The Difference Between Summer and Winter Gas

Summer has its benefits: Fishing season. Dirt-track racing. Wrenching in the garage with the door open and the tunes blaring.

Another benefit is a slight fuel-economy boost. That’s because refiners alter their gasoline and diesel formulations depending on the season, and summer gasoline contains about 1.7 percent more energy than winter-blend gas. Regardless of the time of year, it pays to know a little about what’s going in your tank to ensure you’re properly maintaining your fuel system.

Under Pressure

A primary difference between summer and winter fuels is their Reid Vapor Pressure (RVP). RVP is a measure of how easily the fuel evaporates at increased temperatures. The higher the fuel’s RVP, the more easily it evaporates.

Winter-blend fuel requires increased RVP. If the fuel doesn’t evaporate readily in cold temperatures, the engine will start hard and run rough at cold temperatures.

To achieve this, refiners often blend winter gasoline with butane, a relatively inexpensive additive with a high RVP. They adjust the RVP of the final formulation to as high as 15.0 psi to help the gasoline ignite readily in the cold.

The Law Restricts Sales

Once the temperature warms up in summer, however, high-RVP gasoline can volatilize more easily, which contributes to increased emissions and air pollution. For that reason, federal law restricts sale of gasoline with an RVP greater than 9.0 from June 1 through Sept. 15. To comply, refiners reduce the amount of butane in the gasoline and instead use pricier additives, hence one reason gas prices generally increase in summer. The blending process also takes longer, adding to the cost.

Some areas set even lower RVP standards in summer to further limit emissions. California, for example, has a 70-psi limit. Given the state’s climate, refiners may sell summer-blend gas as early as April 1 and as late as Oct. 31.

For the most part, the semi-annual switch from winter to summer gas and vice versa happens seamlessly and goes unnoticed by drivers.

Lowest Additive Concentration

Regardless of the season, gasoline contains detergent additives designed to keep fuel injectors and other fuel-system components clean.

Some automakers, however, think the additive content, called the lowest additive concentration (LAC), is insufficient for modern vehicles. It takes a low level of additive to pass the tests, and most gasoline on the market contains as little as 123 ppm of additive.

The low levels of detergent additives in modern gasoline allow deposits to build up on critical fuel-system components, and most motorists are unaware of how dirty the insides of their engines are.

P.I.® and Upper Cylinder Lube

P.I. Performance Improver (API) is a potent, one-tank additive that deep-cleans your fuel system,

  • Cleans fuel injectors, intake valves and combustion-chamber deposits (See SLS Note below)
  • Reduces emissions and increases fuel economy up to 5.7 percent1
  • Use every 4,000 miles (6,437 km)

Upper Cylinder Lubricant (UCL) preserves and builds upon those gains, It also provides vital lubrication to the upper part of the cylinders,

  • Lubricates upper cylinders to fight wear
  • Inhibits ethanol-related corrosion
  • Keeps injectors clean
  • Delivers 18 percent more lubricity than Lucas* and 20 percent more than Sea Foam* for better retention of horsepower and fuel economy2

Reproduced With The Permission Of AMSOIL INC. All Rights Reserved.

AMSOIL Fuel Additives

AMSOIL P.I. (API) removes stubborn fuel injector deposits and improves fuel mileage an average of 2.3% and up to 5.7%1. Reduces emissions such as hydrocarbons (HC) up to 15%, carbon monoxide (CO) up to 26% and nitrous oxides (NOx) up to 17%. Restores power and performance. Reduces the need for costly higher octane fuel.

AMSOIL Upper Cylinder Lubricant (UCL) pinpoints your engine’s sparsely lubricated top-end to fight piston ring and top-end cylinder wear, maximizing engine compression and horsepower. AMSOIL Upper Cylinder Lubricant delivers 18% more lubricity than Lucas* and 20% more than Sea Foam for better retention of horsepower and fuel economy2

AMSOIL Quick Shot (AQS) for small engines & powersports equipment cleans fuel systems, addresses ethanol related performance issues and stabilizes fuel.

AMSOIL DOMINATOR® Octane Boost (AOB) maximizes power and improves performance in all two-cycle and four-cycle gasoline engines. Increases octane up to 4 numbers. Reduces engine knock, improves ignition and engine response, helps fuel burn cleaner and inhibits corrosion. Recommended for off-road and racing use.

AMSOIL Motorcycle Octane Boost (MOB) increases octane for power and efficiency. It is designed to improve startup performance and eliminate engine ping and knock for increased power at low-rpm operation. Contains detergents that help combustion chambers and fuel delivery systems maintain cleanliness for optimum performance.

AMSOIL Gasoline Stabilizer (AST) helps keep fuel fresh for up to 12 months. Fights oxidation to prevent the formation of varnish and sludge and keep floats and injectors clean for optimal engine performance. Ideal for stored seasonal equipment such as snowmobiles, lawnmowers, motorcycles and boats. Eases starting process when equipment is taken out of storage. AMSOIL Gasoline Stabilizer provides corrosion protection Sea Foam can’t match, helping maintain power and performance and keeping metal looking like new even when subjected to salt water.

AMSOIL Diesel All-In-One (ADB) combines the superior detergency and improved lubricity of AMSOIL Diesel Injector Clean, the excellent cold-flow and anti-gelling properties of AMSOIL Diesel Cold Flow and the increased horsepower and cetane of AMSOIL Cetane Boost in one convenient package. Provides as much a 32°F Better Protection against cold temperature gelling than Howes Lubricator Diesel Treat4 plus raises cetane up to 4 points. It is safe for use in all diesel fuels, including biodiesel.

AMSOIL Diesel Injector Clean + Cetane Boost (ADS) combines the superior detergency and improved lubricity of AMSOIL Diesel Injector Clean and the increased horsepower and cetane of AMSOIL Cetane Boost in one convenient package.

AMSOIL Diesel Injector Clean (ADF/ADFP) removes performance-robbing deposits from diesel fuel injectors to help restore horsepower and improve fuel economy. It is formulated for all types of diesel engines, including high-pressure common-rail designs.

AMSOIL Cold Flow (ADD) combats diesel fuel gelling by improving diesel cold-flow ability. It is formulated with an advanced deicer to enhance fuel flow and help prevent fuel filter plugging in cold temperatures. New formula treats double the fuel.

AMSOIL Diesel Cetane Boost (ACB) raises the cetane number of diesel fuel up to eight points for maximum horsepower, increased fuel economy and easier starts in all diesel engines.

AMSOIL Diesel Recovery (DRC) is an emergency diesel fuel treatment that dissolves the wax crystals that form when diesel fuel has surpassed its cloud point. Diesel Recovery liquefies gelled diesel fuel and thaws frozen fuel filters, avoiding costly towing charges and getting diesels back on the road. For preventative maintenance, use Diesel Cold Flow (ADD) or Diesel All-In-One (ADB).

1 Based on independent testing using EPA tests: Federal Test Procedure 75 (FTP), Supplemental Federal Test Procedure (US06), and the Highway Fuel Economy Test (HFET). Average fuel mileage increase of 2.3%.

2 Based on independent testing of AMSOIL Upper Cylinder Lubricant, Lucas Upper Cylinder Lubricant and Sea Foam Motor Treatment obtained on 2/13/19 using the ASTM D6079 modified for use with gasoline.

3 Based upon independent testing of AMSOIL Gasoline Stabilizer obtained Nov. 8, 2018 and Sea Foam Motor Treatment purchased Oct. 25, 2018 in a modified NACE TM0172 using synthetic sea water per ASTM D665 part B.

4 Based on independent testing in July 2017 of AMSOIL Diesel All-In-One and Howes Lubricator Diesel Treat using diesel fuel representative of the US Marketplace and Howes recommended treat ratio for above 0°F.

SLS Note: AMSOIL PI is an excellent product that has proven itself over the years however, if you have a gasoline direct injected (GDI) engine, fuel is injected directly into the cylinders after the intake valves. Because of this engine design it never comes in contact with the intake valves so it doesn’t get a chance to clean them. It does however do an excellent job of cleaning the injectors and upper cylinders.

*All trademarked names and images are the property of their respective owners and may be registered marks in some countries. No affiliation or endorsement claim, express or implied, is made by their use. All products advertised here are developed by AMSOIL for the use in the application shown.

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