Temperature Correction
 

Browsing through the EPA's site and their testing methods I noticed that they keep their lab VERY warm when testing FE. 68-86?F (20-30?C) making an average temp of 77?F/25?C (0?C is 32?F. Add or subtract 9?F for every 5?C raised or lowered).

Hmmm...since I bought the Metro in Sept. 2005 I'm certain that we've only had 10 to 15 days of weather over 20?C in my area. I have actually been recording temperature over the last few tanks and the average last fill was 11.2885?C.

I've noticed that Motor Trend, Hot Rod, and most auto mags will often correct 1/4 mile times to compensate for altitude, temperature, and such, so why shouldn't we at various times of the year...especially in -20?C weather when I struggle to get 35 mpg out of the Metro...:D . Here's what I came up with:

Based on some collected data and a guesstimate my Metro gains/loses 1% fuel efficiency for every 1?C rise/fall. My last average recorded temperature was 11.2885?C and my last three-tank average was 43.041 mpg. Using the EPA lab's average temperature, my temperature correction is:

25 - 11.2885 = 13.7115 (this becomes the percentage rise in FE)
43.041 x 13.7115% = 5.9016 mpg gain
43.041 + 5.9016 = 48.9426 mpg

A calculation like that might be useful to determine if your car is operating correctly, but at the end of the day it does not alter the the number of miles you traveled or the quantity of gas you consumed.

It's also good info to have if you're a nerd for the data, right Meto95? ;) Just for the sake of knowing.

And hey, maybe it could be useful... perhaps you could plan your trips to take advantage of temperature. (Well, it's a possibility for me at least, since I work at home and just use the car for errands & social stuff. :D ) You probably won't be surprised to learn that I have already started doing that - putting off trips until the warm part of the day when I can.

And welcome to the site, GeoMetry! You've got an interesting handle - am I right to guess you're a Suzukiclone driver? If you feel like introducing yourself, start a Hello thread in that forum.

Cool calculation. I'd like to be able to contribute some data, but as you know I don't have a regular car use pattern to refer to.

I plan to do another MPG vs speed plot sometime this summer. I'll make sure I revert any mods back to the way the car was when I did that run so it can be a direct comparison based on temp.

I'm as curious as you are to find out how much my mileage has changed due to rising temps vs driving technique (which is ever-evolving).

Right! And if I actually do hit 48 mpg or higher in 25?C average temps then I won't feel the least bit disappointed in 35 mpg during -25?C weather!

Weather was amazing earlier this month and my average temp was 21?C for a week (car ran incredibly well in 30?C). Average temp is now down to 16?C (and falling) since it hasn't been above 12?C for the past week.