Is It Bad to Leave Gas in a Generator? – Spruce Generator (2023)

When a power outage hits, most people rush to fill their generators with gas to stay prepared. However, the power outage might last for less than an hour, leaving your generator with a lot of gas. Now, you start asking yourself how long you can leave gas in a generator.

You can leave gas in a generator for 4-6 months after draining the fuel line from the fuel valve to the engine. You can extend this duration by adding a fuel stabilizer, which extends the period to 1 year. If not, drain all the gas in your generator and store it in a storage can, but you’ll still need to add the stabilizer.

Why should you not leave gas in a generator for too long? What happens if you did? How well should you store the fuel? These are the topic I will be discussing in this article. You might want to read more to understand how to handle fuel in a generator.

Why Should You Not Leave Gas in a Generator

If you leave gas in your generator for too long, probably for years, it might not go too well for you and your generator. Here common issues you might face if you left gas in your generator.


Regular gasoline is subject to oxidation. The air in the fuel tank is needed to allow expansion and allow gas to get burned; it oxidizes the fuel when it sits in there for too long. Oxidation starts to cause corrosion to the fuel tank, and that leads to fuel degradation.

Stale Gas

Even though gasoline is hygroscopic, it doesn’t blend with water, but rather it expels it. However, since regular gasoline we buy from a gas station, a small percentage of ethanol attracts the water from the environment.

When water mixes with ethanol, it’s okay to a certain extent. According to research, a gasoline-ethanol mix can even absorb almost 1-half to 1% of its volume of water and stay blended.

After this point, the separation phase occurs. The water overloads the blending and creates alcohol, thus separating from gasoline to create a substance that a generator engine cannot consume.


Another problem that most people might not be aware of is the microorganisms. Some microbes do pretty well in ethanol-enhanced gasoline. Scientists say ethanol might be attracting them, and when they get inside, they feed off it.

Like humans, they need to excrete. Their excretions are considered acidic, which can slowly corrode the fuel tank and other metal parts.

Carburetor Blockage

Your generator fuel line should not stay with fuel for more than two weeks, from the fuel valve to the engine.

A generator carburetor is so tinny that its fuel jet, responsible for blending air with fuel, cannot even fit a needle.

If a drop of water was to get into the fuel line, it could overwhelm it, causing other air-gasoline mixing problems.

How to Use Fuel Stabilizer to Extend Fuel Lifespan in a Generator

Gasoline is an unstable liquid. When left in a generator fuel tank to sit around, it can quickly go bad. The spoiling might even start as early as 30 days unless the tank is fully airtight, which is not possible.

Even though draining your generator could be the best protective measure, you can extend the fuel life span in a generator is to use a fuel stabilizer. The substance can prevent fuel oxidation.

What is a Fuel Stabilizer?

A fuel stabilizer is a formulated liquid or solution designed to provide a protective layer that sits on gasoline to prevent oxidation.

In short, it’s a mixture of lubricants and antioxidants ideal for repelling water and reducing evaporation.

It’s mostly made from petroleum products that allow it to bond with gasoline. Doing so prevents the fuel from going bad or forming a sticky resin that blocks or ruins the carburetor.

When Should You Use a Fuel Stabilizer

If you are using your generator daily, you don’t need a fuel stabilizer for a project around the house or something. In such a case, the engine consumes the gasoline before it can evaporate or go bad.

However, if your generator is for emergencies only and you’re forced to keep it with gasoline to be ready, adding a fuel stabilizer is an excellent idea.

With the lifespan of fuel stabilizers varying with a brand, most of them can preserve your fuel for a whole year. A higher dosage can increase the protection but is not recommended.

How to Use a Fuel Stabilizer

Using a fuel stabilizer might seem like a simple pour of a capful into the fuel tanks, but that isn’t the case. It’d be best to follow these steps to give your generator fuel maximum protection.

Step 1: Measure the stabilizer

Read the product’s usage instructions in the user’s manual to know how much you need to add to your fuel tank.

Step 2: Add the stabilizer into the fuel tank

Make sure your generator’s fuel tank is nearly empty. Measure the recommended amount of the stabilizer and pour it inside.

Step 3: Fill the fuel tank with fuel

Add gasoline to the fuel tank until it’s complete. That will help disperse the stabilizer and mix it with gasoline. It would also ensure the tanks has little air or water space left.

It’s always best to go for ethanol-free gasoline. Ethanol is the problem-causing agent in regular gasoline. Eliminating it can have your fuel last for few years.

Step 4: Run Your Generator

The next step is to start the generator engine and allow it to run for 5-10 minutes. That will allow the fuel stabilizer to distribute to the entire fuel system.

How to Drain Gas from a Generator

If you won’t be adding any fuel stabilizer or if a year is over since you added the fuel stabilizer, you’ll need to drain the fuel and dispose of it.

Of course, running the generator to the last drop is the option until it shuts down. The same steps apply when you want to drain old or stale gas from a generator.

Take your generator to a well-ventilated area to allow the fumes to escape and concentrate in one place and creating a fire hazard. It can be outdoors, in a ventilated shed, or open garage.

Open the fuel tank cap. That allows the air to flow in and out. If the generator has a cover, open it to have easy access to its fuel lines.

Locate the fuel valve switch and set it off by sliding it towards the off marking. By doing so, you will be preventing the gas from spilling when opening the fuel drain in the next step.

Follow the fuel line from the fuel valve and locate a pinch clip connecting the fuel valve tube to the carburetor.

Remove the clip and point the fuel drain to a bucket or a container. Open the fuel valve and allow the fuel to drain. Once all the fuel has drained, reconnect the fuel line and close the fuel tank cap.

Locate the carburetor using the generator’s user manual. On the side, there is a drain bolt; open it and drain the remaining gas out.

If you have a carburetor cleaner, you can spray it from both ends, especially when dealing with old or stale gas.

Return the drain bolt and cover the generator.

Related Questions

Is letting a generator run out of gas okay?

You cannot allow your generator to run out of gas. If you do and repeatedly, your generator might lose the necessary residue magnetism in the alternator coils. If that were to happen, the generator would run but produce zero voltage. You can read more about letting your generator run out of gas here.

What are the signs you left gas in your generator for too long?

If you experience any of the following symptoms, which might happen all at once, you have bad gas in the fuel tank or carburetor.

  • Stalling
  • Difficulty starting up
  • Higher emissions
  • Rough idling

Don’t Leave gas in a Generator for Long – Friendly Tip

If you don’t plan to use your generator for more than two weeks, make sure you close the fuel valve and drain all the fuel in the carburetor. If you don’t plan to use your generator in the next 4-6 months, add a fuel stabilizer to extend its lifespan for another 6-months. Else drain all the gas in the generator and store it properly.

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