[quote author=bbf2530 link=topic=199631.msg4129429#msg4129429 date=1318428919]
[quote author=Big Jim link=topic=199631.msg4129359#msg4129359 date=1318405858]
Seasonal blended fuel does indeed still exist, even in California.
The primary reason for seasonal blending is two fold. In the winter, fuel that vaporizes easy is needed to start engines in cold weather. In the summer, such fuel vaporizes too easily and causes problems with vapor emissions and driveability as well as cutting fuel economy.
The index of this vaporization is RVP or Reed Vapor Pressure (or is it Reid, I forget). High RVP is needed in winter, and low RVP is needed in summer. Seasonal blending is always changing. My refinery friends tell me it is as often as every six weeks.
Another application of low RVP is piston aircraft engines. Altitude changes play hell on fuel vaporization. To enable starting in cold weather, airplanes use fuel heaters. From past experience I can tell you that when I ran aviation fuel in some of my old cars, that unless I kept about 20% to 25% pump gas, the engine would not start on cold mornings. Unfortunately, that was a dead giveaway that I had doctored fuel at the drag strip.
California may have stricter fuel requirements, including the need for cleaner fuels, but adding light ends such a butane in winter to raise the RVP is still done by necessity. Until cars have aircraft style fuel heaters, it is a necessity.
Hi Big Jim.
Yes, you are correct that seasonal blends do exist in some areas, that is why I qualified all of my statements with "most of us" (meaning not all), "essentially", "effectively" etc., to make it clear I was not making a blanket statement for all areas of the country. And yes, California is certainly an entirely different subject when it comes to regulations concerning emissions, fuel etc..
While I went into too much side detail on the winter gas, my basic intent was only to make it clear that contrary to what some people may believe, Fusion/MKZ/Milan owners do not
need to use 91-93 octane fuel in the winter. As per Ford, our cars are designed to run on 87 octane fuel nd using a higher octane blend on a factory tuned car will only lighten our wallets.
Sorry for the information detour on the winter gas formulations.
I agree with the fact that octane ratings above 87 are not needed for most Ford products. There are a few that should run higher octane fuel (like the Taurus SHO).
Ford published a TSB back in the 90's on the subject. I have no idea if it is still appropriate information. The gist of the bulletin was that the stuff blended into the fuel to raise octane also tended to aggravate cold start and light throttle stumble. This may be alleviated today by different fuel blending techniques or improved engine tuning. I mention this in support of your observation that higher octane fuel does nothing if it is not needed. I also mention it in support that that there is something historically that supports that Ford, at least back then, took the position that high octane may actually have a negative effect.