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Fuel Foresight: When Does Gas Expire and How to Make It Last?

Its been suggested that just like spoiled milk can ruin a meal, expired gas can put a damper on your road trip. But is this true? how long does gas last? Learning how to make gas last longer before it starts to expire and how to use a fuel stabilizer can save you from unexpected engine troubles. 

Today, we’re taking a closer look to uncover if gas expires and how and when a fuel stabilizer might improve your stored gasoline. Before you rev your engine and hit the road, let’s dive in!

What Causes Gas to Go Bad?

Gasoline can go bad due to several factors, like evaporation, oxidation, water contamination, and microbial growth. The volatile compounds in gasoline evaporate over time, leading to a decrease in octane rating and performance. Exposure to oxygen can result in the formation of gum and varnish-like deposits which can clog fuel systems. Water entering the gas tank can cause corrosion and engine issues, while certain microorganisms can thrive in the fuel, causing further degradation. Finally, some fuels have additives that can react with each other and cause unwanted characteristics.

To what degree all of these different degradations happen will depend heavily on how and where the fuel is stored. Modern storage attempts to reduce exposure to oxygen, moisture, and heat. Use approved containers designed for fuel storage and tightly seal them. Store the gasoline in a cool, dark, and well-ventilated area, away from direct sunlight and heat sources.

Gas pumps at gas station
Gasoline can expire or go bad from several factors.

How Long Does Gas Last?

How long gas lasts before it starts to expire depends on various factors. These factors include its formulation, storage conditions, and the presence of a fuel stabilizer. On average, modern gasoline can last for about three to six months without any significant issues when properly stored. Modern vehicle tanks are well-sealed to prevent airflow and help keep it from going bad quickly.

However, if stored in open containers in hot environments, fuel can go bad within a month. However, with a fuel stabilizer and proper storage, it can retain its quality and extend its shelf life up to two years.

Pro Tip: Get more bang for your buck by uncovering Should You Put Ethanol-Free Gas in Your Tank?

How Long Does Diesel Last?

Unlike gasoline, diesel has a longer shelf life due to its lower volatility. When you store it in suitable conditions, diesel manufacturers state it can remain usable for up to one year or even longer, making it a more resilient fuel in terms of storage. Personally, we have known people who have used diesel fuel stored in underground tanks for 5+ years without any problems as long as fungicides and algaecides have been added.

diesel tank treatment
While diesel lasts longer than gasoline, the longevity increases the likelihood of alge or fungi to grow in the tank. By using additives to prevent this we have stored diesel for years without any problems

How to Tell Your Gasoline Expired

Recognizing if your gasoline is expired is essential to preventing potential engine problems and maintaining vehicle performance. If your stored gas or vehicle has been sitting longer than the standard gasoline shelf life, you can look for indicators that show it is expired.

Typical signs of expired gasoline include the formation of sediment or water in the fuel, and difficulty starting the engine. Expired gas will look muddier and have a darker color. Additionally, if you notice reduced engine power, knocking sounds, or increased emissions, it may indicate that the gasoline has gone bad.

Expired gasoline is a particular problem in vintage cars with carburetors and small engines that sit for a season. Many times when going to start them the next year, they will not start. There may not be a problem with the engine but bad fuel that no longer has the volatility to vaporize in a carburetor. Draining and filling with fresh fuel is the first place to start in this scenario. Many times fuel will oxidize in the carburetor as well and gum it up. Sometimes the carb needs to be removed and cleaned before fuel will properly flow again. Luckily most modern fuel-injected engines do not have oxidation issues, and the fuel will still flow even if its old.

carbureted engine with expired gas
Carbourated engines are much more susceptible to expired gasoline as they require high volatility to operate.

Can You Drive With Expired Gas?

Driving with expired gas can be risky and may lead to engine damage and reduced vehicle performance. Expired gasoline may have lower octane levels and could contain harmful contaminants, causing engine knocking, misfires, or stalling. Using expired fuel can lead to a decrease in the safety and reliability of your vehicle. Ultimately, it can result in costly repairs. If you suspect that your gasoline has gone bad, it’s best to avoid using it in your vehicle or equipment. Instead, safely dispose of it and refuel it with fresh gasoline.

Pro Tip: Does your vehicle use diesel? You’ll want to know What Temp Does Diesel Gel? How to Avoid Thickening Fuel.

Refilling gas tank
If your gas is going bad, top off with fresh immediately to dilute the lower quality fuel.

What to Do If Your Gas Expires

Before you decide what to do with your expired gasoline, you will want to first check how much is left in your tank or container and how old the gas is. Once you determine this, use the following steps to safely handle the expired gas.

Mix Old Gas With New

If your tank contains less than 50% of the old fuel, or if removing the old fuel is too challenging, mix fresh gasoline into the tank. After mixing, burn off at least half a tank of the fuel. After, refill the tank with new fuel to dilute the tank further and improve the overall fuel quality. 

Remove Expired Gas From Vehicle Or Tank

If your tank is over 50% full, or the vehicle won’t run at all, you will need to completely remove the old fuel. Identify the location of the fuel tank in your vehicle. For most vehicles, the fuel tank is under the rear of the car or under the trunk floor. If there is a fuel line connecting to the tank, you may need to disconnect it to drain the gas correctly. Siphoning or pumping the fuel out is another way to remove it. Many times the tank needs to be dropped and fully cleaned as well. We had to do this one time, and it was a lot of work.

fuel tank removed from vehicle to clean out bad gas
We once had to remove and clean our fuel tank, first, we had to drain it before dropping it.

Dispose of Expired Gas Properly 

Disposing of expired gasoline correctly is crucial. Contact your local hazardous waste center or relevant authorities to learn about the appropriate procedures for disposing of expired gas in your area. Never pour expired gasoline down the drain, on the ground, or into regular trash bins. It can pollute water sources and harm the environment.

Pro Tip: Don’t make an accidental gas faux pas. Find out Is It Illegal to Pump Gas With Your Car Running before you fill up.

What Is a Fuel Stabilizer?

Adding a fuel stabilizer to your gasoline can help extend the life of your fuel. Fuel stabilizer works by preventing or slowing down the oxidation and reactive processes, which is one of the primary causes of fuel degradation. Fuel stabilizers help create a protective barrier to maintain the fuel’s chemical composition.

STA-BIL Storage Fuel Stabilizer - Keeps Fuel Fresh...
  • Preserves Fuel - Keeps fuel fresh for up to 24 months so you can...
  • Prevents Corrosion - Maintains a healthy fuel system by ensuring...
  • Ensures Quick, Easy Starts - Helps you store any equipment or...

How Long Does Fuel Last With Stabilizer?

After mixing a fuel stabilizer into your gasoline, you can significantly extend the shelf life of your fuel. In optimal storage conditions, gasoline treated with a fuel stabilizer can last for up to two years or even longer without a significant decline in quality. This is a notable contrast to the three to six-month shelf life of untreated gasoline.

Adding fuel stabilizer to boat each fall
We add fuel stabilizers to our boats each year when we store them.

How Often Should You Add Fuel Stabilizer?

How often you should add a fuel stabilizer to your gasoline depends on your usage and storage patterns. If you regularly use up your gasoline within a few months, adding a fuel stabilizer with every fill-up is not necessary. However, if you plan to store gasoline for an extended period, it’s best to add a fuel stabilizer to every tank before storage. Manufacturers offer fuel stabilizers in various concentrations. Follow the instructions for the recommended dosage of fuel stabilizer for your fuel tank size and storage duration.

When To Use Fuel Stabilizer - Ace Hardware

Use Your Fuel Foresight to Protect Your Stored Engines

Nothing will ruin your road trip faster than engine damage from expired gas. Use your fuel foresight to ensure you don’t find yourself with smelly, sludgy gas in your vehicle. Whether you have a car sitting for an extended period in your garage or a container of gas in your shed, you want to ensure your fuel doesn’t expire. So if you plan on storing your gas and not using it right away, ensure you store it in optimal settings and add a fuel stabilizer to extend its shelf life. 

Have you ever had to dispose of expired gas? Tell us about your experience in the comments!

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About Tom Morton

Tom, a Pacific Northwest native, is our technical genius. Born in Washington and raised in Alaska before settling in Michigan. He's the man who keeps our operation running, both figuratively and literally.

With a background in Electrical Engineering, Tom specializes in RV solar systems and lithium batteries. He made history as the first documented individual to use a Tesla battery module as an RV battery. Tom has personally assisted countless RVers with system installations and has educated thousands more through his videos and articles.

Cinematography is another of Tom's passions, showcased in his work on the Go North series. You can see his camera skills on display in The RVers TV show on Discovery Channel and PBS where he also stars as a co-host.

Tom's mechanical expertise extends beyond RVs to boats, planes, and all things mechanical. He's renowned for taking on maintenance and repair projects single-handedly and is often spotted underneath RVs, making him the technical backbone of our endeavors.

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Sunday 3rd of September 2023

Just smelling gasoline can tell you its bad. If it smells like turpentine or paint thinner, its gone bad!