Reminder to keep seasonal variations in mind
 

I just wanted to issue a reminder to everyone to keep seasonal variations in mind when reporting results. As weather changes, particularly temperature, FE results will get skewed. Just to prove the point, I recently made this plot from my daily log data from the last 2 years, showing average fuel economy for every month:
http://ecomodder.com/forum/member-di...ab-display.png
http://ecomodder.com/forum/member-di...thly-temps.png

Jun-Aug are typically good months because it's so warm, Jan & Feb not so much. Keep this in mind as your looking at and reporting the effects of mods. A-B-A testing is of course the best way to do things if you can. The issue with only A-B testing is that weather conditions (and other factors) can artificially skew things. So, as things cool down, don't be discouraged if you see little or no increase in FE numbers. And, when things warm up, be careful to not inflate the beneficial effect of a certain mod.

Plotting MPG (Y-axis) vs. TEMP (X-axis) makes a rather interesting datum which enables you to "predict" (albeit poorly) the ±MPG changes vs. ±TEMP changes.

Agreed.

When ABA testing my side skirts late at night, as the night wore on and the temperatures dropped, my mpg's slowly dropped across the board on "A" runs and "B" runs, thus skewing my results.

don't forget gasoline blend changes in some locale when the season changes. E85 really does a number on my Prius. I go from just over 50MPG then as soon as the gas pump starts pumping E85 into my Prius, MPG goes down into the low 40's. It shouldn't be that bad but it is!! I don't think engine computer in my Prius like the E85. How else can I explain such a huge drop off.

Let's just say that ethanol doesn't provide any power then for each gallon I still have .85 gallon of gasoline. so my MPG should only be down to 85% of my summer driving. But it isn't. It's far less. And I have driven without changing my habit just to see. no heating nor AC and it still is worse than 85% of my summer MPG.

Only thing I can think of is that Prius engine computer doesn't like E85... :( So is E85 really help with SMOG and air pollution?? Has anyone really looked into it?

I'm not so sure about E85.

And if you look at carnot cycle, with colder ambient and same burn temperature in the cylinder, we should see slightly better efficiency. So something else is happening.

I didn't realize a Prius could run 85% alcohol? Are you using a conversion kit?

In New England, we always have 10% alcohol in the fuel. I always thought the winter fuel had more oxygen, but I guess it's more butane according to this article; HowStuffWorks "Summer-grade versus Winter-grade Fuel"

Oops. I thought E85 meant oxygenated gasoline. Oxygenated gasoline is required in LA area and Portland Or during the winter month. www-dot-epa-dot-gov/OTAQ/fuels/gasolinefuels/winterprograms/index-dot-htm

I was talking to Toyota service manager last year and he said that MPG would drop a LOT because of oxygenated gasoline and that my car and the engine is fine. Not to worry is what he said to me.

taking a mental note on what E85 stands for so I wont make the silly mistake. Thanks

I love modding all winter to see the results in the spring :)