After 10,392 miles and 26 fill ups my ACTUAL mpg is now 38.92 mpg and my INDICATED mpg is 39.69 mpg.

Last tank was off by almost 2.5 mpg. While it is averaging pretty close over the long haul the large mpg "indicated" tank numbers are really discouraging when they don't actually calculate out that way. I'm still trying to figure out what factors cause the most discrepancy. I still believe the mode where I'm at 60 on the FE gage and using little gas is causing the problems as it is not measuring the gas to the engine at idle accurately. My theoritical gallons used of 261.816 compared to actual gallons purchased of 267.028 is very close considering that's over 10K+ miles.

Still it's pretty incredible considering my 4Runner has used 431 gallons and that's on less than 7000 miles. (It's not getting used much)

 

After 10,392 miles and 26 fill ups my ACTUAL mpg is now 38.92 mpg and my INDICATED mpg is 39.69 mpg.

wvgasguy could this be in part to gas pump error ?So many things to consider;Is your manual calculation vs your readout mpg always off the same? I know the gas pumps are off a little either way,maybe there off more than the cars computer readout? Lets say you put in 10 gallons but got 10.2 and you showed 400 miles driven ,your computer in the car would be working with 10.2 actual gallons but manual cal would be working with 10 to fiqure with. I hope you know what i mean cause this is racking my brain...LOL JOE

 

After 5 tanks, I'm off by about 1.5mpg each tank. You have to realize that our manual calculations are straight-line, meaning we divide total miles by total gallons after the entire tank is depleted. The computer is calculating dynamicly, meaning it is readjusting the overall average based on what you are doing "right now". With so much dynamic calculation over all those miles, there are bound to be rounding errors, etc. I don't know why they don't just do the simple straight-line calculation, since the computer knows when you last filedl up the tank, it should remember the odometer reading and figure it out from there.

 

This is interesting since I drive mine hard (like I would drive any other vehicle) and I am getting anywhere between .1 to .8 MPG higher (ACTUAL), then the computers reading?

I drive 80MPH or more on the freeway for 17 miles and pull a 35degree grade at about 60MPH for over a mile and a half as my regular 5 day commute.

Then again I am averaging between 30.1MPG and 33.7 MPG (computer readings) average depending on traffic and my lead foot .

I usually see the .1MPG greater actual reading at 33.7MPG (computer) and the .6MPG-.8MPG greater actual readings a 30.1MPG (computer).

 

With the regulations and fines for poor measurement I expect the pumps to be a lot closer than my computer. I'm guessing if a pump is off it's by a very small margin.

I am over and under, typically the larger margins are when I show a very high indicated (42+). I just filled up a little bit ago and it's fairly close but I didn't have a lot of "gliding" on this tank.

 

This is interesting since I drive mine hard

I was curious about some of the drivers with lower averages. It is my assumption the the lower the number, the less of the really high FE numbers to add and thus a closer to true average. Somehow I think the gliding and E mode messes up the calculations some. Your observation makes me lean towards that conclusion.

 

The computer is calculating dynamicly
Yeah, I don't get the point (Toyota's). If they have an accurate measurement and the miles are saved electronically why can't the average be accurate? I don't want it assuming anything I just want it to tell me how I've done so far.

Part of the reason for my posting is I looked at the milage database and noticed a lot of people are using the FE indication rather than hand calculating for their reporting.

I'm guessing the 35 to 37's are pretty accurate and the higher you go the more innacuracy. Don't want to burst anyone's bubble, but when I do hit the big "39" I want to know I really got there.

Of course even I have to ignore the speedometer error.

Have you noticed all the "portable" navigation systems show speed (and distance traveled?) but the built in one does not? Hummmm, makes you wonder if they don't want to admit the obvious.

Can't complain though, someday I may just turn this screen off and be happy with 37.

 

I just noticed my last tank took me to 39. However I'm still not there yet, Jason's database rounds up as well.

(I am averaging over 39.5 though for the last 1500 miles, so it's getting a lot better than it did the first 1500 miles)

 

My bet is the most cause is variable filling level.
If you fill at the same pump of the same gas station, the same click stop, the same topping off level, take the same time, say 3 min, and the same ambient temp, you'll see more consistent results.
The incline level beside pump causes a big difference.
My recommendation is the calc mileage becomes more accurate using three fill-ups rolling average than a single fill-up.

Anyway, the computer number is very stable, but it has some steady error about 2% on Prius case.

Ken@Japan

 

[I]My bet is the most cause is variable filling level.[I]

95% of my fills are at the same station. I always fill on flat, level surface. I slow the pump as it gets close to full and let it kick off. I give it two squeezes that kick off (that usually adds avout 2/10ths of a gallon. I don't "overfill" but I try to fill it to the same level as possible by using a consistant fill procedure.

Also my actual gallons used compared to my theoritical gallons used is over 5 gallons and that would be a consistant 0.2 gallons error per refil. I don't think I could be off that much consistantly each time. Occosionally yes, but not consistantly, and if so it should average out.