How Long can you Leave Gas in A Generator?

How Long can you Leave Gas in A Generator?

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There are many reasons why you might want to store your portable generator with gas in it after a dry camping trip.

Perhaps you’re a seasoned RVer who goes boondocking a few times a year. Or your power needs are low, reducing your generator use.

That means you have a portable generator in your RV, garage, or in the back of your truck that is sitting with gas in it for extended periods.

The question is: what happens to the gasoline that may have to sit in the tank for weeks or even months without any use? How long can you leave gas in a generator before it goes bad?

Read on to find out.

Table of Contents

How Long can you Leave Gas in a Generator?

The length of time gasoline can be stored depends on factors like the type of gas, how and where it is stored. 

It is important to note that gas will naturally degrade with time due to a process called oxidation. However, the duration of time varies depending on the type of gasoline you’re using.

Generally, gasoline sold at your local gas station will last between one to three months. Whereas, other types of gas have a longer shelf life.

Ethanol blended gas will last up to three months

According to Energy Information Administration (U.S), gasoline sold at your local gas station is “E10” which consists of 90% petroleum-based gas and 10% ethanol

Ethanol blended gas (aka regular gas) has a shelf life of about three months. This is because ethanol oxidizes quickly as it readily absorbs water from the air.

The oxidation process gradually contaminates the fuel resulting in the fuel separating into a layer of gas and ethanol, making the gas bad.

Generally, the higher the ethanol content in the gas, the quicker it will oxidize and become unusable. This means E15 (15% ethanol) or E85 (85% ethanol) gasoline has a shorter shelf life compared to E10 gas.

Pure gasoline will last up to six months

Pure gasoline is different from regular gas because it doesn’t contain any ethanol. However, that doesn’t prevent pure gasoline from oxidation.

Because of the lack of ethanol content in pure gas, it oxidizes slowly compared to ethanol-blended gas. This increases the shelf life to six months when stored properly.

Fuel Stabilized Gas will Last up to Three Years

When it comes to extending the shelf life of gasoline, nothing beats a good fuel stabilizer (Buy at Amazon). A fuel stabilizer is an additive that is mixed with gas before storing the generator to slow down the oxidation process.

Depending on the age of the gas in the fuel tank, most fuel stabilizers can extend the shelf life to between one to three years. However, stabilizers best work with new gasoline and maybe ineffective on old and contaminated gas.

Read More: Can you use too much fuel stabilizer in your generator?

Properly Stored Gas will Last up to Six Months

Gasoline will degrade and lose its combustibility with time due to the effect of oxidation and evaporation. But the process can be slowed when it is stored properly, which is about half a year.

When storing gas in the fuel tank, make sure to fill up the tank to its recommended level. This reduces the amount of oxygen in the tank, restricting the oxidation process.

Furthermore, make sure the fuel tank or fuel container (Buy at Amazon) used to store gas has an air-tight cap. This will further reduce oxygen from entering and fumes from exiting.

Additionally, store your generator or fuel container in a cool and dry place to further extend its shelf life.

It is difficult to track the age of the gasoline you pump in your generator. Fuel starts aging from the day it is produced and stored in the refinery. It may have to sit in the reserve tanks of a gas station for some time depending on how busy the station is. By the time you purchase the gasoline, it may already be a few weeks to a month old.

What Happens if I Put Old Gas in my Generator?

Running a generator with old or bad gas can have a lot of adverse effects on the generator’s overall health, performance, and functionality.

Generally, with time, gasoline loses its ability to combust making your generator use more fuel to produce the same amount of power. This will increase the amount of money spent on fuel.

On the other hand, contaminated fuel running through the generator fuel system will deposit and gum up the internal parts of the generator. These deposits will increase frictions in the internal components, resulting in your generator overheating.

Furthermore, the increased friction and added heat will pace up the wear and tear of the internet parts. This will shorten the working life of your generator or prevent it from working altogether.

Drain your generator fuel tank if the fuel is very old and or contaminated. However, you can add fresh fuel to your old gas if it is not badly broken down. Alternatively, you can use a fuel booster (Buy at Amazon) to recharge your old gasoline and add some of the combustibility it lost with time.

How do I know if my Gasoline is Bad?

As gasoline sits in your generator fuel tank or storage tanks, it oxidizes and loses its combustibility before becoming stale. There are several symptoms of bad gas in the generator you can look for.

Because gasoline loses its ability to combust as it gets old, especially ethanol-blended gas, the generator will have difficulty starting. In addition, your generator will sputter, knock and produce unusual sounds when it is supposed to run smoothly.

If your generator is sitting in storage with fuel in it for an extended period, you need to inspect the fuel visually before firing up the unit. For visual inspection, drain a little bit of gasoline out of your generator fuel tank into a clear glass.

Now, into a second glass pour in some freshly pumped gas of the same type. Now compare the two side by side.

Generally, as the gas ages, its color deepens and has a sour or rotten smell. A darker shade or smell indicates that the gas has lost part of its combustibility but is not contaminated.

However, if you notice separate layers in the glass or find debris or sediments, then your gasoline is contaminated. It is important to note that trying to run a generator with contaminated gas will damage the unit.

How to Extend the Shelf Life of Gasoline?

There are a few easy and effective ways to keep your gas from going bad in your generator tank. 

The first is to run your generator with load for 15 minutes every two weeks. This will refresh the fuel in the fuel system of your generator and prevent it from getting stagnant. Moreover, exercising your generator a few times a month will drain the fuel tank, forcing you to pump fresh fuel.

The next tactic to prevent fuel from going stale is to fill up the fuel tank of your generator to the recommended level. This will leave less room for oxygen and moisture in the tank, thus slowing down oxidation.

If you plan to store your camping generator for over a year or two, then consider adding a fuel stabilizer (Buy at Amazon) in the fuel tank. This will keep your gas fresh for about three years, keeping you worry-free.

Lastly, if you plan on storing fuel in a jerry can (Buy at Amazon) then consider purchasing high-quality airtight fuel containers. Gasoline stored in airtight containers, at the right temperature and humidity level will remain fresh for long period. However, make sure to follow government guidelines and purchase a fuel container of no more than 5 gallons.

Where should I Dispose of Contaminated Gas?

Once you find out the gas in your generator has degraded beyond repair, you need to dispose of the contaminated gas. 

Never dispose of even the most broken-down gasoline into a dustbin, drain, sewer, or any water body. Gasoline is highly flammable and can contaminate water bodies.

You need to contact your local fire department to find the nearest government disposal area.


The answer to the question “how long can you leave gas in your generator” will depend on the type of gasoline you’re using. Generally, ethanol-blended gas has a shelf life of about three months and pure gas six months.

However, if you plan on storing your generator for more than a year consider adding a fuel stabilizer to your gasoline. This will keep the fuel in your generator in top working condition for one to three years.