"Does gasoline go bad?"
"Can I still use the gasoline in a car that hasn't been driven for six months?"
"What changes when stored for a long time?"
Many people probably have such questions when their car or motorcycle has been left unused for an extended period.
The conclusion is that gasoline changes state over time.
Gasoline is not a single substance but a fuel made from a combination of various hydrocarbons.
Even during storage, it is affected by:
Air.
Temperature.
Light.
Moisture.
Storage container.
Therefore, it's not a case of "it will stay in the same condition forever if kept in the tank."
This time, we will explain in an easy-to-understand manner what changes occur when gasoline gets old, what to be aware of with cars that have been unused for a long time, and the relationship with fuel additives.
Does gasoline degrade?
Yes.
Generally, gasoline changes its properties over time.
ENEOS also states that fuel oils such as gasoline are affected by light, storage temperature, moisture, and contact with air.
Therefore, it is not possible to simply say:
"It's absolutely safe for X days from purchase."
This is because the condition varies greatly depending on the storage environment.
For example, in:
Environments with poor sealing.
Places that get hot.
Places with extreme temperature fluctuations.
Environments where moisture can easily mix in.
The fuel's condition is more likely to change.
Why does gasoline go bad?
One of the main factors is "oxidation."
When components in gasoline react with oxygen in the air, the fuel's properties change over time.
As oxidation and subsequent reactions progress, sticky byproducts called "gum" can form.
If these byproducts accumulate in the fuel system, they can affect the operation of:
Narrow fuel passages.
Injectors.
Carburetors.
Valve areas.
In fact, the formation of gum due to fuel oxidation, leading to fuel system clogging, is an important topic in research on fuel storage stability.
Gasoline "volatility" is also a factor
Gasoline contains many components with different evaporation rates.
Therefore, in environments where sealing is insufficient, more volatile components may be lost.
This means the composition will no longer be exactly the same as when it was purchased.
Gasoline is a fuel designed with considerations such as:
Easy engine starting.
Proper vaporization.
Stable combustion.
Therefore, if only some components change, it can affect starting performance and combustion conditions.
What can happen with old gasoline?
Although it varies depending on the fuel condition and vehicle, gasoline left for a long period can lead to problems such as:
-
Difficulty starting the engine
-
Unstable idling
-
Hesitation during acceleration
-
Engine not performing at its best
-
Dirt accumulating in the fuel system
Honda also states that "fuel deterioration" can occur if a car is not used for a long period, and advises consulting a dealer about using it after long-term storage.
Especially in small engines using carburetors, old gasoline remaining in narrow passages can lead to difficulty starting.
Yamaha also notes that if gasoline stored for a long time degrades, small holes inside the carburetor can clog, making starting difficult.
How long can gasoline be stored?
It's impossible to definitively say "X months are always safe."
This is because it varies greatly depending on storage conditions.
ENEOS states that while they don't set a quality retention period, a general guideline for gasoline, kerosene, and diesel is about six months if stored properly in a cool, dark place with minimal temperature changes.
However, this does not guarantee quality within that period, and early use or replacement is recommended.
Therefore,
"Six months is absolutely fine" is not true.
Conversely,
"It's definitely unusable after a few months" also cannot be said for certain.
The important thing is:
How it was stored.
Is a car's fuel tank safe?
A car's fuel tank is designed to safely hold gasoline.
However, that doesn't mean the gasoline completely stops changing.
If a car is not driven for a long time, the condition of the entire vehicle can change, including:
Fuel.
Battery.
Tires.
Rubber parts.
Metal parts.
Oils.
In other words,
Instead of thinking, "If there's fuel in it, it will run fine after six months," it's important to check the condition of the entire car after long-term storage.
Moisture also needs attention
When storing fuel for a long time, moisture is also a critical factor.
Due to temperature changes and storage environment, moisture can enter the fuel system.
Especially with gasoline containing ethanol, it's necessary to understand its relationship with water.
Ethanol has a high affinity for water, so it will absorb water up to a certain amount.
However, if the amount of moisture exceeds the limit, "phase separation" can occur, where the fuel separates into gasoline and an ethanol-water mixture.
The US EPA also explains that phase separation occurs in ethanol-blended gasoline when the moisture content exceeds a certain amount.
This does not mean it necessarily happens with all commercially available gasoline in Japan.
The important thing is to:
"Prevent water from entering the fuel."
Can I judge by the color or smell of gasoline?
With fuel stored for a long time, changes such as:
Darker color.
A distinct, altered odor.
Cloudiness.
Visible foreign matter.
may be observed.
However, it is difficult to accurately judge fuel quality based solely on appearance or smell.
Just because it looks normal does not mean it is of the exact same quality as new fuel.
Conversely, a slight difference in color does not immediately mean it is unusable.
If you are concerned about the condition of the fuel in a car that has been left for a long time, it is safer to consult a dealer or repair shop.
What if there's "gasoline from last year" remaining?
For example:
A motorcycle not ridden at all during winter.
A sports car stored for several months.
A generator left unused for a long time.
In such cases, attention to the fuel's condition is necessary.
Especially if it has been left for nearly a year or more,
It is safer to check the condition of the fuel and vehicle before repeatedly trying to start the engine, thinking, "Let's see if the engine starts."
Sending old fuel through the fuel system could potentially worsen problems.
Is old gasoline okay if I top it up?
Some people might think:
"If half of the old gasoline remains, it should be fine to fill it up with new gasoline, right?"
However, this also depends on the fuel's condition.
Has it simply been a few months?
Has obvious deterioration occurred?
Is there water or foreign matter mixed in?
Has it been left for a long period?
The judgment changes depending on the conditions.
Adding new gasoline does not make existing degradation products or the water itself disappear.
Instead of self-judging and diluting fuel of unknown condition, it's recommended to have it checked by a professional if necessary.
Does premium gasoline last longer?
You might think:
"Premium gasoline is higher quality than regular, so it must be more resistant to long-term storage, right?"
However, that's not what it means.
Premium gasoline does not equate to long-term storage gasoline.
One of the major differences between premium and regular gasoline is the octane rating, which indicates resistance to knocking.
ENEOS also describes octane rating as "a measure of resistance to knocking."
Therefore, just because it's premium doesn't mean it will never degrade.
Both are affected by the storage environment.
Is it better to store gasoline with a full tank?
When researching long-term storage, various information appears, such as:
"It's better to fill it up."
"It's better to have less fuel."
"It's better to drain it all."
This is because the recommended method varies depending on the vehicle type and machinery.
For example, for some generators, manufacturers instruct to drain gasoline from the fuel tank and carburetor if not used for a long period. Honda also advises draining fuel from generators if they won't be used for 30 days or more.
On the other hand, the structure of fuel tanks and fuel supply systems in automobiles differs.
Therefore,
Instead of a uniform approach like "all cars should be full" or "drain everything," it's essential to follow the vehicle or equipment's instruction manual.
Is it okay to store gasoline long-term at home?
Gasoline is a highly flammable and dangerous substance.
Therefore, it is necessary to avoid storing it in containers not designed for gasoline, such as:
Beverage bottles.
Plastic bottles.
Kerosene poly tanks.
General plastic containers.
When handling gasoline, you must follow not only appropriate containers and storage methods but also regulations like the Fire Service Act.
Instead of self-judging, "Let's store a large amount for disaster preparedness," please check the guidance of fire departments or other relevant organizations if necessary.
How to dispose of old gasoline?
Old gasoline should not be discarded into:
Drains.
Gutters.
Soil.
Rivers.
Gasoline is highly flammable and harms the environment.
Also, attempting to burn it yourself for disposal is extremely dangerous.
If you need to dispose of old fuel, please consult a dealer, repair shop, or a professional fuel handler.
Acceptance methods vary by business, so it's recommended to confirm before bringing it in.
Can fuel additives revive old gasoline?
This is an important point.
Fuel additives have various purposes, such as:
Cleaning.
Oxidation inhibition.
Corrosion prevention.
Fuel stabilization.
Combustion enhancement.
However, they are not meant to:
"Restore degraded gasoline left for years back to new."
Fuel that has already significantly deteriorated.
Fuel with a large amount of water mixed in.
Phase-separated fuel.
Fuel with foreign matter.
It's best not to assume that simply adding a fuel additive can restore such conditions to like-new.
Fuel additives are not something that:
Unconditionally revives old fuel,
but rather are meant to be:
Used according to the specific purpose of each product.
What is the relationship between Gelhorn 3+ and old gasoline?
Next Science's Gelhorn 3+ is a product focused on fuel conditioning and combustion.
It can be used with gasoline, diesel, and kerosene, with a recommended dosage of 0.5ml per 1L of fuel.
However, it is not positioned as:
"A product for restoring gasoline that has degraded due to long-term storage back to new."
This distinction needs to be made.
First, the fuel itself must be in a normal state.
Only then can one consider the conditioning of the fuel and combustion.
This order is important.
If significant deterioration of fuel left for a long period is suspected, please check the fuel's condition before adding an additive.
Things to check in a car not driven for a long time
If a car is not used for a while, it's necessary to check not only the fuel but also:
Battery.
Tire pressure.
Engine oil.
Brakes.
Coolant.
Rubber parts.
Rust on metal parts.
Honda also mentions that long-term storage can affect not only fuel degradation but also rubber parts, tires, batteries, and metal components.
In other words,
An undriven car for a long period does not mean that simply changing the gasoline is the end of it.
Basics for using gasoline in good condition
There's no need to overthink it.
The basics are:
Don't store it longer than necessary.
Use appropriate fuel.
Prevent water or foreign matter from mixing in.
If not used for a long period, check the manufacturer's storage instructions.
Do not force its use if abnormalities are detected.
It's easier to understand gasoline as a fuel to be used while it's in an appropriate state, rather than a "product to be stored."
Summary: Gasoline changes over time
Gasoline is not a fuel that maintains the same condition indefinitely, even when stored for a long time.
Its condition changes over time due to factors such as:
Air.
Temperature.
Light.
Moisture.
Storage environment.
As a result, it can affect:
Starting performance.
Combustion conditions.
Fuel system.
The important thing is not to:
Only look at the number, "X months are absolutely safe."
It is necessary to comprehensively consider:
What kind of environment was it stored in?
How long has the car been undriven?
Is there any abnormality in the fuel?
Is there any problem with the entire vehicle?
And regarding fuel additives,
Instead of thinking of them as "something that revives old gasoline,"
It's important to understand the purpose of each product and use it accordingly.
When considering the condition of your car, don't just focus on the engine; also pay attention to the:
Condition of the fuel itself.