Which MPG is right?

Thanks for the reply JimboPalmer. I feel like I am being trained...and yes, so far it's been summer driving. I have a few other seasons to look forward to to continue to monitor my fuel economy, and with winter approaching, I'll be checking for tips on winter tires and such too.

I'm quite pleased so far on the whole hybrid lifestyle, and having found this group to get tips/help from.

 

So it got cold early this year. With colder days, my first display reading was 38.9, actual calculated was 36.84. Second tank with snow tires on, indicated 38.3, actual fillip was 35.22. I noticed this last winter as well, the calculated mpg starts to leave a wider gap from the display mileage. Is this due to the different volume measurements of cold versus warm fluids?

 

Could be a lot of things. For starters: for me the error between dash and calculated varies from 5 to 9 %. For various reasons, fill inaccuracies not the least.

 

Agreed - fill-up inaccuracies account for more difference than the disparity between computed and actual MPG. Enough so that single tank calculations are not to be relied on. 5 to 10-tank average is far more reliable.

 

You didn't show your work, but I presume that hand calculated values are correct.
My work Prius (2010 G3-Two) has a similar MDF issue, and in fact I've been reading posts about this for 5 years now, so I presume that it's not an uncommon condition.

As far as explaining the diffeerence???
Let's just say that the bias always favors the house.
I'll let you figure out why.....

 

But a 50% disparity in the difference between displayed and calculated, when it's cold. Grated 1-2 mpg increase, but still. No question I fill more now based on the fuel gauge itself.