samples, we can adjust this number to a more accurate one, but the number is likely to be variable anywhere from 9.0-10.0. Using "9" would give an inflated more optimistic mpg, whereas using "10" would give a conservative more pessimistic mpg value. Maybe we may settle for 9.5 as the best number to use?
     
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  11. jerrymildred

    jerrymildred Senior Member

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    More data. I filled up today so I can start tomorrow's New England trip with a full tank even though it only took just 3.283 gallons to fill it. That was 1,695 miles of driving since early May. (I was out of the country for a month in that time.)

    DTE was 564, which was one more than the last tank and the same as the tank before. Now we'll see how it does on a big road trip with lots of Interstate miles.
     
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  12. Gokhan

    Gokhan Senior Member

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    New DTE record!

    DTE after the eight fill: 750 miles

    Vehicle: 2021 Prius Prime Limited Blue Magnetism (Spirited Aqua Metallic)

    This is the newest PriusChat record! The DTE has increased by about the same amount as the previous increase after the sixth fill (DTE = 715, 732, and 750 miles after the sixth, seventh, and eight fills, respectively).

    [​IMG]
     
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  13. jerrymildred

    jerrymildred Senior Member

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    WOW!!!!
     
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  14. Gokhan

    Gokhan Senior Member

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    New DTE record!

    DTE after the ninth fill: 763 miles

    Vehicle: 2021 Prius Prime Limited Blue Magnetism (Spirited Aqua Metallic)

    This is the newest PriusChat record! The DTE has increased a little less this time (DTE = 715, 732, 750, and 763 miles after the sixth, seventh, eight, and ninth fills, respectively).

    [​IMG]
     
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  15. Salamander_King

    Salamander_King Senior Member

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    Wow, that's impressive. If the 9.3 factor is correct that would be ~82mpg on strictly HV mode.

    Just curious, what is on your ODO and your lifetime MPG on ODO? Of course, the mpg displayed is inflated by EV mode, but it seems you do a substantial amount of HV mode drive.
     
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  16. Gokhan

    Gokhan Senior Member

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    I am not sure what that is, but it's not correct. After the last fill, if I don't subtract the EV miles, I get 85.41 mpg (805.4 miles driven, 9.430 gallons). After subtracting the EV miles (corresponding to the SOC use), I calculated my actual HV mpg to be ~ 72 mpg, but this doesn't take into account any odometer calibration.

    About 85% of my driving is purely HV driving, and about 15% is purely EV driving.

    Odometer and trip meter are showing 89.2 mpg and 89.1 mpg at 6657.1 miles, respectively. It looks like the MFD mpg values are exactly 5 mpg overestimated according to what I have been observing.

    [​IMG]
    [​IMG]
     
    #116 Gokhan, Oct 2, 2021
    Last edited: Oct 2, 2021
  17. Gokhan

    Gokhan Senior Member

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    New DTE record by a nose!

    DTE after the tenth fill: 768 miles

    Vehicle: 2021 Prius Prime Limited Blue Magnetism (Spirited Aqua Metallic)

    This is the newest PriusChat record! The DTE increased very little this time (DTE = 715, 732, 750, 763, and 768 miles after the sixth, seventh, eight, ninth, and tenth fills, respectively).

    [​IMG]
     
  18. Salamander_King

    Salamander_King Senior Member

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    WOW! That's amazing. Is your regular driving distance always substantially longer than the EV range?

    I use to drive on HV more often even for the shorter distance because gas was cheaper, but now the gas price is higher than electricity. I am doing most of the drive on EV. That leaves only very few occasions, often on high-speed highway drives for HV mode. I have to burn some gas I have in the can for my generator so I can refresh the stock for the winter. I should be refilling the tank soon for the third time in ~3500 miles.
     
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  19. Gokhan

    Gokhan Senior Member

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    I put about 85% SOC once per week, charging it once a week from about 15% to 100%. I have been driving for about 650 miles a month; so, it is mostly HV driving.
     
  20. Salamander_King

    Salamander_King Senior Member

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    Is that because your electricity rate is exorbitantly high? Even with your hypermiling 85mpg or above efficiency on HV mode, from what I have heard on the price of the gas in CA, I think if your trip is routinely shorter than say 40miles total per trip, driving on EV mode most of the time would be cheaper, wouldn't it? Our gas price is currently at $3.35/gal. At this price and compared to unchanged $0.21/kWh electricity rate, even if I get an average of 85mpg on HV mode, EV mode with 35miles of the range is cheaper. HV is $0.054/mile vs. EV is $0.039/mile.

    BTW, this number was completely opposite not too long ago, when the gas was near $2/gal. No matter how much I could have extended EV range, the HV was cheaper.
     
    #120 Salamander_King, Oct 29, 2021
    Last edited: Oct 29, 2021
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