MPG vs Temperature - Some Data

[dufusone]

Humidity can have a large effect on air conditioning load and perhaps engine performance. Air conditioning load in 90 degree weather will likely be different in Houston than in Phoenix. I don't know if this really applies to the issue here, but thought I would mention it.

[hdrygas]

I agree the data is what the data is. I wonder however at the effect of using average daily temps. Previous posts pointed out the differences between a cold engine in the am and a warmer engine late in the day. I may just be that the sample is too small. I wonder if you had enough sample if the other variables would tend to average out. I expect we need more people collecting data and I think we need data by the trip. I wish I had paid more attention in statistics.

[DaveinOlyWA]

the only way to track it is to take the average temps during the trip in question.

my take. record tank mileage by trip odometer (it measures .1) and mpg average on MFD. observe temps (may or may not change dramatically as you start moving. in the morning it rarely changes much. in the afternoon, it frequently drops several degrees after you start driving)

i observed higher mileage when warmer. no air on any of these. (if i used air, the results were discarded...should have kept them too) special attention to RT's to reduce the effect of weight of gasoline.

now most trips were short, 8.8 miles low speed, 25 mpg 10%, 40 mpg 25% and 35 mpg 65%. even with the shortness of the trip, the mpg average still went up but only consistsntly in the evening trips home which happened just after the warmest part of the day. (about 7-8 pm. sun doesnt set untill as late as 10 pm here) had drivers side window down 85% of the time on way home, only once in the morning. (there was no mpg change i could detect with window up or down. this was tested several times using a reference point after car was warmed up)

**other observations i saw. i am fairly certain that the weight of gasoline does play a part but will need to observe that again to make sure. unfortunately, it will be difficult if using any kind of climate control because of the effects of overall economy.

now because of the bladder system on the Prius, the usual pitfalls of doing this does not apply,(excessive water condesation) so i will devote at least a few months to checking on mileage obtained by only filling the tank partially. i want to make the observation in 3 groups of about a 1000 miles each to see if i can see any trend.