Lifetime MPG

Lifetime MPG is an interesting topic. It becomes basically uninformative after about 10,000 miles of data. Rounding goes from being annoying to an actual inaccuracy...

In other words, there isn't one. On-Paper is the only true recording method.

 

zzz

 

Here is the speadsheet I used. It was made for tracking or two Prius. It tracks lifetime MPG, but I also seemed to notice what John talks about after 10k miles so I also have it track the monthly and yearly MPG. It is a compilation of many people's logs here sorry do not remember who. If you can think of any improvements please post it.

 

Starting with the beginning of year #2 for me, here's my Lifetime MPG calculated at each fill up:

49.4, 49.4, 49.5, 49.4, 49.4, 49.3, 49.2, 49.1, 49.1, 49.0, 48.9, 48.8, 48.7, 48.6, 48.6, 48.6, 48.5, 48.4, 48.4, 48.4, 48.3, 48.4, 48.4, 48.4, 48.4, 48.4, 48.4, 48.4, 48.4, 48.4, 48.4, 48.5, 48.6, 48.6, 48.7, 48.8, 48.8, 48.9, 48.9, 48.9, 49.0, 49.0, 49.0, 49.2, 49.2, 49.2, 49.2, 49.2, 49.2, 49.3, 49.3, 49.3, 49.3, 49.3, 49.2, 49.1, 49.1, 49.0, 49.0, 49.0, 48.9, 48.9, 48.9, 48.8, 48.8, 48.7, 48.7, 48.7, 48.6, 48.6, 48.6, 48.6, 48.6, 48.5, 48.5, 48.5, 48.5, 48.5, 48.5, 48.5, 48.5, 48.5, 48.5, 48.5

Notice how the range is limited to a only 1.2 MPG. With a flucuation so small, taking a month or more to change just one-tenth, seeing it would be rather boring.

Then when you realize that the margin-of-error between display and calculated is actually 1.3 MPG, the value of seeing it basically becomes worthless.

 

wow, mine and my wife's are all over the place, ranging from 45 to 65. I tend to do a lot of road trips and her MPG varies with required errands. The nice thing about tracking your MPG is that if you notice a sudden drop with no explained change in style, terrain, etc then you can check your car out. For me that meant check tire pressure. On my old car it meant tune up or maybe something else was wrong.

 

<div class='quotetop'>QUOTE(Tadashi @ Jun 18 2006, 11:56 AM) [snapback]273083[/snapback]</div>

My per-tank values vary from 40 to 55 throughout the year, but not lifetime.

Once you collect enough data, you'll see a stablized lifetime value too... even with the extreme conditions of winter and carrying bikes on the outside while flying down the highway with the A/C on.

 

<div class='quotetop'>QUOTE(john1701a @ Jun 18 2006, 07:50 PM) [snapback]273206[/snapback]</div>

I've started a spreadsheet (based on ones I've used on previous vehicles), and I've gotten (as of filling up this evening) 51.06 mpg since 1 April 2006. The most accurate cumulative (lifetime) calculation is to divide the total miles you've driven with the number of gallons you've put in. Period. I also ignored the first tankful since I didn't know if it was full. If you have intermediate tanks that you suspect are not ful, note it in your log, but the overall average will still be accurate since you will compensate by putting more gas in the next time. Ignore the MFD for lifetime calculations, though it is useful for trips and single tanks.

 

I fixed and added some stuff to the speadsheet I posted before. I noticed the lifetime fuel track was not working in the graph. Not that it matters much since it does not move much like John pointed out. I added a CO2 meter also. Basically, it calculates the amount of CO2 (19.56 lbs per gal of unleaded) you produce and you can enter the amount you saved based on your old car's fuel economy.

Erik, the sheet will calculate your MPG for the lifetime, year, and month. Also, it takes into account the first tank. When I got my Prius I only had about 7/10 of a tank but was too lazy to go back to the dealer. It would have been only about $5 of gas.

8/23/2006 - I have changed the expense tracker to allow the summary to show the latest service as well as be able to track expenses by catergory. I also added an emmisions summary page that includes the other pollutants (CO2, CO, NO, Soot, and Hydrocarbons).

8/25/2006 - I added the CY07-CY12 to the sheet. You can swap the Salsa or Driftwood names with whatever you use to differentiate your two vehicles.

9/29/2006 - I added a monthly mileage pages. I was just curious if I drove more in certain months. Also, added the yearly MPG to the gas calc page (I was curious as to not only how my lifetime change dwith the last fillup but if I affected that year's MPG). I have noticed I am getting better MPG the second year (either by better driving or engine breaking in). Also minor link fixed and formula corrections.

Since the uploads are broken - http://tadashi.priuschat.com/fuel_economy.zip