How Long Can You Leave Gas in a Generator?

There has been a long debate about whether or not you can store away your generator with gasoline in it. Both options can be done if you follow the instructions in this quick article. 

Ethanol-free gasoline (or E10 at most) mixed with a fuel stabilizer can be stored in a 2-stroke or 4-stroke generator for up to 2 years, although not recommended. The generator should be kept from sunlight and the tank filled to the maximum recommended fill line.

Once you’ve added the stabilizer, run your generator for at least 10 minutes to ensure the treated fuel goes through the fuel system and the carburetor. Your final step is to shut off the fuel valve till the generator stops. This ensures there is no leftover gas in the carburetor.

Ethanol found in gasoline is the culprit that decreases the fuel’s shelf life. Most fuel sold in the US has about 10% ethanol, so I usually never ask.  Yet, beware that gasoline with more than 10% ethanol content is sold in the Midwest, so make sure you buy ethanol-free or at most E10 at the gas pump.  

E10 means a maximum ethanol content of 10% in gasoline.

E15 means a maximum ethanol content of 15% in gasoline.

E85 means a maximum ethanol content of 85% in gasoline.

Is it a good idea to leave gas for more than 6 months in a generator?

It is generally a bad idea to leave gas for more than 6 months in a generator. This will eventually wear out your generator due to corrosion and might cause clogging in the carburetor, so decide responsibly.

How much gas stabilizer do you need?

Every gasoline stabilizer manufacturer will have its own recommended ratio. Some generator manufacturers set their own recommended ratios depending on the model. Common fuel cans come in 1, 2.5, or 5-gallon sizes which helps with mixing the right amount of stabilizer.

STA-BIL recommends adding 1 ounce of their stabilizer to 2.5 gallons of freshly pumped gasoline for long-term storage of up to 24 months. 

STA-BIL’s Gas Stabilizer Dosage for Long-Term Storage

Gallons of gasOunces of Stabilizer
1Half an ounce
2.51 oz.
52 oz.
104 oz. 

SEAFOAM recommends adding 1 ounce of their stabilizer to 1 gallon of freshly pumped gasoline for long-term storage of up to 24 months. 

I can’t stress enough that the gas has to be fresh. Adding a stabilizer to old gasoline will not refresh it. 

James Jordan

Now, I do realize that SeaFoam is a much superior product. But, personally, I prefer using Stabil as it is more cost-effective and does a great job preserving gasoline. SeaFoam, on the other hand, is great for conditioning the engine and making it run smoothly. So you might want to run some SeaFoam product every few years to do some deep cleaning action to your generator’s engine. 

Of course, it’s easier to get the right ratio of stabilizer when you are storing gas for emergencies in a can.

But, 

What if you want to store your generator away till next winter? Fill your generator with enough gas to the maximum recommended fill line, and this way, you will know how much stabilizer you can add as per your generator’s tank size. An added benefit is a generator ready for action at any time.

Don’t worry if you end up adding a little extra stabilizer. Your generator will still run just fine after long-term storage. Just do your best to get it right.

Is Ethanol-free better for gasoline storage?

Non-Ethanol gasoline is best for storage as it can last for up to 6 months on its own. In comparison, E10 fuel has a shelf life of 3 months. A lesser amount of ethanol also means better fuel economy and less harm to your engine. Ethanol tends to oxidize and evaporate, damaging your engine over time. 

The downsides of non-ethanol gasoline are harmful emissions to the environment, more money out your pockets as it costs more to produce, and you’ll usually not easily find it at most gas stations. 

Go to pure-gas.org to find out the nearest gas station offering non-ethanol gas in the US and Canada. Ethanol-free gasoline just stores better.

How do fuel stabilizers work?

Fuel is volatile, which brings evaporation to mind. Fuel stabilizers, do as they say: stabilize the fuel! This means that the fuel will take much longer before its natural degradation process starts. 

Over time, Gasoline starts breaking down into separate components, losing its ability to ignite and combust due to oxidation and leaving a gummed-up carburetor, motor, and fuel lines. 

What if you have oil mixed with gasoline for a 2-stroke generator?

You can stabilize gas and oil mixtures as well. STA-BIL asserts on its website that it will work just as well on any engine type.  

What if I want to store my generator dry?

Manufacturers such as Champion have their own recommendations. Storing your generator dry is the responsible thing to do. Go to this page to find out Champion’s instructions on putting away your generator for both short-term and long-term storage.

However, some people have successfully left gas with a stabilizer in their generator for long periods and haven’t had any issues. So you are going to have to make that decision. Remember that manufacturers will tell you about their best practices to maximize their products life, but not necessarily what is practical for you. 

One last thing worth mentioning,

Champion’s recommendation “Add a properly formulated fuel stabilizer to the tank (2-3 times the manufacturer’s recommended amount)” goes to show that again every manufacturer will have their own specific recommendations.

So it’s best to make that decision on your own (depending on your generator’s brand) rather than listening to anecdotes on many different types and models!