steverhode

I have been carefully checking at each fill-up and comparing the MPG the car gives ("Tank Avg") right before I fill up with what the actual number turns out to be based on actually miles driven and gas used.

The bottom line is that my 2008 GS350 consistenly over-estimates my mileage by .5 to .7 MPG, i.e. I'm getting about 17.7, while the car says 18.2 to 18.4.

I'm not surprised it was off some. I am surprised it consistently does it one way only (over) rather than and being off both over and under.

I'm just curious if this is typical for the estimate to be on the high side and about that amount.

ecount00

I'll track mine and see what i get. I know i've seen other posts about this so others will be able to chime in. i recall some of the other deltas being more than .5 mpg. Actually, i think i'll be happy if it's within 1 mpg. or at least will feel like it's good enough for my purposes.

socalJD

It's hit & miss with me - it alternates b/w +/- .5 mpg with each fillup (ie -.4, +.5, -.4, +.3) I'm consistent with my fillup process, after the pump clicks off the 1st time, I top off to the nearest whole dollar (at current prices, less than 1/4 gallon topoff). I'll see if the alternating trend continues, my communte is fairly consistent.

larrs

I've had mostly the same results as steverhode. In 105 fill-ups, there have been only 3 times when my calculated mpg is higher than the computer's. Over 26,000 miles, I've calculated an avg 24.4 mpg while the computer avg is 25.4.

The G Man

I also did manual calculation on fill ups. Actually, the GS's mpg computer is pretty close. On my last car, the GX470, the mpg computer was consistantly 1 to 2 mpg higher.

TXprfrmnce

iTrader: (1)

I am impressed someone knows the exact number of fill ups they have had since owning the car!

rkb43

I would bet the computer in the car is accurate.
Wouldn't you have have to fill up from the exact same pump at the exact same temperature every time for your manual calculations to be a valid comparison? Since you are actually calculating based on volume pumped and the computer is measuring fuel burned I would expect some variation, since the volume gasoline occupies is temperature dependent.
Just kind of thinking out loud on this one.

larrs

Yes, I thought so too; but I expected the variation to both + and - (e.g., summer vs. winter). The fact is that the computer is for all intents and purposes always higher. So unless the various stations are consistently charging for more gas than they are pumping, I can't explain it.

The G Man

Every car I have driven with a MPG computer have a higher MPG reading than actual.

socalJD

^ My 2IS was consistenly apprx .5 mpg lower than actual (using the same fillup process as the GS) For the life of the IS (apprx 17k miles) I had a avg of 22.5 mpg calculated manually vs 22.0 on the computer. . .

car_fan

Current with my 7 fill-up, it is a differences of +/- 0.4 mpg between computer and manual estimation for a 07 GS350AWD (22-23.5 mpg in 7 tanks of gas).

kyang91

iTrader: (5)

I think mine is just a little bit off since I have a Tanabe Exhaust and a KN intake that will bring the MPG down a bit I think.

ecount00

just tracking the last 3 fillups have been .5 to .7 +/- from the computer. I'm not that confident in my unscientific method of filling the tank that i can say for sure the variance is even that much. Anyway, for my purposes, the computer is certainly accurate enough.