Huge variance between computed mpg and MFD

[DaveinOlyWA]

<div class='quotetop'>QUOTE(Jeannie @ Jul 5 2006, 01:02 AM) [snapback]281308[/snapback]</div>

I've had my car a little less than 3 months and just passed the 2000 mile mark. My "computed" mileage is usually about 2 MPG less than the MFD. I live in New Jersey where we don't pump our own gas, and so far I've filled up at different stations. So I know that the computed MPG depends on how much the tank is filled. One fill up gave me a computed MPG 2 miles HIGHER than my MFD! So I keep my 'computed' numbers in an EXCEL spreadsheet where it computes single-tank MPG, cumulative MPG, 2 tank MPG, 3 tank MPG, etc. [/b]

Jennie, what you are seeing is perfectly normal. i also have a spreadsheet for mileage and actually have 4 different sheets with a combined info sheet (bit unwieldy). i track summer and winter mileage separately.

also have another sheet for "temps" tracking. i have a relatively consistant commute to work which is 7.5 miles. all at 35 mph. this is just barely enough time to warm up the car (usually its warm about 50-60% into the trip on cold winter days). this makes the data perfect for comparing mileage verses OAT. seeing my average on this trip being 35-50 mpg in the winter and 55-70 mpg in the summer made me realize that the higher the temps, the better the mileage.

moral: take advantage of the additional data your car provides for you. more importantly, this data can be an early warning indicator of developing problems. besides, having data on paper is great ammunition of naysayers around the water cooler when you are building up your Prius