What You Should Know About Winter Blend Gasoline.

November 7th, 2013 by

Few conversion van owners, or drivers for that matter, are aware that the gasoline bought in the summer is quite different from the blend that comes from gas stations in the winter.  Interestingly, the composition of gasoline sold in the winter months is chemically distinct and costs less to produce. It is for this reason that gas prices tend to sink in the colder months.

The topic of differently blended gasoline has not made true headlines until recently with the publicity in California from statements made by Governor Jerry Brown. Brown suggested that the increased use of winter-blend gasoline would help the state lower gas prices, which have exceeded those in most other states in the country.

There are at least 20 different blends of gasoline sold around the country due to the differences in regulations in each state. The reason why so many different blends exist is due to the efforts of refineries to reduce the appearance of volatile organic compounds (VOCs) from gasoline when it’s sent through an internal combustion engine.

One of the reasons why smog tends to occur more frequently in the summer is because VOC levels increase in hotter weather. Gasoline is graded based upon its Reid Vapor Pressure (RVP) level, and to prevent VOC levels from rising out of control in the summer, gasoline blends are modified to reduce how many VOCs are released into the atmosphere.

To prevent gasoline from behaving abnormally during the summer, it must be blended at a particularly low RVP level, which is measured by a PSI level. Normal atmospheric pressure sits at 14.7 PSI, but summer gasoline blends must sit somewhere between 9.0 PSI and 7.8 PSI. These numbers are mandated by the federal government and the Environmental Protection Agency (EPA).

Each state tends to have a separate timeline for introducing winter blends of gasoline, and the average PSI also differs by region. Different schedules create different prices across the country. Because creating gas that has a lower RVP costs more, summer gasoline tends to be more expensive. The increase in the amount of butane used during the winter, which evaporates more quickly, makes gas mileage suffer. However, the lower price of winter gasoline does tend to offset the loss in fuel economy.

Although the drop in demand for gasoline in the colder months does tend to influence lower gas prices, the primary reason for the drop in cost is the different blend. Refineries spend less money to produce winter gasoline, and as a result motorists receive a small break on gas prices. Likewise, the savings due to the increase in fuel economy during the summer is absorbed by higher average prices at the pump.

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