How to Rejuvenate Old Gasoline by Yourself

Gasoline storage is a big deal for preppers, since you’re going to need plenty of it to run both your vehicle, your generator if you have one, and all your gas-powered tools after commerce grinds to a halt and supply lines collapse in a SHTF situation.

red 10 liter Jerry petrol can
red 10-liter Jerry petrol can

There’s just one problem that crops up constantly with long-term storage of gasoline, namely that modern gasoline breaks down and loses potency over time, meaning all your careful investment in both the gasoline and in the needed containers to store it goes to waste!

If you don’t use it, you lose it! Or do you? …

There are no two ways about… Older gasoline is liable to run poorly in an engine, or even fail to run it at all. Gasoline that is way past its “good” date can also potentially damage or destroy fuel system components, and leave harmful deposits.

These are things you have to think about and risks you might have to take when your choice is old gas or no gas at all. It is easy to believe that you just have to pour it in and take your chances.

Except you don’t. No matter if you’re dealing with known-quantity gas that is simply a few months past its date or found gas of unknown vintage, there is a way to bring it back to life and make it usable.

In a nutshell, the way you rejuvenate old gasoline is you mix it with new gasoline in a 3 to 1 ratio (new to old gasoline), and then add some octane booster or detergent additive.

This will stretch your supplies, and also hopefully prevent damage and unnecessary wear on the machine you’re fueling with it. In this article, I’ll tell you what to do…

Gasoline Gets Old?

Yes, yes it does. And in fact, it can go bad in a couple of different ways…

Depending on what type of gasoline you have, either pure gasoline or an ethanol-gasoline blend, your fuel can give up the ghost in a couple of ways: either by losing its combustive properties due to oxidation over time, or by separating into its constituent gasoline and ethanol components.

Either will mean your gas no longer combusts properly, or at all. Add in contamination by ever-present moisture, and the clock starts ticking on your gasoline as soon as you store it.

If you have the altogether too common ethanol-blend gasoline that is sold at the vast majority of gas stations in the United States, you only have about three months’ worth of storage time before the ethanol itself separates from the gasoline.

Ethanol-blended gas is especially insidious for preppers trying to store it long term because as the ethanol separates it will absorb a considerable amount of water, which it loves, being hydrophilic.

As you are probably thinking, this is a literal non-starter, and will render the fuel completely unusable as the mixture is now contaminated by water.

Pure gasoline, if you can find it, will last significantly longer, usually around 5 or 6 months, but it too will eventually fail in its old age, this time due to the volatile compounds breaking down at the molecular level. This results in a falling octane rating until eventually, it will not combust at all.

So no matter what kind of gasoline you have taken pains to store, it will eventually get old, and go bad one way or the other.

This means you either need to use the supply in the allotted period of time before it loses its “pop” or barring that come up with some way to get the old gas turning the motor over again.

Luckily, we can take care of the latter under certain circumstances. But you have to be sure of what kind of gas you are dealing with before you try!

Is it Just Old, or Has it Gone Truly Bad?

Before we get to the actual process of reconditioning old gasoline, there is one thing you must learn and always be certain to check for before attempting this procedure.

I’m not trying to hold you up from getting to the information you opened this article to learn, but this is essential in order to avoid wasting gasoline, and potentially ruining your engine so we have to talk about this now.

Gasoline can get old, and gasoline can go truly bad. There is a difference; it is possible to save old gas, but you cannot save gasoline that has gone bad due to contamination or phasic separation in the case of ethanol blend gasoline.

How can you tell the difference? If you know you are dealing with ethanol-blended gasoline that is older than about three months, I wouldn’t even try to recondition it.

But in case you want to assess its state or just compare another source of gas against known good gasoline, all you will need is two clear glass vessels to hold a sample of each. Once you have obtained samples, compare them side-by-side.

How can I tell old gasoline from fresh gasoline

Old Gas – Can Be Reconditioned: If your gasoline is uncontaminated but is instead just old, it will still appear clear, just slightly darker than the newer gasoline. This is the gasoline that you should be able to recondition.

Note that the darker or “redder” the gas looks, the more the components have started to turn into a varnish or lacquer-like substance. This can gum up your engine even if it still runs it!

Very Old Gas – Cannot Be Reconditioned: If your gasoline looks cloudy, murky, or milky, or it has noticeable sediment or silt floating through it is definitely no good and you shouldn’t even try to recondition it.

A sludgy, slimy or waxy appearance is also an obvious indicator that the gas is beyond saving.

Phasic Separation – Cannot Be Reconditioned: For ethanol-gas blends, if you notice obvious layers in the sample you drew from the suspect gas, akin to oil floating on water or two or more distinct color bands in the sample, it has already undergone phasic separation and is very likely contaminated with water.

Unsalvageable in all cases. Throw it out!

What Will Old Gas Do to an Engine?

Old gas is no good for engines of any kind. At best, you can expect sputtering or engine knock. At worst, it will gum up fuel injectors, causing them to fail and potentially cause serious, long-term engine damage.

This is why it is so critical to recondition gasoline (if it can be saved) or dispose of it properly once it has sat too long in storage.

Reconditioning Old Gas Yourself

Assuming the gasoline you have is just old, not contaminated as described above, there is a highly intricate, precise and advanced scientific method for bringing that gasoline back to life.

I expect you will probably need to copy and paste the procedure for later study. Are you ready? To bring your old gasoline back to life you need to do the following:

  1. Add to it fresh, good gasoline in a 3:1 ratio. For very old gas the ratio is 4:1 new gas to old.
  2. You can add directly to the gas tank if you have about a half-tank of gas. If you are mixing in the tank and have a full or nearly full tank of old gas, you’ll need to drain some off to make room for the mix.
  3. Shake container or rock vehicle slightly to mix well.
  4. Add detergent additive (if required, see below).
  5. Try to start engine. Expect it to take a few tries.

You read that right. That’s it. No, that’s really it. Okay, there is a little bit more to it than that, so I’ll explain.

The reason why mixing new or at least functional gasoline into old stuff works is because you are replenishing the combustive elements in the “old” when you form a solution from the two.

This isn’t easy for a layperson to understand, because the science behind it is surprisingly complicated.

As it turns out, gasoline is actually pretty complicated to make on an industrial scale. It definitely isn’t crude oil that’s been pulled from the ground and run through a couple of filters.

This stuff has to go through several stages of refinement, and each one must be conducted under carefully controlled and monitored conditions.

Gasoline is a petroleum distillate, not straight petroleum, and the very fact that it is a highly volatile distillate means that, over time, the molecules responsible for that peppy combustion break down and as a result the gasoline loses potency, lowering its octane.

When you mix in new gas you’re putting some of those combustive elements back into the mixture.

Now, the resulting blend will have lower octane overall than the new gas you are adding (because you are in essence diluting it) but the result is gas that, while it might run a little rough, will indeed run most engines so long as it is within a few points of the mandated octane rating for the engine.

Obviously, you should not try this if you are trying to fuel up some fancy, super-tuned, and high-performance engine unless you are truly desperate.

What About Diesel Fuel?

Most diesel fuel blends have a much longer shelf life than comparable gasoline, but they are still mixed with all kinds of additives from the manufacturer that will cause problems for very long-term storage.

The primary concern with long-term diesel fuel storage is water contamination, which will cause bacteria and other microorganisms to grow in the fuel in a sort of algae-like raft, causing clogged filters and eventually leading to engine failure.

Reconditioning diesel fuel is possible, but is a totally different process from gasoline and is beyond the confines of this article.

What About Re-Conditioner Additives?

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Fuel additives of all kinds are popular for various reasons. From octane boosters to fuel system cleaners, not the least of which are long-life fuel stabilizer additives, these can extend the shelf life of the gasoline you plan on stashing.

Old standbys like Sta-Bil really do work, though you have to get them as gasoline or ethanol-blend-specific products, and they can only halt further degradation.

These handy concoctions can extend the shelf life of your gasoline by anywhere from 3 months all the way up to 12 whole additional months. That is impressive, and a perk that all preppers should consider!

Unfortunately, shelf-life additives do nothing to bring old gas back to life. They definitely will not bring separated or contaminated gas back to life.

Stale Gas: Can it be treated with additives? My unscientific test and results.

Additionally, they only work as advertised when added to gasoline when it is at its freshest by arresting the infiltration of water and the molecular breakdown of the gas we discussed previously.

But that brings us to some additives that their manufacturers claim can restore old, worthless gasoline to peak or near-peak efficiency. Unfortunately, these bottles do not work the way they are described.

If you care to consult what ingredient lists are available to the consumer, you’ll see that many of these are only petroleum distillates. There is no secret sauce or magic ingredient that can transmogrify old broken-down gasoline into fresh, peppy new gasoline.

At best, you are getting an “octane shot” akin to what will be accomplished by adding fresh gasoline to the old as I described above but are now dealing with a mixture that will not have its heavier chemical elements at least halfway properly incorporated with the lighter ones. At worst, nothing will happen.

It turns out that gasoline that has gotten too old is either lost permanently if it is an ethanol gasoline blend, or can only be reconditioned to a useful state by adding a quantity of newer, usable gas.

Detergent Additives Can Help Your Engine Cope with Old Gas

There is another category of fuel additive that can come in really handy if you are forced to use pretty old gas that is on the verge of going truly bad.

As detailed above, when you have gas that is turning dark or reddish but has not yet gone murky or cloudy, it may work but the polymerization of the compounds in this old gas can coat and clog critical engine components. Not good!

However, you can prevent the worst of such harm with a detergent additive in the mixture. These are common, effective, and cheap, but don’t get taken by snake oil claims and fancy marketing.

All you need to do is look for a detergent additive that has PEA or PIB detergents and add it to your blended gas according to the package instructions.

It will scour these deposits from affected engine components before they cool and the deposits harden.

Consider the Use of Long-Storage Fuel

One way to recondition old gasoline is to avoid having to recondition it in the first place! Okay, I am being a bit cheeky, but hear me out as I would be remiss if I did not mention this.

There exist manufacturers of gasoline who specialize in producing gasoline blends in various octanes that are optimized, from the refinery, for a long shelf-life, as much as one or two years, adding not one single thing to it on your part!

That is an exceptionally long-lived gasoline by anyone’s standards, and even better, it can be had in either leaded or unleaded variations along with other specific characteristics to meet any purpose.

All you’ll need to do is perform a search for suppliers of this gasoline in your area and find who they sell it to or where you can go to pick up a quantity from the maker directly.

Combining this gasoline with a ventless container that will prevent contamination of water will give you excellent shelf life and greatly simplify the task of stockpiling gasoline among all your other preps.

Note that this gasoline is significantly more expensive than conventional out-of-the-pump gas you would get from the corner station, but considering you are purchasing it for a rainy day and not for daily driving, it is well worth the investment.

Frequently Asked Questions

How Old is Too Old for Reconditioning Gasoline?

The storage life for gasoline depends on many factors, including its blend, container, ambient conditions, and more. But generally, ethanol-gas that has gone for 6 months is totally gone, and pure gas that is a year old is beyond saving unless it is a special long-life type.

Can Old Gasoline Ruin an Engine?

It can. Old gasoline that remains combustive enough to function can leave behind hard, lacquer-like deposits in an engine that will impair its efficiency or cause malfunction, maybe preventing it from working at all.

Can You Filter Gas to Remove Sediment?

Yes, though you need to do so carefully. Old gas that has started to separate and gum up will not be saved by filtration. But if you have fresh good gas that accidentally gets contaminated with dirt or other debris you can filter it to remove it.

What about Additives that Claim to Fix Phasic Separation?

Total bunk. No additive is going to save ethanol-gas that has separated. All such claims to the contrary are, for now, false. These additives may work to stabilize ethanol-gas and prevent separation for a time, but they will not restore it to working condition.

Can You Recondition Gasoline with Oil Additives for Lawn Mowers, Power Tools, Etc.?

Possibly. The presence of fuel oil is another wrinkle in the mix. You’ll need to consult the manufacturer of the fuel oil to know for sure, but in a pinch, you can add new gas with oil to the old stuff in a 1:1 ratio as above, so long as it is not showing any signs of being too far gone.


Older gasoline, so long as it is pure gasoline and not an ethanol-gasoline blend, can be successfully restored to life by mixing in an equal quantity of new, fresh gasoline.

While this does reduce the overall octane rating it will bring the gasoline back to life and make it usable in most engines, even if it does introduce rough running or idling. This is a great way to stretch what gasoline you have if you suspect it is past its useful life.

Make sure you never try this with contaminated gas or gas that shows obvious signs of separation, and if in doubt never risk your engine or generator using old gasoline if new is available.

reconditioning gasoline Pinterest image

4 thoughts on “How to Rejuvenate Old Gasoline by Yourself”

  1. Hello,
    I’ve look everywhere on-line, without luck, for long term gasoline that can be bought at a gas station.
    What is it called? Can it be found commonly in California? Is there a minimum purchase amount? What is the going price per gallon?

    1. Here in Florida it’s called “Rec” for recreational – meant for items that aren’t daily use. I can find it at some Marathon gas stations. Ours is 90 octane — “rec 90”. If you can’t find it, try talking to a marina / boathouse staff person. The boat gas should be ethanol-free for the same reasons, but beware you never know with Cali lawmakers.

  2. Has anyone ever tried distilling old gasoline? Hard alcohol is distilled mash, eg wine, beer something fermented. So could the same process be used on old gasoline? Using a hot plate or crockpot and a “worm”, evaporate the old gas and collect the condensate. I’ve got about 70 gallons of old gas that I don’t want to throw away and am thinking of ways to reuse it

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