Calculated MPG vs. Indicated MPG of the c - Please post your results

Thanks, everyone, for posting these results. I was a bit surprised at first to see they were relatively "low", but it looks like many folks are just driving it normally, trying perhaps to be aware of driving technique somewhat but without huge efforts to hypermile, with a few exceptions. The fact that everyday driving nets 50 mpg fairly easily is great, and 60 mpg with a little work is great. I would bet 70 and 80 wouldn't be too far out there in warm weather for some folks. Wonder if the local Toyota dealer would let me have one for a week

Oh, and on topic, glad the calculated isn't too far off like Gen III

 

Aaand my 3rd fillup:

Year of vehicle: 2012
Date: 5-19-2012
Miles driven: 552
Gallons Pumped: 8.98
Hand-Calculated MPG: 61.4
Displayed MPG: 62.8
Average Speed: n/a
Tire Size / Wheel size: 15"
Tire Brand / Model: Goodyear/Assurance
Tire PSI (Front / Back): 42/40
Seasonal Conditions: in the desert so have already been in the upper 90s with A/C usage on maybe a fourth of the tank (mostly with thermostat at 76, accidentally had it at 60 for about 15-20 minutes).
Commute Length: variable
Hypermiling Techniques: Pulsing followed by exuberant use of cruise control, gradual/regenerative braking, coasting down hills.
Other: more short (<5 mile) trips than I care to admit, yet I still bested my two prior fillups.

 

1st tank of gas: 55mpg indicated, 53mpg actual.
2nd tank of gas: 57mpg indicated, 55mpg actual.

A trend developing?

 

1st tank is 52.3 computer calculated, and 50.2 actual.

My second tank is so far higher, 57mpg calculated, and I'll update in a few days

 

Does anyone have a longer term comparison number (i.e. for the last 5386 miles I've put in 100 gallons of gas for a 53.9 calc mpg, the displayed MPG over that timeframe reads 55.1 MPG)?

For my car, I keep a spreadsheet going and calculate the gallons of gas my car "thought" I used when I drove (i.e. 630 miles, display said 63.0 mpg therefore the car "thought" I used 10.0 gallons of gas). By doing that I can total all my mileage and all the gas the car "thought" I used and come up with a lifetime HSI MPG Value.

For my liftback my calculated average is 59.6 mpg, the HSI MPG lifetime would be 63.0 mpg)

 

Year of vehicle:2012
Date: May 24, 2012
Miles driven: 533 miles
Litres Pumped: 8.68 gallons
Hand-Calculated mpg: 61.4 mpg
Displayed mpg: 62.2 mpg
Average Speed: -
Tire Size / Wheel size: 15"
Tire Brand / Model: Goodyear Assurance
Tire PSI (Front / Back): unknown (Dealership levels)
Seasonal Conditions: ~60-70F, some Sun, some Rain
Commute Length: 74 miles (round trip), two lane
Hypermiling Techniques: Gliding, Careful driving, Conserving momentum, Hill techniques
Other:

 

My first fill!
BP gasoline, regular

Year of vehicle: 2012
Date: 5/31/2012
Miles driven:
Gallons Pumped: 8.88
Hand-Calculated MPG: 57.5
Displayed MPG: 59.3
Average Speed:
Tire Size / Wheel size: 15"
Tire Brand / Model:
Tire PSI (Front / Back): 42/40
Seasonal Conditions: AC @ 73F during afternoons.
Commute Length: 54 miles
Hypermiling Techniques: Eco Mode ON

 

Year of vehicle: 2012
Date: 06/02/12
Miles driven: 465.0 miles
Gallons Pumped: 8.486
Hand-Calculated MPG: 54.91
Displayed MPG: 55.4
Average Speed: approx 38,reset before double checking
Tire Size / Wheel size: 15" stock
Tire PSI (Front / Back): 39/37
Seasonal Conditions: very warm week, AC on 75% of the ttime, auto set to 73-74 degrees
Commute Length: 55 miles
Hypermiling Techniques: none
Other: This tank was almost all given to my work commute. About 110 miles each day. Was really hot at the beginning of the week then gave way to heavy heavy rain on Friday. 70% highway at 55-65mph I'd say. The rest traffic

 

Over 14 fill ups my MID has consistently reported +2 MPG over my calculated MPG.

 

after 2 fillups MID has reported +2-3 MPG vs my calculated MPG

 

Prius C CDN base model (USA C 2) from Modo the Car Co-op - I filled up, drove for about 160 km, filled up again. I calculated 4.31 L / 100 km, and the car reported 4.3 as well.

 

I have filled up twice since my last post. Here they are.
Year of vehicle: 2012
Date: 5/25/12 --- 6/4/12
Miles driven: 485.6 --- 503.5
Gallons Pumped: 8.504 --- 8.619
Hand-Calculated MPG: 57.10 --- 58.62
Displayed MPG: 59.0 --- 60.0
Average Speed: Failed to check both times...
Tire Size / Wheel size: 15" stock
Tire PSI (Front / Back): Still not sure...I really need to check this out soon.
Seasonal Conditions: Weather was mostly sunny, mid 60s to high 70s.
Commute Length: just over 30 miles round trip (twice a day). More, if I need to stop at a store, or the bank along the way.
Hypermiling Techniques: regenerative breaking and some pulse and glide.
Other: Before the first fuel-up listed here, I went on vacation for about 2 and a half weeks and left the car with the fuel light flashing. My father drove it once while I was gone, for about 7 miles. When I got back, the fuel gauge read two bares...I found this most interesting, especially since my father insists that he didn't add any gas to the car while we were gone. Perhaps it was the warmer temperatures while we were gone...

 

Year of vehicle: 2012
Date: 06/02/12
Miles driven: 443.5 miles
Gallons Pumped: 7.60
Hand-Calculated MPG: 58.4
Displayed MPG: 60.0
Tire Size / Wheel size: 15" stock
Tire PSI (Front / Back): 39/37
Seasonal Conditions: fairly warm, but to improve mileage I sweated it out with minimal AC
Commute Length: 55 miles
Hypermiling Techniques: just trying to run on EV whenever I could
Other: This tank was almost all given to my work commute. About 110 miles each day. Was really hot at the beginning of the week then gave way to heavy heavy rain on Friday. 60% highway at 55-65mph I'd say. The rest traffic

Last two tanks were ran on pure gas, but because of the decrease in E10 in the area I'm going to switch back on the next tank.

 

Back again with fill-up #4, and it's my worst since the first, ugh.

Year of vehicle: 2012
Date: 06/07/2012
Miles driven: 599.9 (the first 600-mile tank?)
Gallons Pumped: 10.002 (so much for a 9.5 gal tank. Must've been running on fumes when the battery wasn't engaged. I was EV'ing like a mofo in order to reach the sole distant station with pure gas to fill up)
Hand-Calculated MPG: 59.98
Displayed MPG: 64.8
Tire Size / Wheel size: 15"
Tire PSI (Front / Back): 42/40
Seasonal Conditions: A/C estimated usage 25% of the tank, windows or fan the remaining 75%
Hypermiling Techniques: same as previously

Other: A nearly ~5 mpg discrepancy between calculated and displayed, the biggest yet IIRC. I have been topping off the same each time (a single top-off), so it must be down to differences in gas station pumps. The next calculation will be based on ethanol-free fuel.

 

You think it gets less accurate when it's spitting fumes to keep the car going? Ace job though, 600 mile tank!

 

^May be! It's probably something I shouldn't try to repeat on a regular basis (it's the first time I filled over the rated capacity of 9.5 gallons). I didn't notice any sputtering fortunately.

 

Year of vehicle: 2012
Date: 6/5/2012
Miles driven: 396
Gallons Pumped: 7.43
Hand-Calculated MPG: 53.3
Displayed MPG: 54.6
Average Speed: Not recorded
Tire Size / Wheel size: 175/65/15
Tire Brand / Model: Bridgestone/ Stock Turanza tires
Tire PSI (Front / Back): 41/39
Seasonal Conditions: Warm and dry with some highway driving and some AC use
Commute Length: 4 miles each way (about 50% of the miles)
Hypermiling Techniques: Still learning

I went exactly one month between fill-ups. I used the same filling station, but not the same pump. I filled to the first pump shutoff each time. Hopefully I filled to the same level each time. This was my second fill-up, so the dealership does not factor into the calculations.

The mileage value = (actual fuel delivered by the gas pump / miles driven) ​

The displayed value = (estimated fuel delivered by the fuel injectors / miles driven) ​

​

Those values really should not be the same. It is remarkable they are even close.

The hand calculated value includes ALL fuel consumption, not just fuel injector delivery. It includes fuel losses to diffusion through fuel lines, pumps, and seals. It includes evaporative losses during refueling and daily heating/cooling of the fuel tank and gasoline (most of this vapor is captured by the ORVR/EVAP system). It includes fuel delivered to the engine via the EVAP system that does not pass through the fuel injectors.

The gas pump delivered 7.43 gallons of gasoline, which weighs 21.59 kg. The displayed MPG represents 21.08 kg of fuel injected into the engine. The difference is about 0.5 kg, about the volume of a medium soft drink at McDonalds. If I pumped that same gasoline into an open bucket, it would be gone in less than a month. Not only does the PriusC use gasoline efficiently, it is incredibly stingy about retaining the gasoline pumped into the tank.

That 2-4% difference in hand calculated vs displayed MPG is not a deliberate error or mis-calibration by Toyota. It is a testament to the incredible engineering design of the fuel delivery system. As someone that learned to drive in the 70s on the gas guzzling, fume spewing, road hogs of the day, the PriusC is an absolute marvel.


Tom

 

I filled up on 6-7 and now have several fill ups. So far after the initial fill up from the dealership, I have driven 2204 miles on 32.754 gallons or 67.29 MPG. I drive in Fort Lauderdale mostly with some short highway trips. I am conservative in that I drive in ECO mode all the time and use a lot of coasting. My short trips are killing my overall mileage a bit and yet I am totally happy with my mileage.

 

I think they get exactly what they deserve : -)