First Fill-Up Blues :-(

[tljax]

Bought my "New" 2004 Silver package #9 w/32000 miles after much research and lurking here. Drove about 60 miles before topping off the full tank. I reset all odo's and mfd and set off. Using the driving tips learned here and 70 deg temps. I was pleased with the 54 mpg indicated on the MFD. I was suprised that I was down to 1 bar at 371 miles, but knew about the gas tank bladder.. Ok. I Fill up 8.75 Gallons and get a calculated mileage of 42.3 I've read that the MFD can be off by a few miles, but 12 mpg! Mostly under 65mph with a few nice flat 2mile stretches to glide.. Any thought?

[darelldd]

<div class='quotetop'>QUOTE(tljax @ Apr 4 2006, 01:56 PM) [snapback]234897[/snapback]</div>

Bought my "New" 2004 Silver package #9 w/32000 miles after much research and lurking here. Drove about 60 miles before topping off the full tank. I reset all odo's and mfd and set off. Using the driving tips learned here and 70 deg temps. I was pleased with the 54 mpg indicated on the MFD. I was suprised that I was down to 1 bar at 371 miles, but knew about the gas tank bladder.. Ok. I Fill up 8.75 Gallons and get a calculated mileage of 42.3 I've read that the MFD can be off by a few miles, but 12 mpg! Mostly under 65mph with a few nice flat 2mile stretches to glide.. Any thought? [/b]

Believe the MFD calculation at this point. You cannot get an accurate "fill" mpg with just one tank. You have no idea just how much gas you started with in your first "fillup." Just like you don't know how full you got it the second time. Don't let it bug you - just listen to the MFD until you have a few thousand miles of numbers to play with. Be happy.

[tljax]

<div class='quotetop'>QUOTE(darelldd @ Apr 4 2006, 05:30 PM) [snapback]234912[/snapback]</div>

Believe the MFD calculation at this point. You cannot get an accurate "fill" mpg with just one tank. You have no idea just how much gas you started with in your first "fillup." Just like you don't know how full you got it the second time. Don't let it bug you - just listen to the MFD until you have a few thousand miles of numbers to play with. Be happy.
[/b]

Thanks for the reply!! I am breathing again, and will keep reading. Thanks for the great board!!

[vikingrob]

<div class='quotetop'>QUOTE(tljax @ Apr 4 2006, 04:46 PM) [snapback]234922[/snapback]</div>

Thanks for the reply!! I am breathing again, and will keep reading. Thanks for the great board!!
[/b]

And I'll be more than happy to provide a spreadsheet for the purpose (disregard the CO2 numbers, they are for diesel).

[Betelgeuse]

<div class='quotetop'>QUOTE(darelldd @ Apr 4 2006, 05:30 PM) [snapback]234912[/snapback]</div>

Believe the MFD calculation at this point. You cannot get an accurate "fill" mpg with just one tank. You have no idea just how much gas you started with in your first "fillup." Just like you don't know how full you got it the second time. Don't let it bug you - just listen to the MFD until you have a few thousand miles of numbers to play with. Be happy.
[/b]

I actually had a very similar first reaction (and I still think you're probably right), but the difference in MPG made me a little uneasy. I mean, the difference between the two numbers implies a 2 GALLON difference between one fill-up and the next fill-up on the same car.

Now, this is only one data point and I wouldn't be surprised if the first fill-up was a "fluke" (or if the pump had some problem with it), but I guess I was just surprised that there could be such variation for the same car at the same time of year.

[Tideland Prius]

I'm gonna assume my bladder's expanding. I'm not sure if it's due to the warmer temperatures or if it's expanding because of use. The last few tanks, the MFD gave me good numbers (49-51mpg) but the actual calculation is closer to 47mpg. However, I've been getting extended driving range so I'm certain I'm actually pumping more fuel in the tank.