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Anybody know when we will switch over to summer gas or has that already happen?
The transition varies by state based on weather/temperature differences of geography. However the core dates for summer gas (i.e. when everyone has it) are 6/1 thru 9/15 based on federal regulation. Warm weather states like California and Texas can sell summer gas as early as 4/1 and as late as 10/31, and some states like Arizona sell just a single blend year-round.

Summer blend has +2% energy value over winter blend, so you should expect to see at least that increase in mpg - aside from warm weather helping hybrid battery/mpg.

https://www.caranddriver.com/news/a15339380/the-vapor-rub-summer-versus-winter-gasoline-explained/
 

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I started trying to find the exact difference between winter blend fuels and summer blend (there are over 20 different blends in the USA at any given time).

Biggest things I've been able to confirm, winter blend has a lower evaporating point (generally represented in the form of RVP (Reid Vapor Pressure) rating.) Most winter blend fuels use simpler and lighter additives such as butane which is more volatile (affects RVP), but has less energy content than Octane. The additives in winter mix are generally cheaper, and require little maintenance to switch over from summer blend. This combined with less driving during winter months is why winter gas is cheaper.

Summer Blend gasoline generally contains heavier additives, to help reduce volatility. The major purpose of this is so that the gasoline doesn't evaporate before reaching the cylinder, preventing vapor lock, and reducing emissions. The additives for summer blend are harder to implement in the refinery process, so the gas companies tend to do their yearly maintenance at the same time as the fuel switch. The downtime, and more expensive additives are why every spring we see a spike in fuel prices.

The EPA estimates the energy content of Summer fuel is 1.7% greater than winter fuel, which has a small impact on fuel economy.

How Stuff Works, Fuel Blends
 

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There wasn’t a change this year for mid-Atlantic states, due to the Philadelphia refinery going kaboom in June.
 

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It was more of there wasn’t summer blend this year so we have been technically on the winter fuel this summer.
 

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There wasn’t a change this year for mid-Atlantic states, due to the Philadelphia refinery going kaboom in June.
It was more of there wasn’t summer blend this year so we have been technically on the winter fuel this summer.
Oh, bummer - so you've had "winter mpg" all year then. But it'd be an interesting comparison point...

Your summer fuel economy would have only benefitted from warmer temps, since winter gas was a constant factor. What mpg differences have you seen cooler temps vs warmer temps while on winter blend?
 

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I drive a touring but been around 45 mpg due to what I was doing this summer doing a lot of short under 1 mile trips for work and also the terrain I drive on which is have probably 200-400 ft elevation change in both going up and down. But when I drove over 10 miles I average around 55 mpg on rural roads going 50mph but drop down to 50 mpg going 65 plus on interstates/ divided highways. With the heater on the longer journeys are like 45-48.
 

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We finally have a real cold streak here in Florida LOL (ok ok - it's was in the 60's today) but the last week or so I have noticed a decrease in gas mileage regardless of temperature. How do I know if winter blend gas has come to Florida?? My MPG's have fallen from 52-56 down to 43-47..
 

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We finally have a real cold streak here in Florida LOL (ok ok - it's was in the 60's today) but the last week or so I have noticed a decrease in gas mileage regardless of temperature. How do I know if winter blend gas has come to Florida?? My MPG's have fallen from 52-56 down to 43-47..
Looks like there's variation within Florida, from law that was revised in 2014 for Miami, Tampa and Jacksonville (Broward, Dade, Duval, Hillsborough, Palm Beach and Pinellas counties)... so it may depend on where you last bought your gas (?).

Summer blend is typically 7.8 PSI, but the update in allows higher 9.0 PSI which can introduce range. The first article below mentions that 2014 was the first year Florida remained on a 9.0 blend thru summer. The second article is the EPA detail on 'relaxing' the summer blend requirement in states including Florida.

https://askthetrucker.com/no-more-summer-gas-blend-for-florida-north-carolina/
https://www.epa.gov/gasoline-standards/gasoline-reid-vapor-pressure
 

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Discussion Starter #14
Gasbuddy confirms we've switched to summer blend but it will take a few more weeks for gas stations to get rid of their current supply. :D
 
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