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I've noticed a pretty decent drop in MPG recently. I was wondering if maybe winter fuel was being rolled out, or if my driving habits have changed that much since I put my Bernie 2016 sticker on my car :confused:
 

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Don't know about US. In the UK it's Winter blend from October 15th to April 15th. They have an intermediate blend for most of the rest of the year and a kind of peak summer blend for sometime around mid June to Mid August - art least according to a document I saw from Shell.
 

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Definitely believe we are on winter blend now. My city MPG dropped about 5, and my last tank of gas was the lowest I have had since last winter.
 

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Winter Fuel is 10% Ethanol, 20% Butane, 70% Gasolene

Gasolene = 32.4 MJ/L

Butane = 26 MJ/L

Ethanol = 20.9 MJ/L

For every 10L you buy instead of 324 MJ pure gasoline you get (7 * 32.4) + (2 * 26) + (1 * 20.9) = 227 + 52 + 20 = 300 MJ

or for E10 (324 * 9) + 20.9 = 291.6 + 20.9 = 312.5 MJ

So you should expect an 8% decrease in fuel mileage vs pure gasoline or 4% decrease vs E10 (which itself is 4% below pure gasoline).

Obviously, other things effect fuel mileage.
 

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Winter Fuel is 10% Ethanol, 20% Butane, 70% Gasoline

So you should expect an 8% decrease in fuel mileage vs pure gasoline or 4% decrease vs E10 (which itself is 4% below pure gasoline).

Obviously, other things effect fuel mileage.
Thanks for posting this. I was unaware that much % butane goes into winter gasoline and this explains a few things to me.
The vapor pressure with warming butane may explain a transitory EVAP error code that crops up on my gen-1 car: sometimes occurring only in early springtime when temperatures get warmer.
This also may explain why the OBDIIC&C Gauge A/F parameter reads a value for stoichiometric ratio of only 14.3:1 vs. 14.7:1. [the MTBE, EtOh; C4H10, etc.]
fwiw: info indicates that the amount of oxygen contribution to winter fuel blend ranges up to 28% in some blends.
 
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