calculated vs. computer MPG - Please post your results

I believe I have some valid information to share on MPH Indicated vs Hand Calculation. I have a 2010 (Version 4) built 05/2009, with 49,000 miles. I have calculated each tank of fuel since 6/27/09. This time period represents 134 calculations. Fueling was stopped on the first click. Without exception, the FCD vs hand calculated MPG runs in the range of 3.4%, higher than the hand calculation. I believe this number to be very accurate. I live in LA with fair weather driving 100% of the time. I estimate from my records that I average around 48.5 mph. This is the first time I have posted in a number of years and I hope this adds to your data bank. I have another significant situation to to share with you about what happened after an EFI procedure was performed, but I don't know if this is the correct Forum to present it in. Please let me know.

Linkster

 

Last fill up....

Trip data on Prius said I got 58.8 mpg. Math from gassing up said 55.6.

 

Prius C 2012 over 5000 miles and 13 fuel ups , Car says 57MPG Fuelly says 51.4MPG

 

• 58.8MPG(mid)/55.6MPG(tank) = 1.058 ≈ 6% optimistic (high)

•57.0MPG(car)/51.4MPG(tank) = 1.109 ≈ 11% optimistic (high)

Those are rather widely varying numbers.

 

I got the update and noticed ever since then I fill up my tank and says I have about 420 miles until next fill. I do t get how everyone is getting up to 500+ miles. I have a 2013 Toyota Prius 5. I believe it's the gen 3.

 

61.3 on screen but Real Math 59.32

 

Just filled up my first full tank on the new Prius.

535 miles - Computer = 60 mpg / Calculator = 55.7 mpg

 

I don't think I've ever looked at that gauge. If you want to track your mileage:

1. Develop a consistent fill-up style. I'd recommend to pump 'till the pump shuts off, then stop.
2. Note the odometer reading. Regardless of what gauges or showing, whenever you shut off the car this number will persist, for about 30 seconds.
3. Repeat #1 and #2. This'll give you distance travelled and fuel consumed, the two factors of calculating miles per gallon.

 

Our early version 2010 Prius IV, purchased in June, 2009, has had 141 fill-ups over 54,373 miles (odometer reading at last fill-up). Lifetime calculated mpg = 46.8; lifetime display mpg = 49.5. Every fill-up ends when the pump auto-stops. Most of our driving consists of short, 5 to 6 mile trips around town, with occasional long, interstate trips of several hundreds of miles a couple of times each year.

 

ALL the above MID-vs.-calculated (tank) MPG numbers simply AMPLIFY my original contention that the MID-calculations performed by the computer in the Toyota Prius are OVER-estimating fuel economy...for whatever reason...and doing so rather consistently.

Why this is happening, I have no idea, but with the help of a ScanGaugeII™ I was able to determine that the major cause of similiar problems with our 2011 Cruze LTZ was the result of how long the engine was staying in 'open-loop' A/F-operation (during warm-up) before switching to 'closed-loop' A/F-operation (normal engine temp & operation). There was an almost 1-to-1 correlation between the MPG ±error and the length of 'open-loop' operation--the longer the 'open-loop' time, the more the MPG error.

 

My last 2 fill ups the computer read approximately 3 mpg more.
-Computer: 53.8, calculated: 50.82
-Computer: 52.7, calculated: 49.76

 

Well I just got 320 miles on a tAnk. And it was like33 or 34 mpg!! Which I know something is wrong. I think a Honda civic gets more. Lol and I see people on here saying there driving over 500 miles on a tank of gas. When I first got it and I would fill up the car would tell me I had 520+till next fill up. And I know it could be more or less depending on how u drive and blah blah!! Now I fill up and it says 420 or 405miles till empty tank and it's really getting like 320 or sometimes a little more. This really is annoying. It happened ever since the update. I JUST WANT TO KNOW WHEN PEOPLE FILL UP THERE TANKS HOW MANY MILES DOES IT SAY TILL MEXT FILL UP!!! It's not a hard question . NOBODY SEEMS TO ANSWER IT. !!

 

Mine says 540 to 550.

 

Just fuelled up my Prius for the second time(about 440 miles between fuel ups), 56.0 computer vs 52.8 fuelly, difference of about 6%.

 

What's amazing about the mpg comparison is that in almost every post there is a difference of approximately 2 to 3 gallons, where the Prius computer is on the higher side. I can understand it if the gap is all over the place but because of the slight, consistent, it seems that the computer put in the Prius is pretty much calibrated the same for all models, and for most years.

 

Which is the basis for my two-word summary: Consistently optimistic.

 

For my last tank of gas...

Computer: 4.0 l/100 km
Calculated: 4.25 l/100 km

6% optimistic

 

Just filled up my tank today.
Car computer 59.9
Actual 56.5

This was with pure gas not that E10 Cr@p.

 

Apparently, nobody (as yet) has felt the need to monitor & record that information; I know that I don't and haven't.

Why? Because that information is based upon the PAST mpg the engine computer calculated, which is NOT truly applicable to what's GOING to occur in the future...although it *IS* a better "guesstimation" than nothing-at-all.

 

IIRC, at a full top off, my rating is just over 600 miles.