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Auto Club Explains Summer vs. Winter Blend Gasoline

Gas Prices, Automotive

State regulations dictate that retail gas pumps throughout Southern California should be filled with summer blend fuel by no later than Monday, April 1. Due to the early switch by refiners, which was followed by an earlier than anticipated gas price spike, gas pumps are already selling summer blend.


What does this mean and what is the difference between the two blends of gas?


The difference between summer and winter blend gas has to do with Reid Vapor Pressure (RVP) of fuel, according to the Automobile Club of Southern California’s Automotive Research Center Manager Steve Mazor. RVP measures how easily the fuel evaporates at a given temperature, said Mazor.


The higher the RVP, the more likely it will evaporate as the temperatures rise; and evaporated gas contributes to unhealthy ozone and smog levels, especially in the Los Angeles basin.


With higher temperatures in the summer, there’s a greater chance for evaporation, negatively impacting air quality, so summer blend is chemically engineered to produce a lower RVP, said Mazor.  High fuel volatility can even cause drivability problems (vapor lock) on hot days, especially on older vehicles, he added.  (Vapor lock is when the fuel in the fuel lines and fuel pump turns to vapor. The pump is designed to pump liquid gas, so when the fuel changes to a vapor state, the pump can’t supply enough fuel for the engine to operate, so it can stall, run rough, or not start.)


Summer blend is more expensive for refiners to produce and that cost is passed on to the motorist.  However, the US Environmental Protection Agency says summer-blend gasoline contains 1.7 percent more energy than winter blend, which is why gas mileage is slightly better in summer.  So, the upside is that fuel economy tends to be better with summer blend, according to Mazor, but as the switch from one blend to another occurs, motorists typically pay more to fill up.


Although prices have declined from their February peak, average prices for regular unleaded in Southern California regions still sit higher than where they were at the beginning of the year.

Since fuel prices tend to stay high for motorists during summer due to the more expensive blend the Auto Club wants to help motorists lower their gasoline costs.  By using simple strategies, car owners can obtain a reduction in fuel usage annually by up to 50 percent.


“Motorists can significantly reduce fuel consumption and save money by simply adjusting their driving style,” said Mazor.


“Driving style impacts motorists’ wallets because warming up an engine, speeding and ‘jack rabbit’ starts can needlessly increase fuel consumption,” he added.


Proper driving style and vehicle operation recommendations include:

  • Knowing the correct starting procedure for the car. Racing an engine to warm it up wastes fuel.
  • Maintaining steady speeds. A car uses extra fuel when it accelerates.  Cruise control may be a fuel saving option for motorists who drive a lot because a steady speed conserves fuel.
  • Minimizing braking. Anticipate traffic conditions. Be alert for slow-downs and red lights.
  • Using the air conditioner only when necessary. Air conditioning reduces fuel economy by about five percent and more in an older model vehicle. The rule of thumb on hot days is to open your windows when you are driving slowly (under about 45 mph), but close them and turn on the air conditioner at higher speeds. Driving with the windows open can increase the aerodynamic drag, and this effect increases proportionately with speed. A light exterior color and light interior cloth seats and tinted windows can reduce heat build-up, thus reducing the need for air conditioning.


Shopping for low gasoline prices in their local communities may save motorists money, according to Mazor, but traveling long distances to save a few cents wastes fuel and may cost motorists more money than they save.

CST 1016202-80 Copyright © Automobile Club of Southern California. All Rights Reserved.
The Automobile Club of Southern California is a member club affiliated with the American Automobile Association (AAA) national federation and serves members in the following California counties: Inyo, Imperial, Kern, Los Angeles, Mono, Orange, Riverside, San Bernardino, San Diego, San Luis Obispo, Santa Barbara, Tulare, and Ventura.