2012 Prius Gas Mileage

So far after over 5,000 miles on trip A after
several fill ups the computer is off by
about 2.3 mpg over reading.

I keep accurate records so its not as bad over several tanks
I think some other car over read a lot more and some, of course,
under read.

With over 52 mpg in real world driving, the last tank was over 58 mpg
calculated I am not complaining. Its probably the best car we ever
purchased.

Before the Prius, my Honda 1994 Civic VX got great mpg's but not
like the prius and I don't have to shift anymore going up the mountain passes
and so much more power in the Prius.

I believe if 30 % of the driving public had a Prius millions of gallons
of gas would be saved.
The only issue with having a high mpg car is that you drive it a lot
more than other cars. We can go back and forth to Portland Oregon
for less than $15.00 and the money saved goes for a nice dinner.

 

OK no problem .. what almost three years data shows:

Your MFD reported mpg is biased 5-6% but seems consistent ... so if reall mpg drops you can see it there as well ...

In other words, you only interested this sort of "relative" changes, yes you can trust ... the MFD ...

Again, maybe I was unclear .. I was not at all complaining of "completely" accurate ... and if the user KNOW that it is just over reporting it could be just fine ...

For me saying that the measurement is 1% 2% or 5% accurate is just fine, but that should be some sort of probability distribution not biased as this.

But, again I do see your approach is somewhat different ... and we actually know that reported MPG is accurate but higher then real you can just use the number to see trends

 

With my particular car, I've only had it for 3 months and filled it 4 time. I don't including the tank it came with which I threw out because I didn't know if it was really full or when they reset the trip meter. So I have no way of knowing yet if there's that much of a difference between calculated and MFD. Two tanks were a bit over, and one was a bit under. In another 6 or 8 months I'll be able to discuss it with better data. My car may be different from yours. Or not.

In defense of Toyota engineers - because why not? - it must be terribly hard to program it accurately. It's a complicated system, and once a car leave the factory floor, Toyota has not control over any number of variables that could skew the results. If they tested it via simulator in the lab... all bets are off when it comes to real-world application.

 

I have found my computer to be about 5 percent optimistic. I don;t bother checking anymore.

 

What percentage does this represent?

 

If we assume 54.3 mpg (as he mentioned 52 mpg "real world" driving in his post), 2.3 mpg/54.3 mpg = ~4.2%. If we assume 2.3 mpg/52 mpg = 4.4%.

A lot of people don't bother to calculate their MPG, thus they see the read out and they are happy with the results. I'm not one of those people, I would like it to be more accurate that it currently shows.

There is a bias to the "optimistic" side. I have zero clue how they calculate the displayed mileage, but I suspect that if they took the final result and multiplied it by 0.95, they would be close enough to the calculated value that even the scientists and engineers would say that it is good enough.

I hate it when people get in my car and are amazed at my displayed MPG. I always feel compelled to tell them that it is optimistic and the real MPG is XX. I'd like to not have to do that.

 

Same here. 65mpg looks soooo much better than 62mpg. Or worse yet, 57mpg instead of 60mpg. Ugggg lol

 

"A lot of people don't bother to calculate their MPG, thus they see the read out and they are happy with the results. I'm not one of those people, I would like it to be more accurate that it currently shows."

Uh oh, jabecker is on this thread. She got hysterical when I mentioned calculating your miles is more accurate than the display on the Prius.
She see's no empirical proof that the car is not correct.

You better watch out! haha.​

​

 

I feel the same exact way. It's the engineer in me!!!

 

Yep, it is the scientist in me (and I'm in Quality, so I really DO care about accuracy AND precision....a lot!)

It's awful! My current MPG reading is 68.0 mpg. A group of us are going out to lunch today, if I drove and people saw it, I'd have to explain that it is optimistic and that I'm really getting ONLY 64.5 MPG or so. I'd rather they get in and see it state 65.0 MPG, (even though I knew it was 64.3 - 64.5 mpg), it would be close enough to not bother correcting.

The gauge isn't too accurate, but it does have a fair amount of precision, and I'd rather that the precision with a bias than accuracy with lousy precision.

 

I kind of agree until here...

Well I am engineer too ... I would say even a little less precision but no bias would be better. I am talking about random sampling error, with reasonable distribution. In general, YES any given measurement would be less precise but the long run over many samples we would be better off. But as someone else said we do not know how exactly toyota getting this number ... but since the positive bias seem to be constant and the same over very many car and driving style etc. I am convinced this is design (or rather design flaw). Another thing convinced me. After I adjusted my SGe for distance which was little off .. the mpg it calculates (again I do not know what data is used) is 1% on the money with my calculated mpg and the error up and down but just about 1 -1.5 mpg seem to be lower with higher average speed over the tank.

 

You just described the GenII. Individual tanks could be wildly off but when 20 tanks are measured the error was only about 2% vs. the 5%+ of the GenIII.

 

I realize that the display is off by a few percent, but it’s no different than the display was in my Chevy Cobalt. In both instances I just use it for relative tracking. Is my driving skill improving at achieving better fuel economy, or is the car's fuel consumption suddenly changing by a large amount, sort of thing. I have calculated a few tanks so I know what mileage I am actually getting. Yes as an engineer I would like it to be more accurate, but that’s life.

 

Yes I know I HAD a Gen II so this is another reason to beleive that toyota did this ON PURPOSE they got it right with the previous car dam it ....

 

I'm not given to hysterics about most things... certainly not over gas mileage calculations. With my car, I have too few data points to even compare.

Neither method is as accurate as the engineers in the thread would like it to be, because there are too many uncontrolled variables in each case. As I said above, I'm simply looking for trending. Either method works fine for that. I still bet that the majority of drivers don't check at all, and only look at their MPG because the Prius hands it to them.

 

Why do you feel compelled to tell them anything at all? Just smile and nod and say you really like your car.

 

Because as an engineer, if anyone ever questioned you on it, you would feel like a fool not coming clean in the first place. It's just the way we!!!

 

It's a curse anyone who is trained in science is afflicted with.

 

I'm trained in science, and I feel no such curse. If I'd built the system myself, I might feel compelled to. But, for me, it falls under "not my problem."

 

Because I feel compelled to make sure the facts are as accurate as reasonable. If someone were to get into my car and see the 68.5 mpg that is displayed they might tell others who might come up to me and say, "I hear you get 68+ mpg". That isn't a true statement and I don't like perpetuating untruths (just my personality....It's probably why I like www.Snopes.com so much)