[ehurtley]

Well, I just filled up for the third time, and by my math, I've gotten a lifetime mileage of 46mpg. (First tank 393 miles, 9.552 gallons, second tank 426 miles, 9.287 gallons, third tank 466 miles, 9.188 gallons.) The first tank, my math did not match the MFD's reading (I'm assuming the dealer didn't give me a completely full tank.) The second tank was within .1mpg, and the third tank is off by almost 1mpg. (Odd, the attendant topped off quite a bit more than the previous two, who just let it go to cut-off, yet my math is HIGHER than the MFD. Putting in more gallons should make my calculated amount lower, not higher.)

So I'm now having my avatar reflect my lifetime average. (Updated daily when I work, and when I feel like it when I don't work.) Now I'll make a web page that displays my current spreadsheet. When I get it finished, it will reside at http://www.hurtley.org/prius.html (I don't expect that link to work for at least a week.)

 

[Daniel]

Thanks, Ed, you made me feel good. My short commute keeps my mpg low, and I know it would be much better if I had to drive farther, but these days I'm at 46 mpg on the MFD, too. (My lifetime MPG includes winter, and does not bear calculating.) My consolation for the "low" mileage is that I'm actually burning much less gas than folks who drive farther.

 

[AgentElrond]

My "lifetime" mpg started low also (first tank 38.5 - ack!), but has been increasing slowly since then to where it is now (44.8 ). Part of the issue may have been my not increasing tire pressure until after the 3rd tank, combined with overfilled oil. :?

Note: I consider my own lifetime mpg calc (44.8 ) to be more precise than the database (45.3) as mine is based on distance to one decimal and fuel to three decimal places.

 

[SLowen]

You may want to try a couple of tanks of 89 octane gas. Although others on this forum say it makes no difference, on my car it gets between 4 and 5 mpg higher on 89. If you do the math, it is still a better deal taking the 45 mpg for 10 cents/gal, but I like to see the high mileage on MFD and the car seems a little more responsive with the 89.

 

[ehurtley]

You fill to within 1 teaspoon of the same 'fullness'?

Fuel to three decimal places only matters if you are filling it to the EXACT SAME POINT in the gas tank, to three decimal places. It's a case of precision vs. accuracy. You are being very precise, but there's no way to be sure how accurate you are. 0.001 gallons is approximately three quarters of a teaspoon. Do you really think you fill your tank to the same point every time, to within one teaspoon? In my calculations, I only go to the tenths, since that's about the margin of error that varies because of topping off, and auto-shutoff points.

After 10 tanks (to hopefully cover the break-in period,) I'll try 5 tanks of 89, then 5 tanks of 87 again, and compare. Hrm. Although 5 tanks is such a long delay that seasonal differences will come in to play. Maybe I'll just try different octanes the next 3 times I go to Arizona in the fall. Compare over the course of 3 years, under as close as possible to the same circumstances. Since each drive will be about 5 fills, hopefully it will be a good comparison. I'll have the results for you in 2006. (That trip is about the only thing I do where my driving is the exact same each 'trip'.)

 

[Daniel]

You may want to try a couple of tanks of 89 octane gas. Although others on this forum say it makes no difference, on my car it gets between 4 and 5 mpg higher on 89. If you do the math, it is still a better deal taking the 45 mpg for 10 cents/gal, but I like to see the high mileage on MFD and the car seems a little more responsive with the 89.

Supposedly, octane rating is a measure of resistance to combustion, not energy content. Higher octane gas burns at a higher temperature, and is therefore required by higher-compression cars to prevent premature ignition. It prevents knock in engines that require it. But according to Click & Clack higher-octane gas actually has very slightly less energy.