The Difference Between Summer and Winter Gas

The Difference Between Summer and Winter Gas & the Need for Fuel Additives.

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 7.0-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. This provides a great opportunity to sell the benefits of AMSOIL fuel additives.

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

• Reduces emissions and increases fuel economy up to 5.7 percent

• 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 economy.

For more information:
AMSOIL Fuel Additives.

Low-Volatility Motor Oil Helps Unlock Vehicle Performance

To meet today’s strict motor oil specifications and adequately protect modern engines, motor oils must demonstrate increased resistance to volatility. Nearly 30 years ago AMSOIL became the first oil manufacturer in the United States to use the NOACK Volatility Test (ASTM D5800) as a measure of performance excellence. Today, it’s an industry standard.

Why is Volatility Important?

Modern engines, particularly those equipped with performance-enhancing technologies like direct fuel injection and turbochargers, generate increased heat compared to their predecessors. At elevated temperatures, such as during severe service or when driving in hot summer weather, the oil’s lighter-weight molecules can volatilize, or literally “boil off.” The more volatile a lubricant is, the lower the temperature at which the lubricant will begin to evaporate. The more it evaporates, the less oil is left to protect equipment and the faster a user must replace the lost oil. You may have experienced this phenomenon by owning an automobile that “uses” motor oil in irregular intervals.

Volatility affects more than the rate of oil consumption. When light elements in oil evaporate from heat, the oil’s viscosity increases. This thicker oil forces the engine to work harder, resulting in several problems, including the following:

• Reduced performance
• Reduced fuel economy
• Poor cold-temperature starting
• Increased engine deposits
• Out-of-balance oil formulation, potentially leading to a higher concentration of additives than designed

NOACK Volatility Test (ASTM D5800)

The most common method used in measuring oil volatility is the NOACK Volatility Test. But that hasn’t always been the case. Originally developed and used in Europe, the NOACK test was not commonly used for lubricants until AMSOIL President and CEO Al Amatuzio pioneered its use for automotive motor oils in 1985. Previously, a lubricant’s flash point was the primary way to approximate an oil’s volatility.

In the NOACK test, an oil sample is weighed and heated to 250°C (482°F) for one hour. Dry air is passed over the sample, carrying the oil vapors that have boiled off and depositing them in a beaker. The original sample is removed and re-weighed. Any reduction in weight is reported as a percentage lost of the original weight.

Superiority of AMSOIL Synthetic Motor Oils

When AMSOIL began using the test, it was common for competitors’ conventional oils to demonstrate a volatility loss in the 17-25 percent range. In contrast, the volatility loss of AMSOIL synthetic motor oil was often less than half that. The NOACK Volatility Test introduced a new measure of performance to the industry, while allowing AMSOIL to distinguish the performance of its synthetic motor oils from competitors. 

Currently, API SN and ILSAC GF-5 performance classifications require weight lost due to volatility to be no greater than 15 percent for all viscosity grades of motor oil. General Motors’ proprietary dexos1™ motor oil specification is more stringent, requiring no greater than 12 percent weight lost.

AMSOIL synthetic motor oils are more stable and heat-resistant than conventional oils. They resist volatility to resist deposits and oil thickening, maximizing fuel economy and engine performance and life. 

NOACK Volatility of AMSOIL Synthetic Motor Oils

Performance Specification	API SN	ILSAC GF-5	GM dexos1™
NOACK Volatility Limit, % weight loss (g/100g) (ASTM D5800)	15%	15%	12%

Did You Know?

If a vehicle “uses” oil it may be due to the oil’s volatility. The light-weight molecules in oil evaporate more readily when exposed to high temperatures, causing the oil level to drop. Switching to AMSOIL synthetic motor oils, which resist volatility better than conventional oils, can reduce oil consumption and maximize engine performance.