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Does Gasoline Go Bad? Don’t Find Out the Hard Way!

Does Gasoline Go Bad? Don’t Find Out the Hard Way!

While it may seem trivial to some, the question “Does gasoline go bad?” is actually a pretty important one. If you store your RV for long periods of time, for instance, the answer to this question may be critical.

In fact, if you use gasoline for anything – a car, a generator, a lawn mower or any small engine – or if you have a gas-powered motorhome, today’s topic is for you. 

And if you’ve got some gasoline sitting in a gas tank in your garage, you need to understand its shelf life before you pour it into a small engine or your car’s tank.

That’s why we’re dedicating today’s post to answering the question of how long gas lasts and why.

Does Gasoline Go Bad?

In a word… yes! Gasoline does, indeed, go bad.

But the more pertinent question is “WHEN does gasoline go bad?” In other words, how long does it take for gasoline to go bad?

This question is a bit more complicated to answer because there’s no set time it takes for gasoline to go bad. There are multiple events that can influence the amount of time it takes before gas goes bad.

Some of the factors that come into play include how you store the gasoline, whether you’ve used fuel stabilizers, the time of year, and the percent of ethanol contained in the gas. (More than 98% of gasoline in the United States is an ethanol blend, typically E10 which is 90% gasoline and 10% ethanol.)

But generally speaking, properly stored gas is good for about 3-6 months.

What Influences the Time It Takes for Gas to Go Bad?

It’s important to understand the conditions that can shorten or lengthen the time it takes for gas to go bad.

For example, gas in the tank of your RV or car can start to degrade in about a month. However, under optimal conditions using a fuel stabilizer like this one can potentially extend the shelf life of fresh gas for a year or even more.

STA-BIL Storage Fuel Stabilizer - Keeps Fuel Fresh For Up To Two Years, Effective In All Gasoline Including All Ethanol Blended Fuels, For Quick, Easy Starts, Treats Up To 80 Gallons, 32oz (22214) , Red
  • STORAGE – STA-BIL Storage Fuel Stabilizer eliminates the need to drain fuel and keeps gasoline fresh for up to 24 months. Never fear your car or...
  • ENSURES QUICK, EASY STARTS – Treating your gas with this fuel stabilizer prevents gum, varnish, rust, and corrosion in your fuel tank, all of which...

The three greatest influences on the degrading of fresh fuel (gasoline) are:

Water

Earlier we mentioned the typical 90/10 ethanol blend found at 98% of gas stations in the United States.

Well, ethanol attracts water molecules which shortens the shelf life of gasoline. The more ethanol there is in your fuel, the faster that fuel will degrade and expire.

Evaporation

Gas is made of hydrocarbons, and some weigh less than others. In the heat of summer, lighter hydrocarbon molecules evaporate. That’s why summer fuel blends contain heavier hydrocarbons.

Likewise, winter fuel blends have lighter hydrocarbons so that in the cold temperatures your engine can run smoothly. This makes starting your car or RV easier and allows your entire fuel system to run more smoothly.

This is important because evaporation leads to oxidation. 

Speaking of which…

Oxidation

Oxygen is one of the main parts of combustion, but it leads to oxidation. Oxidation causes less effective and less efficient combustion over time.

Is It Okay to Use Old Gas?

Not if you want to keep your rig or vehicle in good shape.

Old gasoline can, at a minimum, decrease your car’s overall performance and result in lower fuel economy. But gas that’s a year or more old can cause more serious problems like engine knocking, sputtering, and clogged injectors.

Gasoline is a mixture of volatile compounds. As it degrades, it starts to solidify and become gummy. As that gummy substance moves into your engine it can clog filters, damage the fuel pump, gum up the lines, and damage a number of engine components.

In the end, it’s far less expensive to buy new gasoline than it is to deal with the consequences when you see that “check engine” light come on!

A "check engine" light illuminated on the dash of a vehicle

It’s best to be pre-emptive when dealing with gasoline. Either treat the gas with a high-quality stabilizer when it’s fresh (before you store it) or simply buy new gas. Don’t wait to see your “check engine” light illuminated to find out if you’ve done damage to your engine.

How Do I Know if Gasoline Has Gone Bad?

Expired gas tends to be darker in color than fresh gas (assuming you can see it in your tank). It also develops a sour smell (which may be easier to detect, just by opening the filler door/cap).

With that said, it’s always best and easiest to clearly label any stored gas with the date.

How Can I Prevent Gasoline From Going Bad? 

If you have an engine you don’t use frequently (a lawn mower is a good example), try to find a source of ethanol-free gas or at least a low-ethanol blend.

If you need to store gasoline in a container, be sure to use only a gasoline-approved container that is clean and airtight. Store the container at room temperature or in a cool area.

If you plan to store your RV or another vehicle for a period of time, consider using a fuel stabilizer. There are several on the market.

The product we mentioned earlier in the post (which we’ll link to again below) uses additives that are capable of preserving the gas in your engine or generator for up to 24 months. Frequently used in stored vehicles, generators, and boats, it prevents gumming, rust, corrosion, and varnish that can cause very expensive issues.

Use the product only with fresh fuel and keep your gas tank 95% full to avoid condensation build-up during storage.

Be sure to run your engine for about five minutes or so after adding this product (or any fuel stabilizer) to your tank so that it can treat the entire fuel system.

STA-BIL Storage Fuel Stabilizer - Keeps Fuel Fresh For Up To Two Years, Effective In All Gasoline Including All Ethanol Blended Fuels, For Quick, Easy Starts, Treats Up To 80 Gallons, 32oz (22214) , Red
  • STORAGE – STA-BIL Storage Fuel Stabilizer eliminates the need to drain fuel and keeps gasoline fresh for up to 24 months. Never fear your car or...
  • ENSURES QUICK, EASY STARTS – Treating your gas with this fuel stabilizer prevents gum, varnish, rust, and corrosion in your fuel tank, all of which...

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Mot

Wednesday 5th of October 2022

How do we get rid of old gasoline?

TheRVgeeks

Friday 7th of October 2022

Rules vary by local ordinance, so you’re best off checking with what the rules are in your area. You’ll need a safe container to transport it and will most likely have to drop it off at a waste disposal facility (like you’d have to do with left over paint or other potentially toxic household chemicals).

TJL

Saturday 17th of September 2022

My experience with my home generator is very similar to that of Mike (8/17/22). $500 for a new engine that had less than 100 hours on it. I use the generator rarely, but want it always ready to go. Therefore, I buy non-ethanol gasoline, at a premium of about $1/gallon, and add Sta-Bil. I also exercise it about 20 minutes a month and always use the fuel shut-off valve to run the gas out of the carb and engine. So far it has been flawless. Fortunately, My RV generator is LP and after 9 seasons with under 50 hours, that has also been flawless.

Michael Nistler

Saturday 17th of September 2022

Many thanks for the thoughtful article! And here in California, here's another reason why our gas containers are sealed. "Evaporative emissions are minimized or eliminated through the implementation of low permeation plastics and automatic sealing nozzles. Because of their large numbers, Portable Fuel Containers have the potential to create substantial hydrocarbon emissions resulting in ozone-forming smog and health related problems. As of July 1, 2007, all PFCs sold in California must be certified by the California Air Resources Board as meeting the low-emission requirements."

Fortunately our Onan generator runs on Propane, yet as a backup I have a 2K Honda gas generator and definitely use StaBil. Meanwhile, I have no idea if our diesel MBZ Sprinter would suffer if not being run each month but with the current diesel prices...

Happy trails, Michael and Grace

TheRVgeeks

Tuesday 20th of September 2022

Hi Michael. Thanks for that information. California is almost always ahead-of-the-curve on emissions issues… but the rest of the country almost always follows! 😉 As for diesel? Check out our article: https://www.thervgeeks.com/does-diesel-go-bad/

Larry Lee

Saturday 17th of September 2022

I have had good luck (if there is such a thing?) using Stabil.

TheRVgeeks

Tuesday 20th of September 2022

Glad to hear that, Larry.

Mike

Saturday 17th of September 2022

The biggest issue we've had with "bad" gas is with our generator.

If you are running an ethanol-gas mix and let the generator sit, the gas will gum up your generator pretty quickly. We learned the hard way that you have to run that generator for at least an hour every month to keep it clean.

We eventually installed a valve to shut off gas to the generator when we stored it. Shutting the valve and running the generator until it was out of gas made a big difference.

We use SeaFoam as an additive to keep the gas fresh during storage.

TheRVgeeks

Tuesday 20th of September 2022

Thanks for sharing that, Mike… great advice! Sounds like that shutoff valve is a simple, but elegant, solution!

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