Which MPG is right?

There are quite a few existing discussions on this. You'll get many different ideas about it around here. It's pretty consistent in the error and always shows higher than actual MPG. It probably has to do with the inherent error in the odometer. I usually see it about 2MPG above the actual.

BTW, if you reset the trip history display on that info screen, you also reset the average MPG displayed on your dash when on ODO mode.

 

Correct, never go to the history screen if you want to keep that "lifetime" mileage.

My v can be 5% optomistic, my last tank claimed.44.1 MPG while fuelly.com claimed 41.9

 

To directly answer your question: your calculation is right, what the car's telling you is an exaggeration.

I believe with the v and c, and maybe the later model regular Prius as well, the exaggeration is diminishing. I can attest with our 2010, and I've calculated mileage virtually from day one, the average error is 8%.

I reset Trip A at each fill up, but basically just for feedback, and I know if it's saying 4.5 (for example), reality is going to be around 4.9. Also, just for safety, I use the odometer reading for each calc, verifying against the trip meter: the trip meter is good for (inflated) feedback, but can be accidentally reset.

 

I've brought this up before, and have taken it as a long time project to research, but there ought to be a way to tone down the optimism of the car's estimate. This isn't error, it is bias. I can understand why they do it - the vast majority of their customers will just accept it and it makes them feel better. But for those who have the interest to do so, having OBDII devices, etc., there ought to be a way to actually calibrate the thing. Heck, the feature I'd like is to just be able to type in the quantity of gas you put in and let it slowly, very slowly, adjust itself. If not that, then being able to change whatever coefficient is used to divide gas consumed by distance traveled. It could even be a advanced setting with a +/- 10 point scale, with the endpoints being, say 5% of adjustment. Heck, my dSLR lets me do that individually for my lenses' focus distance. Why can't I do this for the most important feature readout of my car?

 

What odometer error? There shouldn't be any significant 'optimistic' odometer error, especially in this era. If you find one, contact the product liability lawyers who shook down Honda, Subaru, Kawasaki, and maybe others, for 'warranty fraud'.

My Prii (not your 'v' model) have odometers reading 0.2 to 0.3% pessimistic. My past Honda and Subaru were covered under the above class action settlements, even though my cars didn't display the purported 'defect'. The lawyers were paid well, the lead plaintiffs got some money, the rest of us got 2% warranty extensions. Whoop-te-do, my cars were long long past warranty and still trouble-free at that time.

Probably because of that lawsuit, my current Subaru odometer reads about 1.8% pessimistic.

The MPG display error is from a separate bias.

 

How I learn is to watch my instantaneous mileage display (doing it safely) and learn what actions and speeds and terrain affect my mileage. For example watch what attempting to maintain your speed even up a slight grade can do to the MPG. From watching it drop as you go up a hill, you learn that for better MPG you try not to accelerate up hills and even lose a bit of speed if traffic permits.

Fuel pumps contain their own errors so even though they print out to the .000 place, I ignore the individual fillings as the pump shut-off can be different from pump to pump. I figure only over many fill-ups will the figures become more accurate.

 

Or just take pleasure in the better mileage number with the same joy as a plump housewife with a bathroom scale that consistently reads 15 pounds too low...

 

My display mileage has gone from around 45 mpg to about 39 since the summer months. I don't think it is just an error, because I am getting less miles between fill-ups also. I took it to the dealer and they took it on a test drive with a laptop hooked up and said it got about 52 mpg. I really don't believe it is getting any where near that. Why would their test show such a difference? And, more importantly, why is the car getting less mpg now than it was previously?

I just noticed that this is for the V. I have a standard 2012 Prius.

 

This has been discussed at great length in MANY threads on here already.
The battery is less efficient when the temp. is HOT.
The ICE is a little less efficient too.
The gas formulation likely is different in the summer.
The AC uses more energy than the heater does.
People may even drive more aggressively when it's hot.
It all ads up.

 

There are failure modes for the 12 volt battery where the Inverter constantly tries to recharge it. Some morning test the 12 volt battery before you start the car. It should be over 12.5 volts

If it is below that, it may be hurting MPG.

 

There's a clue. Are you using AC? Kind of rhetorical question considering your location? Even if you're using it year 'round, it's likely used more, and harder, in summer.

What temp are you running the AC at? If you're hitting Auto and with temp set low, the fan's going to race, put max load on the system, Try setting overriding mode to High/Low (air directed at face and feet) and raise temperature enough that the fan is not going full tilt. As the interior climate stabilizes, try to settle in around 75~76F. Also, maybe avoid AC use in short trips where it's kind of a lost cause anyway, just roll down the windows, pretend it's the '50's.

 

Little road trip. 220 miles from Vermont to Mass, North Shore. Interstate the whole way, 70 mph to 75 mph, the entire way. Upon arrival, I was at 45.5 on the display. We've driven another 150 miles since, slow city, fast highway, suburbanish. The display reads 46.8 mph now. I'll update when I fill up soon, be an interesting tank to measure.

AC all the way, dry weekend so I set the temp at 73-74 F. Never use auto, it's annoying as all heck, and not very even.

 

Drove my v 420 miles on Friday, to Lousiana. It's hot down here! It was about a 50/50 mix of 55mph 2 lane highway and 70/75mph interstate. I am not one for pushing the fuel gauge too hard, but did this time. Low fuel light came on 10 miles short of my exit, 15 miles short of the fuel station I wanted to use. So I switched to the display mode that showed miles left. Got to the gas station with one bar still on the fuel gauge, 4 miles left on the range display and took 10.009 gallons. So I still had almost 2 gallons left, in reality.

Worst mileage I've seen out of this car, at 42mpg. But it was the first extended trip and with this much interstate. I was semi-aggressive on the 2 lane, driving mostly 60-61 and passing where needed. Locked down 71 on the CC on the interstate stretches. Still, a whole lot better than the 23mpg I would see with my WRX on this trip, and that was burning premium fuel also. The "fun" factor on the WRX was much higher on these twisty, Ozark Mt roads, for sure. But overall, I'm very happy with this car so far.

 

I couldn't fill up before driving more miles, mostly upgrade highway speeds. So my big trip ended at 400 miles with a fillup of 8.8 gallons. Calculated was 45.45 and displayed was 45.5. Closest yet. Interestingly enough, from there home, with more weight added, more uphill, and higher speeds, I arrived home with a displayed mileage of 42.

Almost all highway speeds, AC on the entire trip.

 

I'm new to a hybrid entirely and in two weeks I'm falling head over heals for mine...coming from a Tacoma to this is a change, especially in fuel economy. Can anyone say how long it takes for the "V" to be broken in to get the better fuel economy? Is it different for a hybrid?

 

There is a minor break in for the tires, and again when you need new tires, but it usually takes about 15,000 km to train the driver.

I think you are doing better than me already (5.8 l/100km for me) but yours may be all summer driving.

Toyota Prius V Mileage | Fuelly

Due to insane naming by Toyota, some error will be because a 2012 and newer Prius v and a pre 2011 Prius V are not the same car, confusing the inattentive.

 

Question: Had my 2013 Prius 4 about a month. I reset A trip odometer each trip. Average 55-65 on my commute. But the A odometer is usually a bit higher than the end-of-trip stats that show after car is turned off. Any reason? (For example, Trip A shows 59.2 mpg while end-of-trip status shows 60.2.)

 

You'll find more specific info in the Gen-3 forum. However, the ODO reading is based on the mileage since you last reset the history data. The Trip reading is specific to that trip meter.