How much fuel left?

Mine had estimated 52.?, so it was actually 4 over what I got.

 

I've noticed this as well. I use the app "Calcbot" on my iPhone just for mileage calculations, and when I look back at the "tape" from past calculations & compare it to what my car dash tells me, it's +/- about 2.2MPG.

 

Mine was only about two over on the second fill-up. I wondered if it would eventually become pretty accurate...I guess not. Though two over is easy enough to calculate.

 

I don't think it's possible for Toyota to make the the mpg displayed accurate. Honda can and does, but that's about the only nice thing I can say about their hybrid vehicles, these days.

 

Why can Honda do it and not Toyota?

 

If u use a ScanGauge2 ... u can get amount of fuel used, instant and average mpg readings, temp.,small battery volts, and etc. Very useful

 

It seems like everyone's reported mpg overshoots by a fairly constant average of ~2 mpg, so subtract 2 (or some percentage).
At the very least, they could provide a calibration setting.

 

Basically, I don't think Toyota's capable of resisting the urge to BS on mpg.

With our previous Civic Hybrid, what the dash said for mpg was invariably spot-on or slightly pessimistic, ie: calculated was the same or better. Of course the Prius, at least around town, does 10 to 20 % better (calculated vs calculated mpg), but that's another story.

 

Then Toyota should lie on their EPA estimates like Ford does. No, wait, only Ford gets away with that BS

Yeah, I think +2 is maybe about right.

 

I have no reason to not trust the computer's displayed MPG (or at least no reason to trust it less than my own calculations). The car's computer knows how long it is telling each fuel injector to remain open (pulse width) and, unless there is a problem, the fuel pressure supplied to the injector is constant. At X fuel pressure and Y milliseconds pulse width, you will get Z amount of fuel injected into the engine for the purpose of moving the car... Every time. The computer knows all of these variables. The computer also knows distance traveled. It's an easy calculation. Of course there is a margin of error in this situation. I would argue though that the margin of error is much larger when I try to calculate MPG's myself as each variable (slope on which car is parked, temperature of existing and new fuel in the tank, fuel station/specific pump used, my calculation method (significant figures), when I think the tank is 'full,' and how many times I have repeated the experiment (very important) of pumping fuel and calculating it against how many miles I have driven to arrive at MPG) in this situation is subject to much greater variability.

I'm not arguing that self-calculation of MPG's is a bad method or can't result in an accurate (useful) figure, rather it is a terrible way to question the integrity of the MPG's that the car displays. When I self-calculate, I take those results with a grain of salt.

 

Just because your sample MPG checks have a large margin of error, doesn't mean all our longterm MPG monitoring has a similarly large error margin.

For those of us who keep continuous fuel logs for the life of our vehicles, many of the variables you mention cancel out or shrink to being negligible compared to the car's display bias that we discover.

Retail fuel pump accuracy is regulated by law, and becomes actionable when found to exceed a certain level. Odometer accuracy is indirectly regulated by the tort lawyers (I have received class action settlement notices for two past cars of other brands, though my particular cars did not have the error magnitude claimed in the suits), and can be checked and accounted for by the user. My Toyota odometers have been quite accurate, with a very small error in the opposite direction from the observed MPG display error.

Reagan said 'Trust but Verify'. Many of us have done the work to verify the display MPG, and have found plenty of reason to not trust it.

 

I agree. Repeated measures with reliable results do reduce margins of error. That's why I said that was very important. Another thing to consider here is the difference between reliability and validity of results. Sure one could have reliable results every time they fill up their car and perform the calculation, but are they valid? The validity is where my concern lies.

It's the method of verification I am worried about. I'm not saying i'm not skeptical of the trip computer's MPG's. I just feel uncomfortable making such claims challenging the validity of the trip computer's MPG using such crude, uncontrolled methods (just my opinion, although you do bring up good points of debate to counter my opinion). As much as I may be skeptical of the trip computer, I am similarly skeptical of such 'fill up and calculate' methodologies for the purposes of making such a comparison(especially if this is my only data source). I just think the methods lead to results with low and varying validity. I don't trust the claims based on this methodology and they wouldn't hold weight in any type of academic or scientific debate.

 

We don't need our tests to hold up to a refereed academic journal when automotive MPG displays are not held to that standard, or even to any standard whatsovever.

 

I know the old saying in boats was "MY boat went a lot faster before I bought a GPS"

LOL

 

Oh spare me.

No matter how much info the car's computer has it's disposal, the final step in it's calculation is to inflate the value, as evidenced by the consistent positive bias vs calculated. My 2 cents, this is very likely intentional, a request from Toyota management.

If you know how much fuel you put in, and how far you went, you can make a very accurate calculation of your mpg (or liters/100 km, north of 49). And, any inaccuracies in a single tank cancel out over two or more tanks.

 

Sorry. Maybe I am putting too much thought into it.

 

I'm getting uppity. Sorry too

 

I was thinking the opposite. Too much faith in the honesty of the car makers, on a valuable boasting item that is completely unregulated. And not enough thought into how drivers can make reasonable measurements of this themselves. The later is not rocket science, at least to an accuracy useful for most of us. And many of us are in engineering and technical careers where test and measurement are core portions of the field.