Post by Steve BarkerI'd like to see some documentation (legitimate documentation) that
proves this theory of gasoline being blended different in the winter.
A crash course on seasonal gasoline
...First, one of the biggest differences is the RVP (Reid Vapor
Pressure) of the gasoline. Winter gasoline made for cooler climates
has a higher RVP number- meaning it is more volatile. The higher RVP
number means the gasoline in your tank is under more pressure. This is
why come warmer months, the RVP number must be lower, or the high
pressure could result in the gasoline boiling or evaporating, causing
an increase in air pollution.
Second, winter gasoline contains more butane. Butane doesn't burn as
clean as other "ingredients" in gasoline, but it is far cheaper to mix
into gasoline. With the added butane in winter gasoline, you may
notice that fuel economy suffers until the warmer months, when
refiners cease using as much butane in each gallon. Butane has the
highest vapor pressure of just about any other ingredient, coming in
over 50psi, which is why summer gasoline doesn't use as much. If it
would, the RVP number would be as high as winter gasoline...
Read more at
http://blog.gasbuddy.com/posts/A-crash-course-on-seasonal-gasoline/1715-401024-239.aspx
What Is Summer-Blend Gas?
And if it's so clean, why don't we use it year-round?
By Sam Schechner
...Summer-blend gas isn't new. It was first sold in 1995, as required
by the Clean Air Act's 1990 amendments, and the current, even cleaner,
concoction was phased in for the summer of 2000. Since then, there
have been sharp spikes in fuel prices every spring as summer blends
get rolled out. This is not so much because it's expensive to make the
gas—the added cost per gallon is only 1 or 2 cents—but because
refineries generally try to sell every last bit of winter fuel before
mixing in the slightly more expensive summer batch. Sometimes they
draw down the stock too far, creating shortages before the first
deliveries of summer blend enter the supply chain. The return to
normal blends in the fall causes a far less pronounced spike because
the industry, free from summer standards, doesn't bother selling off
the summer gas before mixing in the less pricey stuff.
So why not use the summer blend year-round? The main reason—apart from
the fact that the 1990 law isn't written that way—is that summer-blend
gas doesn't work as well in the winter. Summer blend's low-evaporation
rate makes engines less likely to stall in hot weather but can make
them difficult to start in the cold...
Read more at
http://www.slate.com/id/2098672/
Refining 101: Winter Gasoline
...Winter gasoline blends are phased in as the weather gets cooler.
September 15th is the date of the first increase in RVP, and in some
areas the allowed RVP eventually increases to 15 psi. This has two
implications for gasoline prices every fall.
First, as noted, butane is a cheaper blending component than most of
the other ingredients. That makes fall and winter gasoline cheaper to
produce. But butane is also abundant, so that means that gasoline
supplies effectively increase as the RVP requirement increases. Not
only that, but this all takes place after summer driving season, when
demand typically falls off.
These factors normally combine each year to reduce gasoline prices in
the fall (even in non-election years). The RVP is stepped back down to
summer levels starting in the spring, and this usually causes prices
to increase. But lest you think of buying cheap winter gasoline and
storing it until spring or summer, remember that it will pressure up
as the weather heats up, and the contained butane will start to
vaporize out of the mix.
And that’s why gasoline prices generally fall back in the fall, and
spring forward in the spring.
http://www.consumerenergyreport.com/2007/09/14/refining-101-winter-gasoline/