2012 Prius Gas Mileage

We recently purchased a new 2012 Prius for the gas mileage. We checked our gas mileage the old fashion way, keep track of the mileage between fill ups and divide the mileage by the gallons per fill up. The computer in the car tells us we are getting 48.1 miles per gallon since new, but our records (the old way) show the following: 1st Tank: 39 miles per gallon, 2nd Tank: 44 miles per gallon, 3rd Tank: 47 miles per gallon, fourth Tank: 44 miles per gallon and the 5th tank: 42 miles per gallon. If any of you out there think you are getting the mileage the car's computer is telling you, you should check your mileage the old fashion way!

That's why there is fuelly.com! It measures your actual mileage vs gallons of gas. I know my CONS is about 5.5% too high. You will learn to drive it more efficiently as time goes by and you start honing your skills.

The computer reading is always anywhere from 2.2-3.1 mpg higher for me personally. I track all my mileage on Fuelly as well.

Welcome to the Toyota Prius optimistic MPG computer !!!

Subract about 2.2 MPG from what the computer screen says and you should be right on.


REV

You should use the search function and read the numerous threads on the subject.

A person who has one clock knows what time it is. A person who has two clocks is never sure.

a person who has a broken clock is right twice a day.

The person with three clocks is more sure than the man with two clocks.

Not if those clocks didn't take into account the leap second that was just added on June 30th!

About every one and a half years, one extra second is added to Universal Coordinated Time (UTC) and clocks around the world. This leap second accounts for the fact that the Earth's rotation around its own axis, which determines the length of a day, slows down over time while the atomic clocks we use to measure time tick away at almost the same speed over millions of years.
So, leap seconds are a means to adjust our clocks to the Earth's slowing rotation.

Only if two of them agree.

Damn you guys! lol

-2.2's the magic number for my Five too.
If we know this... why can't Toyota address it?

My 2012 seems to be off more than the 2011 I had. 2011 was anywhere from 2.2 to 2.8 higher. My 2012 have a more narrow range of 2.9-3.1. higher.
When I get gas I never top off and always stop at the first click. I go to the same gas station each time.

You shouldn't be stating the difference of how many MPGs you are off, you should be stating the % difference. If you are 3 MPGs off and the display says 50 mpg vs 60 mpg, then that's a difference of 6% vs 5%. At least include both mpg difference and % difference.

For instance over my last four fill-ups:

3.075 mpg difference which is a 5.5 % difference

My lifetime (50,000 + miles) shows a difference of 5.7% (3.4 mpg difference [63.2 mpg displayed and 59.8 mpg calculated]). There is a sticked thread for this.

A person with just one clock has no measure of its probable error.

And doesn't care, because in non-scientific applications, it's "good enough."

You can research this further, but this is a real issue since 2010 ... the FC (mpg) calculation of the car is BIASED about 5-6% positive ..... there are many many thread about this I am close to 40K NOT ONCE computer showed less then I calculated closest was 2.9% ...

Your calculation is probably have a randomized 1.5-2.5% error rate but again randomized on a tank by tank level. If you are more interested overall MPG your calculation will be very very accurate (more so overtime) not counting tire ware which may introduce some biased error as tire wares out but that is no more then 1% max 2% if you go for "slick" surface ...

many were hoping that Toyota will fix this for the 2012 ... but NO...

Real weird thing is that I had a Gen II where there were error btw MFD/computer and calculated mpg, but it was random which is expected. And if I kept TripB for 10/20 tanks ... my overall calculation and the MFD agreed within 1%

I am not sure what you mean ... the issue here, for me at least as an engineer, is the BIASED error not the error or the probablity/distribution..

I found this amazing that toyota's engineer or managment let this fly ... for what ever reason .. this should have been absolutely visible from just base testing ..... and again error by itself is NOT the issue but when you see biased error, that should be a big red flag for any serious engineering team (engineering is scientific by definition)

I am guessing this was a marketing deceision ... which was really stupid because Gen III was beating easily Gen II for me more the 10% on careless driving 15% at least driving for mpg...

I realize that not everyone thinks the way I do. What I meant was, that for me at least, the exact to-the-nth-degree MPG is not that important. What I'm looking for are general trends: does it go up in spring and fall and down in summer and winter? Does it get better as my tires break in? What happens on a long trip vs more in town driving? That kind of information is interesting because it allows me to spot an odd drop or gain in MPG that I might want to explore to see if I can figure it out. A drop could be something like the 12v about to die.

There are so many uncontrolled variables with both methods that the probability that either is completely accurate is fairly small. So for most people, just picking one and using it is sufficient for the kind of trending that I mentioned above.

Many people I know who aren't Prius owners ignore their mileage. The tank gets empty, they fill it up.