Rajan Wilcox
Gasoline is a blend of processed crude oil that includes more than 100 hydrocarbons as well as chemicals that prevent rust. The combustibility of gasoline is dependent on its chemical composition, which limits its shelf life. Gasoline that has been sitting for a long time will eventually go bad, but it can still be treated using a fuel stabilizer or by adding fresh gas. The octane level of gasoline can decrease within months, especially when stored under less than ideal conditions. The higher the octane rating, the better the air-fuel mixture and the combustion in the cylinders. However, the use of higher octane fuel than is recommended for a vehicle is generally considered a waste of money.
| Characteristics | Values |
|---|---|
| Fuel loses octane | Over time, fuel loses octane and its combustibility. |
| Factors that affect the rate of octane loss | The type of fuel and how it is stored. |
| Fuel type | Ethanol-blended gasoline ages faster than regular unblended gasoline. |
| Storage | Gasoline can be stored for up to about six months in airtight containers. |
| Preventing octane loss | Fuel stabilizers can extend the shelf life of gasoline. |
| High octane fuel | 93-octane fuels are more refined and stable, lasting two to three times longer than 87-octane fuel. |
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What You'll Learn
Fuel stabilizers can prevent fuel degradation
Fuel stabilizers are a great way to prevent fuel degradation and keep your fuel tank running smoothly. They are designed to maintain the quality of stored fuel, preventing engine problems that might reduce fuel efficiency. Fuel stabilizers can be used for all kinds of gasoline and diesel engines, including two-stroke and four-stroke engines. They are also suitable for small engines like lawnmowers, snowblowers, and generators.
The optimal time to add a fuel stabilizer is when fueling up, especially if the vehicle or equipment will be stored for 30 days or more. Fuel stabilizers can help keep the fuel from becoming stale or oxidized, prevent water accumulation, and ensure easy start-up after extended storage. They can also prevent the formation of gum and varnish in the engine, which can cause engine problems and reduce fuel efficiency.
It is important to read the product instructions on the brand of stabilizer you purchase. Typically, you will need to add the stabilizer to a nearly empty tank, measure the correct amount, and then pour it into the gas tank. Then, run the engine for 5-10 minutes to allow the stabilizer to reach the entire fuel system.
Some fuel stabilizers are better suited for long-term storage than others. For example, Star Tron's Enzyme Fuel Treatment is specially formulated to prevent ethanol fuel problems, which can cause faster degradation. It's important to note that fuel stabilizers are not a miracle solution, and they only help slow the aging process of fuel. However, they can effectively prevent fuel degradation and keep your fuel system running smoothly.
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Gasoline with ethanol degrades faster
Gasoline with ethanol does degrade faster than ethanol-free gasoline. Ethanol-free 91 octane gasoline will last longer than 93 octane gasoline containing ethanol, despite the latter having a higher octane rating. This is because ethanol is more susceptible to degradation than gasoline. Even with proper storage, 87 octane gas can start to degrade in three months, whereas 93 octane gasoline can last up to nine months before degradation is noticeable.
Ethanol is a popular fuel additive in the United States due to its inclusion being mandated by the Renewable Fuel Standard (RFS) and its updated version, RFS2. The RFS requires that about 10% of all gas-engine fuel sold in the US be ethanol, which is typically blended as E10. Higher concentrations, such as E15 and E85, are also available in some locations.
The presence of ethanol in gasoline can cause issues for older engines and fuel systems. Ethanol can cause seals and hoses to deteriorate, shrink, or swell, resulting in leaks. Additionally, ethanol can pick up contaminants that gasoline doesn't, which may be deposited inside the engine, leading to fouled filters or injectors and decreased engine performance. Engines that are rarely or seasonally used, such as lawnmowers or chainsaws, are especially prone to these issues.
To mitigate the potential problems caused by ethanol, some steps can be taken. Proper formulation and care of ethanol blends by fuel transporters and resellers are improving over time. Additionally, for older engines, ensuring that seals and hoses are not weak or susceptible to degradation is crucial. Using ethanol-free gasoline, while less common, is also an option for those concerned about the potential drawbacks of ethanol-blended fuel.
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High-octane fuels are more refined
High-octane fuels are indeed more refined than their lower-octane counterparts. This is because they contain more stable hydrocarbons, which can last two to three times longer than those in lower-octane fuel. For example, 87-octane gas can start to degrade in as little as three months, even when stored properly. On the other hand, 93-octane fuel can last up to nine months before any degradation is noticeable. This is because lower-octane fuels tend to be less refined and contain more unstable hydrocarbons, which react over time to form gums, varnishes, and lower-octane hydrocarbons.
The octane rating of a fuel is a measure of its ability to avoid "knock", which occurs when fuel prematurely ignites in the engine's cylinder. This degrades efficiency and can damage the engine. Knock is virtually unknown to modern drivers due to the presence of oxygenates in fuel that prevent knock by adding oxygen to the fuel. The higher the octane number, the more resistant the fuel is to knock.
To achieve a high octane rating and a consistent composition, pure chemical components are mixed with highly refined gasoline. The higher boiling point of these chemicals also means that vapor pressure decreases are less common until the fuel is exposed to temperatures above 80°F. Additionally, high-octane fuels are more stable when it comes to storage and have a longer shelf life.
It is worth noting that high-octane fuels are still susceptible to octane loss and vapor pressure decreases due to butane evaporation. While they may offer superior stability, the main downside to using high-octane fuels is the cost. However, even in a car that only requires 87-octane fuel, there are no negative reasons not to use high-octane fuel, as it can help clean the fuel system.
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Octane loss can cause engine knocking
Octane ratings are important indicators of a fuel's performance. The octane rating indicates the likelihood of the fuel to experience "knock", also known as detonation or autoignition. Knock or detonation occurs when the air-fuel mixture has already started to burn, and it produces undesirable pressure waves that can damage the engine. This can be caused by higher-than-normal temperatures or a hot spot in the cylinder, which leads to pre-ignition. Pre-ignition occurs when the air-fuel mixture ignites before the spark plug fires.
The octane rating, therefore, becomes a crucial factor in preventing engine knocking. Higher octane ratings indicate a higher resistance to knock. Racing fuels, for example, have different performance characteristics like burn rates and cooling factors, and not all racing fuels with the same octane rating will perform the same. Some fuel components act as burn accelerators, while others help with vaporization. The burn rate must be fast enough for the air-fuel mixture to combust within the cylinder.
Octane loss can occur in fuel stored over long periods, especially in less than ideal conditions. This loss can also occur in fuel stored in vehicles that are parked for extended periods. Octane loss in fuel can lead to engine knocking, as the resistance to knock decreases with the reduction in octane rating.
To prevent octane loss, fuel stabilizers can be added if a vehicle is to be parked for more than three months. Additionally, higher octane fuels, such as 93-octane, are more refined and contain more stable hydrocarbons, lasting two to three times longer than 87-octane fuel.
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Gasoline loses combustibility over time
Gasoline does indeed lose combustibility over time. The length of time it takes for gasoline to go bad depends on the type of fuel and how and where it is stored. Generally, pure gas begins to degrade and lose its combustibility in three to six months if stored in a sealed and labelled metal or plastic container. However, fuel stored in a car tank can begin to degrade in as little as a month.
Ethanol-blended gasoline, such as E10 or E85, which contain 10% and 85% ethanol respectively, has become increasingly common in the US. However, ethanol-gasoline blends have a shorter shelf life of one to three months.
The chemicals that give gasoline its combustibility limit its shelf life. The more volatile hydrocarbons evaporate first when gasoline is stored for a prolonged period, so the fuel becomes harder and less efficient to burn. The remaining hydrocarbons then degrade over time. This process is called oxidation, which happens when oxygen comes into contact with gasoline. Oxidation breaks down the hydrocarbons and forms deposits that clog parts of the fuel system, causing the car to run poorly.
Hydrolysis is another process that occurs when moisture, like humidity, mixes with fuel. The fuel then becomes corrosive and allows rust to form. Bad fuel, especially gas containing ethanol, can also draw in water vapour, which can corrode the tank and fuel system.
To prevent gasoline from going bad, it is recommended to use a fuel stabilizer additive, which extends the shelf life of gasoline by slowing down the chemical reactions that cause it to degrade.
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Frequently asked questions
Yes, fuel can lose octane in your gas tank over time. The rate at which octane is lost depends on the type of fuel and how it is stored.
Gasoline typically lasts a month or two without any issues. However, gas that is more than two months old may cause minor decreases in performance, and gas older than a year can cause issues like engine knocking and clogged injectors.
To prevent octane loss, fuel stabilizers can be added to the fuel. Topping off the tank with fresh gas can also help, as the new gas will mix with the older gas, and the engine computer will adjust for any variance in octane.
