My experience has been a direct parallel with the above post. By the way, there is no change in the signage at the gas stations I frequent : they are still tagged " 10% ethanol " What change would constitute a winter formulation ?
winter formulation is often mtbe (google) and reduces mpg's. it was here a long time before the great thinkers in washington decided ethanol was a good idea.
Winter formulations have been around ever since seasonal runability problems were noticed. Summer blends needed reduced vapor pressure to prevent vapor lock. Now this includes reduced pollution from evaporation. Winter blends needed higher vapor pressure to ease cold starts. MTBE and ethanol to reduce air pollution from combustion products came much later. The first link in Why mileage gets worse in winter has some more discussion about this.
