Recommended Storage Practices
By: Chevron Corp.
This section presents storage recommendations of a general nature, followed by recommendations and comments for some specific uses or situations.
General Storage Recommendations Three precautions will delay the deterioration of gasoline:
General Storage Recommendations
Three precautions will delay the deterioration of gasoline:
The first two actions reduce the evaporation of gasoline during storage and reduce the exposure of gasoline to air and water vapor. The 5% air space allows room for the liquid gasoline to expand if its temperature rises.
If weather or storage conditions will keep the gasoline warmer than 80°F much of the time, add a fuel stabilizer additive to the gasoline. Fuel stabilizer additives are available at auto supply stores and some service stations and convenience stores. Follow the label directions. The best mixing is achieved when the stabilizer is added to the container before it is filled with gasoline. The stabilizer will work only if it is added to fresh gasoline; it can’t fix gasoline that has started to deteriorate.
Federal and California reformulated gasolines will survive storage as well or better than conventional gasoline.
Adding oil to gasoline doesn’t change its stability. Gasoline-oil mixtures for two-stroke-cycle engines will survive storage as well as gasoline itself.
Note: The volatility of gasoline is tailored for the range of temperatures expected in the locality where it is sold. Engines fueled with "summer gasoline" may be more difficult to start in cold weather. (See Volatility section, below.)
Store gasoline only in a container clearly intended for the purpose.
One, two, and five gallon containers should carry a sticker indicating they are approved for gasoline storage by the Underwriters Laboratories (UL). A plastic container has the advantage that it will not rust if the gasoline is contaminated with water or if the container is stored in a wet place.
A 60-gallon metal drum is the only container approved by the Uniform Fire Code for the storage of more than five gallons of gasoline.
The Uniform Fire Code limits the amount of gasoline in residential buildings to the amount "necessary for maintenance purposes and operation of equipment," not to exceed a maximum of 25 gallons.
Note that local Fire Department regulations may supersede the Uniform Fire Code. When storing more that five gallons of gasoline it is best to check with your local Fire Department for local regulations.
Do not store a container of gasoline near an ignition source such as an appliance pilot light.
This section applies to outboard motors, jet skis, snowmobiles, and lawn-and-garden equipment.
The owner’s manuals of many small-engine equipment recommend that the gasoline be less than 30 days old. They also recommend that the equipment not be stored with gasoline in the fuel tank. The tank should be emptied and the equipment run until the fuel line and carburetor also are empty. Both recommendations are intended to protect essential fuel system parts from gum deposits. While Chevron gasoline is stable for much longer than 30 days, it is Chevron’s policy to defer to the recommendations of the equipment manufacturer.
Follow the fuel and storage recommendations in the owner’s manual for your equipment.
Even if it is not recommended, draining the fuel from the equipment is the preferred practice when it is easy to do.
If fuel is left in the equipment, follow the general storage recommendations.
Equipment with a two-stroke-cycle engine requires fuel that is a mixture of gasoline and oil. While this mixture is as stable as gasoline, Chevron recommends not preparing more than you can use in a month or two because disposing of any excess is not easy.
Volatility describes a gasoline's tendency to form vapors. Liquid gasoline does not burn; only gasoline vapor burns. To start a cold engine, enough low boiling components ("light ends") must vaporize at the engine temperature to form a combustible vapor-air mixture.
This is one reason that the volatility of gasoline is tailored for the range of temperatures expected in the locality where is it sold. "Winter gasoline" has a higher volatility for easy starting in cold weather. "Summer gasoline" has a lower volatility because hydrocarbon vapor in the atmosphere contributes to smog formation.
The gasoline light ends needed for easy starting have the same tendency to vaporize in storage as they do in an engine. If the storage container is not tightly sealed, some of the light ends gradually will be lost. Too great a loss decreases the gasoline's ability to start an engine.
Evaporation of gasoline from a vented fuel tank or a can with a loose cap would be minimal if the temperature of the container were constant. But daily temperature changes cause the temperature of the container to cycle. The heating portion of the cycle raises the pressure of the gas (gasoline vapor and air) above the liquid gasoline which, in turn, drives some of the vapor-air mixture out of the container. The succeeding cooling cycle lowers the pressure of the gas, drawing fresh air into the container. Light ends evaporate from the liquid gasoline to saturate the new air. The daily repetition of this cycle gradually pumps light ends out of the container.
The cycle also brings air and water vapor into the container, especially during periods of high humidity. The oxygen in the air contributes to gum formation. (See Oxidation section.) And the water vapor, if it condenses during the cooling cycle, contaminates the gasoline with liquid water.
A larger volume of gas will be pumped in and out of the container when the air space above the liquid fuel is larger and when the daily temperature change is larger. Consequently, keeping the container almost full of gasoline and controlling the temperature fluctuations will minimize the loss of light ends, the exposure of the gasoline to air, and the contamination of the gasoline with water.
Except for any added oxygenates, gasoline is made up almost entirely of hydrocarbons – molecules constructed from the building blocks of elemental carbon and hydrogen. Hydrocarbons, as a class, are chemically stable molecules.
However, there are types of hydrocarbons (olefins and diolefins) that can combine slowly with the oxygen in the air ("oxidize") at ambient temperatures. The products of the reaction are larger molecules, collectively called "gum."
The gum-forming reactions become faster as the temperature of the gasoline increases. This is why this bulletin recommends controlling the temperature of stored gasoline.
Most gasolines contain negligible amounts of gum when they are manufactured, and most contain special chemicals ("stabilizers") to retard gum formation. It is the stabilizers that make it possible to store Chevron gasolines for a year when the conditions are good.
The gum formed by oxidation is usually soluble in gasoline. However, it remains behind as a sticky residue when the gasoline evaporates. Since gasoline begins to evaporate in the carburetor of a carbureted engine or in the injector of a fuel-injected engine, a gasoline containing soluble gum may leave a deposit on these parts and on the intake valves. These deposits will be in addition to the deposits normally formed by a gum-free gasoline — a formation triggered by the elevated engine temperatures.
Modern engines are designed to run best when vital engine parts are clean. Carburetor and fuel injector deposits can cause hesitation and stumbling on acceleration, lower fuel economy, lower power output, and higher emissions of hydrocarbons and carbon monoxide. Excessive intake valve deposits can cause many of the same performance problems, plus higher emissions of hydrocarbons, carbon monoxide, and nitrogen oxides.
Because the Federal Environmental Protection Agency recognizes that fuel system deposits increase emissions, they require all gasolines to contain a deposit-control additive. All deposit-control additives keep deposits from forming; the best ones clean up deposits formed by lower-quality gasolines.
If the gasoline contains a lot of soluble gum, the normal level of deposit-control additive may not be sufficient. This is why Chevron recommends treating a tank of gasoline with an extra dose of deposit-control additive if a vehicle displays driveability problems after being stored. (Note: Chevron does not recommend adding a deposit-control additive to the fuel for a two-stroke-cycle engine.) The gum-forming reactions become faster as the temperature of the gasoline increases.
Severe oxidation of gasoline may produce insoluble, as well as soluble, gum. The insoluble gum will take the form of brown or black particles which float in the gasoline or settle to the bottom of the container.
When an engine is fueled with gasoline containing insoluble gum, the fuel filter will remove the gum. If the engine has an in-tank fuel pump, the screen on the pump's feed also may capture some of the gum. However, these devices can become plugged if the gasoline contains too much insoluble gum. This will cause the engine to lose power or stall because it is starved for fuel. Adding a deposit-control additive will not keep insoluble gum from plugging filters and screens.
Storage, including storage involving gum formation, does not change the bulk properties and most of the performance characteristics of gasoline (excluding the characteristics affected by the gum itself). For example, storage does not change a gasoline's anti-knock index (octane) or energy content. However, these properties will change if the storage is accompanied by evaporative loss. The evaporation of light ends decreases a gasoline's antiknock index and increases its energy content.
Federal and California reformulated gasolines will survive storage as well or better than conventional gasolines. The regulations require reformulated gasolines to have less light ends and less olefins (federal, later; California, now) than conventional gasolines. As explained above, it is the oxidation of olefins that leads to gum formation. Reformulated gasolines also contain oxygenates. The common oxygenates are stable molecules that do not form gums.
Detecting Deteriorated Gasoline
The modes of gasoline deterioration are:
Moderate deterioration by any mode except contamination is impossible to detect without testing. However, testing by a qualified laboratory is impractical except when a large amount of gasoline or a very critical application is involved. While discarding deteriorated gasoline in an environmentally responsible way is not easy (see next section), it is the better answer for small quantities of questionable gasoline.
The evaporation of some low-boiling components is impossible to detect without testing. Relevant tests are:
If the first 10 volume percent of a gasoline distills above 160°F (summer) or 140°F (winter), the fuel no longer meets the ASTM specification for gasoline (Automotive Spark-Ignition Engine Fuel; ASTM D 4814).
A gasoline with a vapor pressure less than 5 psi (summer) or 9 psi (winter) is suspect.
Severely oxidized gasoline has a rancid odor and darker color. The presence of solid gum particles also may result in the loss of brightness and clarity. Testing is required to detect moderate oxidation:
Gasoline with a "washed gum" greater than 10 mg/ 100 mL is suspect.
Microbial activity tends to concentrate at the gasoline-water interface. Moderate activity may cause the gasoline to lose brightness and clarity. Severe activity may stabilize gasoline-water emulsions and contaminate the fuel with visible particles of microbial sludge (biomass). Anaerobic microbial activity may generate hydrogen sulfide, giving the gasoline a "rotten egg" odor.
The common contaminants are dirt, water, and rust (generated when gasoline and water are stored in a steel container). All of these contaminants can be detected visually. However, since they all tend to settle, a sample from the bottom of the container or fuel tank is required.
Disposing of Gasoline
It is not as easy to get rid of gasoline that has deteriorated. There are organizations that will help dispose of gasoline in an environmentally responsible way. Finding the best option may take some searching. Sources of information are your community's fire department, recycling center, and hazardous waste disposal center. Check the government pages of your phone book to locate these organizations. Commercial disposal organizations are listed in the Yellow Pages under Environmental & Ecological Services and Oils, Waste.