Is there really a difference between summer and winter gasoline? YES! Many areas around the USA will switch to a “winter blend” of gasoline once the weather starts becoming colder. This has been a common practice for most of the USA since refining crude oil many years ago. In fact, there are over 20 different blends of gasoline in the USA today. The question remains, why do we even have two different blends of gasoline?
Different Grades of Gasoline.
The reason there are so many different grades of fuel boils down to controlling Volatile organic compounds (VOCs). The reason state and federal agencies try to control VOC levels is due to smog and the environmental impacts. VOCs evaporate much better in warmer temperatures where the heat allows the atmospheric ozone and the VOCs to combine, thereby increasing the amount of smog.
Reid Vapor Pressure (RVP) is a system of measure used to grade gasoline. It is vapor pressure measured at 100 degrees Fahrenheit. This system uses a measurement of PSI (pounds per square inch) and all gasoline blends have to be below 14.7 PSI, or the gasoline would turn into a vapor. The higher the RVP number is, the easier it is for the gas to vaporize, making it that much worse for the environment.
The lower the RVP of a gasoline, the more “pure” it is and the greater the cost.
During summer, the higher average temperatures mandate that the RVP of fuel has to be lower in order to maintain its fluid state. The EPA has set mandate for RVP levels during the summer time: 7.8 PSI to 9 PSI based on region. There are many different gas blends because the average temperatures in the USA will vary greater from one area to another.
For example, the temperature in Miami will differ greatly from the temperature in Seattle. The average temperature and state and federal mandates will ultimately determine the RVP of fuel in various regions during the summer.
During the colder winter months, gasoline is not as pure as it is during the summer. The colder weather allows refineries to mix gasoline with other agents, such as Butane, which diminishes the quality of the fuel. The RVP of butane is 52, so it is almost never used in summer fuel because it would allow a much greater chance for the gasoline to turn into vapor. The additions of agents like butane make gasoline during the winter time less pure and therefore worse for your fuel system and your miles per gallon.
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