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Re: Anyone else notice MPG's changing ???

On  8 Nov 95 at 18:45, LToy@aol.com wrote:

> Right you are.  Exact dates vary from area to area, but Nov 1 to Feb 28 (29)
> is common for the "oxygenated" fuels.  I see about a 15-20% drop in mileage
> with my '91 200q.
> You use the term "winter blends."  In years past, winter blends meant
> something different--specifically different volatility/vapor point and
> slightly lower octane level, especially in the nortnern climes (this is
> probably still true today).  folks more informed than I can probably expand
> on this.  I don't know how much this would affect mileage.
> I am somewhat suprised that you see that much drop with your '86 4kcsq--your
> car doesn' have the engine management systems that respond to fuel
> differences. I never noticed this much change when I had my '87 4kcsq (2.2L
> 115bhp motor)
Oil companies have had different winter and summer blends for years.  
In the winter you want a more volatile blend, ie you want it to form 
a vapor at a lower temperature for easier starting on cold mornings.  
In the summer, though, the temperatures are obviously higher, and 
more of the gasoline would evaporate out of the tank or pump, making 
more smog, thus a less volatile blend.  There are other 
considerations, too, but I don't remember what they are.  Anyhow, 
more governmental concern about the environment has led to changing 
regulations concerning these blends (especially the summer blends), 
but the oil companies had the different blends anyways, for 
non-environmental reasons.  I'm not sure how this relates to 
oxygenation and mileage...
Oh yeah, don't assume that the winter blend in Denver is the same 
winter blend sold in Boston, or that the winter blend at Total is the 
same as Sunoco's winter blend.  And, obviously, the same goes for 
summer blends.

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