I got my first 60MPG tank, and it is only the second tank I've had in the car, so I am very happy

553.2 mi @ 63.6 MPG

I filled up 8.34gal which calculates to 66.35 MPG. I was a bit disappointed it wouldn't take more gas, but I wasn't going to risk an overfill, so when it stopped pumping I left it at that.

I have a few really good trips of 16+mi:

8/16 - 16.1mi 73.60 mpg
8/17 - 16.2mi 71.03 mpg
8/27 - 16.1mi 76.90 mpg
8/29 - 16.2mi 70.66 mpg

I drove a total of 19 days on this tank at 29.12 mi per day.

During this tank ScanGuage II reported 60.5 mpg, which is off by about 5.19% so I have adjusted accordingly.

Standard deviation for this tank was 5.14 mpg.

Here is a picture before I filled up at the station:

 

Excellent!

The trick on the 600 mile tanks is to have a spare can so you can drive into the 'blinking' fuel indicator. BUT this is not for everyone and having done it over a dozen times, safe enough if you can avoid being in 'a bad place' . . . like a one lane road without shoulders . . .

You realize that 60 MPG is actually the EPA projected city mileage for your model Prius. So you're driving right. As you get more experience, you'll see performance rise even higher.

Bob Wilson

 

Thanks Bob.

I was driving on the blinking indicator for the last 3-5 miles. It came on during my commute to work, so I detoured to the gas station down the street. I realize I probably could've gone home [16mi] without worry, but not having a spare tank in the trunk ready to go, I didn't want to test it.

What gets me is I filled up 8.82 gallons last time, and I only burned 8.7 on this tank. So then when I filled it up, I only filled it to 8.3... So not only should I have had 0.12 gallons from the previous tank, I should have an additional .4 from the current tank that went unburned.

If that is all correct and I didn't lose it to evaporation etc, I should've been able to go at least another 35mi, not including any unknown gas in the tank.

Still, 11.9-8.3 = 3.6 gallons unaccounted for.... Why such a large figure? In theory if I had that much gas in my tank I could've driven much longer. But I know the flexible fuel bladder makes this a difficult estimation.

I figure at worst the bladder may have about a 1 gallon inaccuracy, so that puts me at 10.9 gallons, yet I only filled 8.3

 

The first time I ran out of gas, I went 140 miles on 'blink', nearly three gallons. Since then, I've been getting about 60 miles or a little over one gallon remaining. I can't be sure but I suspect part of the variable fuel tank 'gets cleared' when you first run the tank to empty or near empty. Thereafter the flash seems to be closer to the real empty than it was before. NOTE: I aways have a spare can in the car when approaching 'blink' levels, the last 1/4 tank.

Bob Wilson

 

Hmm, that is interesting.

So how do you officially know you are plum out of gas? Is there an indication that you have zero fuel left? Obviously you go into electric only mode, but other than that, any indicators or warning lights etc?

 

The MFD will show an error that pretty well takes the whole display. You will be speed limited and should get below 42 mph as quickly as safe and slower is better. Hit your flashers and drive to a safe place to add the gas. It may look horrible but the key is to reduce speed, set flashers and get to a safe place to add the gas and park.

After you add the gas, the car will start and the displays will return to normal. With a known amount of gas, drive efficiently to your gas station of choice.

Bob Wilson

 

Thanks Bob.

So are you able to fill up more gallons since your initial empty run?

 

For the first year or so, I would top off the tank on Friday and Sunday evening. This twice a week top-off cycle allowed me to keep my weekly commuting mileage separate from my weekend, longer trip mileage. But I've got enough data to no longer need bi-weekly fill-ups. It also demonstrated the variable part of the tank fill-up seems to be associated with having a substantial amount of fuel kept in the tank all the time.

When I started my gas studies, I started going to either whole tank and/or 4 gallons to 'ran out of gas' mode. Running close to empty seems to have 'cured' the variable tank problem so now my tank receipts, I've always used manual mileage calculations, and now it looks like I have lost the variability I'd seen before. Click on my signature block to see what I mean.

Note there is one entry that shows 14 gallons. I had a full tank and also a 4 gallon sample tank but I'd screwed up on my record keeping. Since I had the mileage for both, I added the two and it looks like 14 gallons. I've never gotten more than about 11 gallons and change into the tank.

Bob Wilson

 

Very interesting, thanks Bob.

I think you are on to something with what you've suggested.

One additional question: Is your low fuel warning coming on at the appropriate point now and is your fuel gauge more accurate?

 

That is hard to say because I'm not recording any data about how far I go on 'flash.' What I remember is the first time I drove on "flash" I went about 140 miles (and was wondering when will I run out.) Most of the others were in the 60-70 mile range. I had one just under 50 mph but we were in a heat spell and I'd had to use the AC heavier than normal. That was the only one that surprised me because I avoid limited access roads when I think I'm within 20 miles. I was just approaching the worst interchange in Huntsville when I ran out. But fortunately there was a nice shoulder and it wasn't during the Huntsville "rush minute."

Otherwise, the fuel gauge has the ~180 miles on first pip. Then between 4 and 6 pips, it seems to drop more rapidly than the others. The last pips, 7-10 seem somewhat more linear. But I still treat the fuel indicator "as a suggestion" versus anything accurate.

Bob Wilson