calculated vs. computer MPG - Please post your results

Here are my 2nd-5th tanks on my 2011 Prius (mfg 7/11):

Actual/Reported:
42.45/44.7
44.29/46.2
45.32/47.9

It's slowly getting better but still not quite to my expectation. I upped the tire pressure from manufacturer spec to 42/40 for this last trip, seemed to buy me a couple MPGs. I've been trying pulse/glide whenever I can and trying not to exceed the eco bar.

 

Ok. Just did my 517 mile round trip, all highway. My computer said 56mpg at fill up and the math worked out to be 53.9mpg. I refueled after driving 495 miles. I drove to my destination manually, gliding down hills, staying in the ECO range, etc. my computer should 57.7mpg. On the trip back home I used cruise control all the way, with the exception of disengaging occasionally down long hills when it wanted to brake to keep my speed constant. Most of the trip back was with less fuel (weight) than when I started. I averaged my 56mpg computer mileage with the computer mileage from fill up to back home (added the weight back) and got almost exactly the same mileage.

My conclusion is that any extra mileage I may have gotten, however slight, was offset from me not having to diddle with pedal pressure and constantly watching readouts while driving without cruise.

Granted my car has less than 1000 miles but all things were equal.

Just my .02 worth.

 

Funny you mention that. I was driving home from Birmingham AL to Atlanta today. Couldn't find a gas station for what seemed like 30 miles on a dead stretch of the highway and my gas gauge was on 2 bars the whole time. I'm starting to sweat thinking about how embarrassed I'm gonna be running out of gas in a Prius. My computer says I have 79 miles left but who knows, right? Finically find a station and at 495 miles on my trip meter, it takes 8.3 gals of gas. With an 11.9 gal tank I still had over 3 gals left in the tank!! I could have made it all the way back home with a gallon to spare. Doing the quick math, I got just over 600 miles on that tank. It was my first real fill up since the tank I got from the dealership.

 

? so the trip meter was not set at fill up. I guess I always reset trip b when I fill up. if you got 60o miles on 8.3 mpg is 72 mpg that is great.

 

No. I was extrapolating from what was left in the tank when I already had gone 490+ miles.

495+3.6 gals left in the tank before I refilled.

Figuring conservatively and rounding down that would be 490+180 (3.6x50 mpg) =670 highway miles per tank.

 

What do you mean by 42/40? I noticed when I aired up my tires both to 42, the front were 40 and the rear were a little less. I'm thinking 36 or 38.

 

I meant 42 psi front and 40 psi rear.

 

Our VERY FIRST fillup! All in-city driving by both wife and I:

50.6 MPG = 445 miles/8.794 gallons ("first-click")
51.7 MPG from dashboard (MFD) display, which is 2% optimistic value.

Fuel gauge had two "pips" showing.

 

I found my dashboard to be optimist as well according to the actual math. I'm on my 2nd fillup. After about 150 miles I reset trip a and left trip b alone. I switch between the 2 and they never match up. The one with the least amount of miles seems to be consistently about 3-4 mpg less from trip to trip and I am driving exactly the same route to and from work. Seems to be like my GPA from college. Early on you can make up a C with an A. The more hours you take makes it to where it takes 5 A's to make up the same ground lost from a C.

 

So, has anybody determined the empirical relationship between gas-gauge gallons and pips?

My 'pencil-on-napkin' mental analysis says 11.9 gallons total capacity, less ~1.9 gallons for "reserve" ('flashing' pip), leaves 10 gallons of "usable" fuel...or, roughly, 1-gallon of gasoline per pip. Of course, there's the question of "linearity" between FULL (10·pips) and EMPTY (1·pip 'flashing')...which is close, but not 100% linear.

So, my WAG is that 1·pip ≈ 1·gallon ≈ 45-50-55 miles...as a rough guess-ti-mation.


• Addendum:
pip = single, one-of-ten, segment/bar on fuel level display
PiP = acronym for Plug-in Prius.

 

What's a pip?

 

a Plug In Prius, but in regards to the fuel, its one little bar on the fuel gauge...

 

Thanks. I thought so but am still learning all this new Prius acumen

 

Acronyms-R-Us...welcome to world of brevet brevity.

 

4 years and 91260.9 miles tracked

Displayed = 63.7 mpg
Calculated = 60.2 mpg
Difference = 5.8%

 

Our second fillup, all city/urban driving by both wife (lots of A/C) and I:

48.5 MPG = 449 miles/9.253 gallons ("first-click")
50.6 MPG from dashboard (MFD) display, which is 4% optimistic value.

Fuel gauge had one "pip" showing.

 

My 5th fillup also with a/c.

Actual. 45.96mpg
Dashboard (MFD). 50.1mpg

Just over 9% optimistic.

Interesting as the first 4 tanks were fairly close to being between 2-3 mpg apart. Also, I have been playing with different routes to and from work this tank.

 

The MFD on my 2005 Prius seems to overestimate MPG by about 3%. From what I've read, this is very average for GenII Prii.

 

First fill up with my new to me 2010 116k mile Prius II was 54.6 MFD and 54.19 actual on a 504 mile tank. Better than I expected. Loving this thing so far.

LG-VS980 ?

 

Our third fillup, all city/urban driving by wife (lots of A/C):

49.4 MPG = 478.3 miles/9.674 gallons ("first-click")
51.7 MPG from dashboard (MFD) display, which is 5% optimistic (same as previous fillup).

Drove 13 miles with last fuel gauge "pip" flashing (465-to-478 miles). Looks like the 'flashing' begins when the fuel level reaches 20% of the tanks' 11.9 gallon capacity, ie: 80% ≈ 100%*(9.52 gal. / 11.9 gal.)