MPG... Just mentally reduce what's displayed by 10%?

Maybe on the left hand side of the pond, but not in UK AFAIK. London may have that facility tho!

 

Your owner's Manual (USA) states:

 

Yeah 7.5% is the number on my 3rd gen. That's total gas and kms tallied over 6 years, pretty much since new.

 

In a previous post (#25) you said you were getting 7%, how has that now changed to 5% ?
In the UK the pump stops when the breather in the nozzle gets blocked by fuel, the filler pipe exit on the pump is high up, so nothing is siphoned back into the pump and theoretically if you lift the filler hose the petrol should drain into your tank through gravity, although I'm not sure if this happens in reality as I don't do it for fear of over filling and ruining the charcoal vapour evaporation canister.
In practical terms it doesn't make any difference if you stop at the first click or the second, as long as you do the same every time to get the same level of fuel in the tank so you know how much you've used.

 

Summer time I guess. For the past few months I've stopped caring about getting the best mpg so I've been driving quite a bit faster. My mpgs have dropped. And I've also seen the difference in mpg drop as well. My last tank was extreme for example had 2 mpg difference 58 calculated, 60 displayed. Maybe the car is learning with mileage. I'm not sure.

Perhaps the clicks dont make a difference. I don't know. It's just what the article wrote. Maybe this needs engineering proof.

 

My first tank experience is the same. 2 MPG difference between what the Prius says and what I calculated after pumping. I wonder if Toyota engineers allow up to the 5% difference as a margin of error.

 

A statistician would be less kind: there's only one plausible explanation for an error that's regularly in favour of "the house", and yet in a fairly tight pattern. And I really doubt the engineers determine this.

 

l am actually quite impressed with my 2017 Prius 4. I had been more or less accepting the displayed MPG of about 60-64 MPG and thinking what a great deal that was. But after reading this forum I got suspicious and did my own calc at the last fill-up. The displayed MPG was 63.2. I had driven 339.7 miles and needed 5.422 gallons for the fill-up, which comes out to 62.65. Awfully close to the displayed value - just off by 0.8%. I will check this over time as I know this stuff can change, but at 4 months old, the car is everything I could have hoped for.

 

I've had my 2016 Prius Eco for just over 7 months. Almost all my driving has been in the city, although that includes some interstate ( 58- 60 MPH) driving. At my last fill up I was getting right at 72.5 MPG after having driven 9,000 miles. Say, that's better mileage than I,m getting with my 2000 Crown Vic. I am due to take a trip to New England soon. Let's see what that does to my MPG.

 

Same here. I’ve had my 2016 for a few thousand miles and have found it is also consistently 7.5% more optimistic than real world MPG figures. I really wish there was an option to adjust the calculation in a submenu to account for this error.

 

I'd describe it as an intentional "error" on Toyota's part. There's no other way to look at it: it's a consistant bias, goes up and down a bit, maybe partly due to the vagaries of the fill up process, but on average very consistent, and way off on the positive side.

 

Someone go to a pump you have used multiple times to calculate MPG and fill one or two large portable fuel canisters and compare the reported pumped gallons to a more carefully measured amount. It's possible, but unlikely, that all of the pumps are off. I wonder if there are regulations that allow a 5% or so pump "error".

 

That much meter error is seriously illegal in the U.S. and would cause inspectors to shut down the pump. But "weights and measures" enforcement is much too infrequent, any given pump may not be inspected for years at a time.

I'm not quickly finding good references, but one source hints at allowed error rates in the 0.25% to 0.5% range.

 

Spreadsheets aren't too hard.

That said, I don't think that it's something particular to the Prius. At first, I wondered how the Prius could be overshooting its MPG by as much as it does, compared to my manual calculation, but then I realized that's only if I looked at absolute MPG numbers. By percent, in my experience, previous non-hybrid cars have been off by about the same amount.

EDIT: aaaand I just realized the dates here, and I've kind of necro'd a thread, sorry!

 

With all the variables that can impact mileage, 5-6% isn't worth quibbling about. My 2010 over the course of 315k miles I had it, was 6% optimistic on mileage and 2mph high on speed. So is my 2017 (212k miles). I don't even hand-check mileage anymore - I just look for big changes tank-to-tank that I can't account for (weather, how much I run the heater, changes in trip profile).

I've come to the conclusion that Toyota just wants to keep me from getting a speeding ticket, and feel all smug about how much fuel I'm not using (why else the $/tank saved function?).