Winter Blend?
 

Is there a formula for when gas companies switch from Summer Blend to Winter Blend gas? Is it by temp or by a certain date each year?

Recently (mid to late Sept) I've noticed a significant MPG drop. Temps have been cooler, winds have been pretty high, but it still seems like more than that.

I realize all of the fluids/greases are at a higher viscosity now (mid 50s) than in summer as well, but the car is in the garage so the differences are not huge at this point (60s now, 80s in summer).

Thanks.


Jay

...GOOGLE "Winter blend gasoline"

...here's EPA document: http://www.epa.gov/otaq/regs/fuels/rfg/f01033.pdf

...quote from the EPA website:

"Volatility/Reid Vapor Pressure (RVP)

Volatility is the property of a liquid fuel that defines its evaporation characteristics. RVP is an abbreviation for "Reid vapor pressure," a common measure of and generic term for gasoline volatility. EPA regulates the vapor pressure of gasoline sold at retail stations during the summer ozone season (June 1 to September 15) to reduce evaporative emissions from gasoline that contribute to ground-level ozone and diminish the effects of ozone-related health problems."

Some gas stations here in Canada implement their Winter gas blends from November until early March I believe. I know my mileage takes a nose-dive when using those blends and when temperatures get really low (-20F).

35 MPG (winter blend) vs 40 MPG. (normal blend)

Here's the one from Petro-Canada : http://www.petro-canada.ca/en/wholesalefuel/318.aspx

I'm definitely of the opinion that the gradually decreasing temperatures this time of year do a lot to mask the effects of fuel blend changes. For all I know, the winter blends may actually give better mpg than the summer blend, if used under matching weather conditions.

I googled "winter fuel blend" and "winter blend gasoline", and learned a few things.

Most interestingly, it seems that the summer fuel is the blend that is a "revision" of the winter blend, not the other way around. Summer fuel must have a lower Reid Vapor Pressure, or RVP, otherwise it will boil within whatever container it is stored, at summer temperatures. I think this is what is called "vapor lock", and it's no fun when that happens to your vehicle. BTDT, over 20 years ago back in the old days. Given their choice, fuel blenders would provide "winter blend" year 'round because its ingredients are less expensive.

I found a reference stating that the shift to winter fuel begins on Sept. 15. It appears that this is the start of a gradual shift towards higher RVP blends, however I didn't find that explicitly stated.

Then there's the shift to summer fuel...
"...will require tank terminals to accept only summer grade RFG beginning
April 15 of each year... However, tanks at terminals must contain only summer grade RFG by May 1."

Here are some links re. summer/winter fuel blends:

A Primer on Gasoline Blending « EPRINC (a detailed article)

What's the difference between summer blended gasoline and winter blended gasoline? - Yahoo! Answers

HowStuffWorks "Why is summer fuel more expensive than winter fuel?"

HowStuffWorks "Summer-grade versus Winter-grade Fuel"

I and everyone I have talked to are seeing the biggest drop in fuel economy ever with the winter fuel this year. Around 15%.