How Old Can Your Generator Gas Be and Still be Safe?

A gasoline generator, either in the form of an installed standby generator or a portable emergency generator, is an excellent prep that can keep the lights on and the power flowing through all kinds of emergencies, both long and short-term.

But the Achilles heel in any gas generator usage plan is the fuel itself. Gasoline is notorious both for its volatility and its short shelf life compared to other liquid fuels.

Baquieira gasoline generator

This means keeping a large quantity on hand and ready to use is logistically challenging, and old gasoline might fail to function or even be dangerous.

How old can your gasoline be and still be safe?

Depending on the type of gasoline, it will have a useful, safe storage life of between 3 and 6 months untreated, and up to a year if treated with a fuel stabilizer additive.

Although old gasoline is unlikely to become more dangerous due to its age, it is increasingly likely that it will produce malfunctions in your generator, fail to function at all, or even damage the generator itself.

There is a lot to consider if you are planning on storing a considerable quantity of gasoline to run your generator in an emergency. Though it is a tricky problem, it is one that must be solved because you can’t count on getting gasoline in the middle of an event! Keep reading to learn more.

How to store gas for your generator for years | Cooley

Gasoline Has a Short Storage Life

No matter how you square it, gasoline has a short storage life compared to most other liquid fuels. Generally speaking, you can only count on 3 months of safe storage life before your gasoline is significantly degraded for most consumer blends available in the United States.

If you are fortunate, a particularly high-quality brand of gas might get you 6 months on the outside, but not much longer than that.

When comparing gasoline to diesel, which can easily last upwards of a year in decent conditions with minimal maintenance, or propane, which can last three decades or longer so long as its pressure vessel is in good shape, gasoline seems kind of like a pain in the ass. Plentiful, cheap but short lived like a butterfly.

Ideally, we wouldn’t have to be constantly messing with and rotating our supply of gasoline that we keep on hand to fuel our generators.

As preppers, we have enough daily, weekly and monthly chores to contend with, and every additional task we add to the list soaks up more of our precious time, energy and mental bandwidth.

So what can we do to reduce this burden?

The Blend Makes a Difference

The single, easiest thing you can do to improve the storage life of gasoline is to track down and purchase a blend that does not have any ethanol in it. Most gasoline that you purchase at the pump here in America isn’t even real, true gasoline.

Instead, they are a solution, or blend, of gasoline and ethanol, and in pumps across America ethanol is being found in greater and greater proportion in our gas.

You can go talk to all the goober scientists and engineers you want regarding the efficacy of ethanol in gasoline and it’s supposed benefits, but car guys and savvy preppers know that ethanol gasoline blends pretty much suck compared to the pure, genuine article…

They are highly corrosive, and they have an extremely short shelf life because the components in the solution separate rapidly and when that happens, the fuel is useless and, even worse, can badly damage your fuel system or engine itself.

These ethanol gasoline blends will last for 3 months, 4 months on the outside if you are very lucky, and that is tops.

However, if you are able to track down a station or other supplier selling pure gasoline, you can take heart knowing that this gas will last twice as long as the adulterated blends that have become so common.

Pure gas will last about 6 months in storage before it should be considered seriously dodgy.

But considering how long we might have to wait between occasions when we need to fire up our generator, even 6 months doesn’t really feel like a long time.

Rotation Will Be Required for Any Standby Generator

It is important to understand right up front that any stored gasoline you have on hand for your generator, whatever kind it is, must be rotated. No, I’m not talking about turning the containers or the barrels; I am talking about refreshing your stocks!

“Rotating” your supply refers to the practice of periodically using up your oldest stock before it goes bad and then replacing it with the same quantity of new, fresh fuel. In this way, your oldest gas is always moving “up” toward replacement.

Considering you likely don’t have any cause to run your generator when using up this stored gasoline, you’ll need to come up with another purpose for it. Most folks, assuming the octane rating is compatible with their daily driver, will simply choose to fill up their automobile with it.

Other worthwhile uses include fueling of gasoline powered lawn equipment or mowers, recreational vehicles like ATV’s, go-karts and dirt bikes. Just try not to let it go to waste and definitely don’t pour it down a storm drain!

Consider the Use of Stabilizer Additives

There is something else you can do to extend the life of your gasoline. It comes at a cost, but adding a prescribed amount of fuel stabilizer additive to your gas and thoroughly mixing it can yield double or even triple the safe storage life. Sounds pretty good to me!

Although the process is as simple as it sounds, you must take care to ensure precisely the correct amount of stabilizer is added to a specific quantity of gas otherwise you risk ruining it or not obtaining the benefits.

Also know that stabilizers are fuel blend specific, not universal! This means you’ll need an ethanol-specific stabilizer for an ethanol gasoline fuel blend or a stabilizer that is specific to pure gasoline if that is what you have stored for your generator.

It is worth noting that pure gasoline benefits from stabilizers far better than ethanol gasoline blends and in conjunction makes a perfect option for storing a quantity of fuel for your generator.

Pure gasoline with the right stabilizer can give you more than a year of safe storage life, perhaps even 16 months!

If you don’t want to mess around with constant rotation of your gas supplies, definitely look into these stabilizer additives as they are well worth a little extra expense for the time savings and peace of mind that you will gain.


A gas powered generator is a great asset, but you’ll have to stay on top of maintaining and rotating the gasoline lest it go bad and fail to function or even damage the generator.

Old gasoline that has gone bad is not any more dangerous than normal, but the headaches that it can cause in the middle of an already bad situation or something that you cannot afford.

Seeking out pure gasoline or utilizing a fuel stabilizer additive is an easy way to extend the storage life of your stored fuel.

6 thoughts on “How Old Can Your Generator Gas Be and Still be Safe?”

  1. I run my generators once a month for about twenty minutes. Then I backfill the tank with FRESH gas. I keep the tank FULL. This keeps the airspace in the tank to a minimum, which slows the oxidation of the fuel. It also prevents condensation which will contaminate the fuel with water and will also lead to rusting of the tank.

    If you’re going to store your gennie long-term, PLEASE drain the tank and the fuel bowl on the carburetor! I come across them all the time at yard sales; generators that were used once and then shoved in a corner for years. By the the time they were needed again, the fuel in the bowl had solidified and the gas in the tank was useless toxic waste!

    I keep most of my fuel stores in a 55-gallon drum that I draw for my gas-powered equipment. When it gets down by five gallons I top it off. This helps keep the additives in the fuel fresh. I realize not everyone can or SHOULD keep that much fuel in one place, but the practice is the same; use it and refresh it.

  2. I decided when I was buying a genny not to go Gasoline for the these very reasons. They can limit size and be spendy but I chose LP gas instead of gasoline. I like the fact that propane never goes bad, it is portable enough, and fairly inexpensive. Also my home and my lake property (bug-out) are both in areas where they are remote enough it is plentiful if trading or scrounging becomes needed and it can serve multiple functions of heating and cooking fuel besides providing electrical power. If I had to marry myself to a fuel besides wind or solar it makes the most sense to me to make the most universal fuel I could find.

    • Indeed, propane has its advantages. Unfortunately, long term, it’ll get harder and harder to find; much faster than gas or diesel. My domino system; whole-house natural gas genny. The NG goes away, I’m down to one large and one small gasoline genny. Once that’s exhausted, it’s low-voltage solar charging deep-cycle batteries. Once that’s done, we’re down to candles and lanterns… Sooner or later though, you’re sleep cycle is going to mimic that of a chicken…

  3. I have a 4400 watt generator that I purchased in 2015. I try to run the unit once a month for 15 minutes for maintenance purposes. I have the same gasoline in it now for six years and the generator starts up on the first pull when the chock is properly set. I would imagine, based on this article, that I’m pushing the limits with the older fuel still in it but it runs great Any thoughts concerning this?

    • I used two year old off road gas with stabizer for my chain saw and weed whacker with no problems. After two years old when some is left, I cut it in half with fresh fuel. I run them dry and take the fuel out after the season is over to air dry with caps open.


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