Summer Gas = MPG

[mojoman]

I just drove over 500 miles in my Promaster fully loaded and averaged 19.2MPG. I noticed the summer blend here in CA gave me almost 2 MPG more on this trip compared to winter trips. I could have gotten better if I didn't have to drive through the Bay area.

[markopolo]

I've noticed the difference in MPG between summer & winter diesel blends. On one trip returning north from visiting south the mpg dropped with the first fill up in Maine and didn't improve on the second fill up.

[booster]

Those of us in the frozen north see it every year when the seasons change. The winter gas is higher volatility, lower vapor pressure so it will burn in the cold better, but it also has about 2% less energy in it. The drop in energy in one part of the mileage loss, but the other is that it alters the burn rate in the combustion chambers (faster) which can affect the efficiency of the whole setup. I think it would require a valve and ignition timing change to counteract it.

With more recent odd ball, extreme, weather changes we seem to get a lot now, it is pretty common for the gas suppliers to get caught with winter mix in the tanks during an early hot spot spell. Lots of cars stumbling on acceleration and other issues until they catch up with the gas. The always wait until the last minute anyway, as winter gas is apparently cheaper to produce.

You will find some engines are much more sensitive to the changes compared to others, just like they are with ethanol blends. Some will hardly show a change in mileage, and some will be very noticeable.

[mkguitar]

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


mike

[Ron J. Moore]

Thanks to all for elaborating and explaining the ethanol, it was really informative. Ron