Originally Posted by booster
Those of us in the frozen north see it every year when the seasons change
Most regions have their own blend requirements.
And these can change by State, County, Jurisdiction ( Tribal Lands) ad distributor
Even AZ has a winter blend for the Pima and Maricopa counties ( Tucson and PHX) as winter gives us inversions and bad air pollution- this is partly mitigated by oxygenated fuel ( ethanol).
Higher elevation regions have different requirements
at one point they tried 15%- but that caused other problems with fuel lines,seals and gaskets causing poor operation and raw gas spills....most vehicles won;t tolerate more than 10%
In general a fuel with 10% ethanol will deliver about 3% less mpg due to change in BTU's.
any other additives like deicer will reduce mpg as the "gasoline" portion is offset
when we used MTBE the mpg would be offset by same percentage as the additive