Indicated MPG vs calculate MPG

Poor Hyundai had to pay back customers for MPG claims that turned out to be false. My son received a $500 check from Hyundai for mileage compensation. Toyota better watch their fuel mileage claims because they are off more than claims made by the Korean company. So much so, that it's beyond fudging a little.

 

. Prius is rated 50 mpg and he got better so what are you saying?

 

Point taken. Speedometer sucks though

 

The dash mpg is maybe 1-2 mpg on the high side. Hand calculating is very hard because it is very difficult to put the same amount of gas in every time. Car only holds 11 gallons so if you don't fill exactly the same every time it will throw mileage numbers off.

 

Perhaps using a little math would be easier. miles driven (odometer readings)/gas for fill up = mpg

 

Exaggerating the displayed mpg and exaggerating the claimed mpg are two different things. Both frustrating, but it's the latter that leads to court challenges.

With about 120 fill ups with an overall positive error of around 7.5% (it varies, as high 9%, low as 5%) I'd agree with you. All I can think: Toyota is doing this intentionally, and pushed just as far as they figure credulity will swallow.

There's a few naysayers that argue "hey, it's the pumps, inaccuracy, and so on". But I don't think that washes: neutral inaccuracies would fall on either side; a consistent, relentless, positive bias is inexcusable.

 

I'm the complete opposite. My 2nd Prius stays consistently around 51 MPGs but by hand it's actually 58 MPGs going 351 miles on only 6 gallons.

Posted via the PriusChat mobile app.

 

^ That is strange.

 

Congratulations!
That means that you're measuring accurately.

 

It's easy to calculate your MPG:
Fill tank
Reset Trip Odometer

At next fillup:
Fill tank
Note gallons added
Note mileage on trip odo

Miles divided by gallons added = MPG

 

I posted this on another thread, regarding displayed MPG:

"There are numerous inaccuracies; for starters, many vehicles (including the Prius) report fuel consumption on the instrument panel display based on MAF sensor and oxygen sensor (A/F ratio) readings, not injector readings, even though injector readings correlate better with actual fuel used (although, even that is inaccurate--Toyota vehicles sum ten injector pulses per cylinder and then transmit that information to the ECU, which then averages it). A 2014 fleet study by HEM Data found an average 2.8% discrepancy between displayed and measured fuel economy."

That 2.8% discrepancy is among 4-, 6-, and 8-cylinder passenger cars from all manufacturers, BTW. Toyota isn't doing anything nefarious; it's just an artifact of how the information displayed is obtained, and it's endemic to nearly all cars with an MPG display.

 

Hyundai (and Kia?) got in trouble for reporting false EPA test figures. Do you have information suggesting Toyota also reported false EPA figures?

The MPG numbers displayed on the dashboard are not regulated by any federal standards, and are not used in any of the CAFE / EPA testing.

 

My display averages 2 MPG optimistic. It's important for me to know average MPG accurately since I tend to run the fuel tank very low. I multiply the average MPG by 10 (the PiP has about a 10.2 gallon usable capacity) to estimate my maximum range to a high degree of accuracy.

No and no. MPG ratings are supplied by the manufacturer and certified by no one.

The EPA tests about 10% of vehicles to keep the manufacturers worried. Apparently Hyundai wasn't worried enough.

 

Since the car has been new, the computer consistently reports 5% higher than reality no matter the MPG I'm getting or time of year. Based on the number of people with a similar experience with Gen3 Prii, it seems Toyota intentionally tuned it to the high side of acceptable.

 

The annoying thing about that is that range can easily be calculated in the PiP since the fuel tank is 10 gallons. You simply tack on a 0 to the cumulative MPG display, and that is your range. If the MPG shows 50, then your range is 500 miles. A 5% overestimate will have you running out of fuel 5% sooner than your calculated range.

I understand why Toyota would be optomistic with the MPG, but it can mess people up who rely on the accuracy.