Inaccurate MPG?

Always have.
Always will.

My (work car) 2010 always favors the house by 5-10 percent.
I don't fret about it much since I always hand calculate at the pump and determine my real world MPG tank by tank, rather than trip by trip.

I'm not sure if the G4s have this same bias, but Priuses are somewhat infamous for having 'fake efficiency' displays.

AS ALWAYS.......
YMMV

 

With liters per 100 kilometer system, lower numbers are better. As @ETC(SS) says, always in favour of the house:

 

you need more data. it doesn't fill up the same each time. sometimes i get more, sometimes less, sometimes right on.

 

I've always seen the car report around 5-7% less fuel usage than it's actually consumed as measured by litres pumped. But that's based on many data points - the individual points vary because you can't rely on the gas pump's auto-shutoff to always fill the tank to exactly the same level. I've seen numbers ranging from as far as 2% pessimistic (car reports more than actual fuel consumption) to 11% optimistic (car reports less than actual fuel consumption). But those outliers are unusual - almost all my fill-ups are in the 4 to 8% optimistic range.

Of course it's entirely possible that the algorithm has been changed in the 2016 Prius C, so it will be interesting to see what your experience will be like be over several fill-ups.

 

This.
Mine has always calculated lower than the display no matter how I do it. So does my Fusion.

I think it is probably more accurate if you fill to the second click, using a reduced flow rate after the first auto-stop.

 

The more fillups you do, the less pump vagaries come into play. Even by two or three fillups, the accuracy is getting really good: if your pump shuts off a bit early one time, it balances out on the next. Our third gen: a tediously regular 7.5% bias. The Toyota BS factor...

 

Like everyone else, my 2013's displayed MPG runs about 6% higher than calculated at the pump. I have never experienced a tank where the display was lower than the calculated MPG (my data is here).

It will be interesting to see what happens as you gather more data.

 

Please update your report when you have about 10,000 miles of data on this.

 

Yes I have the data for every fill on our Prius. Before that I was out of the habit for about 20 years.
Of course Gen2 has the infamous Guess Tank.

I actually don't even record the Prius number on the MFD.

 

I do, but just because I don't want to "break the chain" in my spreadsheet.

 

FWIW, I used to drive a 2012 Toyota Prius-c Two, which I had almost 50K miles on it and 111 fillups. The MPG, hand-calculated, was almost always 7-8% higher than what was being reported by the car's MFD. I now have a 2016 Toyota Prius-c Two, and have over 10K miles on it now...24 fillups to date. I now get the opposite results where the MPG, when hand-calculated, is about 4% lower than what is being reported by the car's MFD. I always tried to fill up about a gallon past the first click-off point to get more accurate tanks, though sometimes I 'top off' a bit less if I saw the gas reaching the top of the filler tube. I just rely on the hand-calculated results anyway, so not too worried about the discrepancy...I got 56 MPG in my 2012 Prius-c and currently get 54 MPG in my 2016.

 

Not unless you go to the same pump at the same station all the time.
Fuel splashes around as it goes in at a fast rate......and the auto-shutoff will trip prematurely sometimes.
Going to the second "click" is better but a long term average is best; like at least 5 fillups.

 

As long as you use the same fill technique each time, your calculations will be fairly accurate, and again: any vagaries in a single tank calculation will balance out in the next tank. Or two fillups, at the most. Pumping gas up to the neck is a fools game, can mess up the gas fume control system (expensive), and just ticks off the next guy in line.

My 2 cents: fill till it shuts off, done.

 

Nobody in this thread suggested that you do anything like that.

If the nozzle is still fully inserted, going to the second "click" will NOT cause an overfill condition.

 

Actually, MoarMPGplz claimed to do exactly that, so I think the caution about messing up the evaporative emission control system is well warranted.

 

OOPS. Sorry I failed to read to the end of his post.
You are right.....HE is dead wrong......this practice is not only dangerous because of potential spills but it can result in an expensive repair bill......AND it accomplishes exactly NOTHING useful.