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Should You Mix New Gasoline With Old?

The Truth About Mixing Old Gas With New

It’s always a good idea to keep extra gas on hand, especially if you want to be prepared. You never know when shortages, disasters, or other events will cut off your access to the pump. But a big problem with gasoline compared to other types of fuel is it tends to go bad pretty quickly.

But gas can get old and stale before it goes truly bad, and some folks say that you can mix this older gas with new gas to bring it back to life. Great if it will work, but it sounds too good to be true. What’s the truth? Is mixing old gas with new a good idea or not?

Yes, it is possible to mix old gas with new, fresh gas in order to use it up as long as the old supply has not gone truly bad.

The Old Trick That Works

Turns out this is one old trick that has been around for a long time. But as you might expect it is entirely possible that your old gas can be too far gone to be salvageable, and mixing it with your new stuff is only going to ruin the new and you’ll still be wasting the old.

It’s a fairly simple process, but there’s a lot you’ll want to know, so keep reading…

Understanding Gasoline Breakdown

Maybe, maybe not. Gasoline breaks down in time, and depending on the exact type and the blend it will break down a lot sooner rather than later.

For all types of gasoline, this is because oxidation starts to deactivate the volatile compounds that give gasoline its functional properties.

Harmful byproducts can also begin to form in the gas that can damage an engine, too. In the case of ethanol blends, which constitute most types of consumer-grade gas you’ll get these days, the ethanol and gas mixture will begin to separate, a process called phasic separation.

But the end result is ultimately the same: the older the gas gets, it loses ever more efficiency, becomes less reliable, and eventually will fail to function an engine entirely- or even cause damage!

Determining When Gas is Too Old

This depends on the blend. Most ethanol-gasoline blends are in very bad shape by about 3 months or so. Most of these blends even start degrading significantly within just 30 days.

However, some long-life gasolines or pure gasoline blends will be good for 6 months or even significantly longer.

The most important thing you can do is it keep an eye on the gas and inspect it for signs of degradation. Knowing what to look for, and with a little experience, you’ll be able to tell when your gas is a little old, pretty stale or when it is truly bad. Look for the following symptoms of degradation with age, and keep in mind gas can exhibit one or multiple:

  • A distinct layered look akin to oil on water
  • Significant darkening of the gas
  • A reddish hue starting to develop
  • Slime or particulates floating in it
  • Peculiar odors when you crack the seal on the container.

Gas that is going stale but is still usable will usually darken just a little, but that should be the only thing that you notice something off about it.

Does Gas Go Bad Sitting in a Fuel Tank?

Yes, it does. Gasoline can go bad sitting in any kind of container, be it an approved fuel container or the gas tank of a vehicle or tool.

Basically, the chemical processes that cause gasoline to go bad will occur no matter what, and the more air that can reach the gasoline the faster this will happen although it isn’t strictly necessary for it to become stale and then break down.

Regardless of how the gasoline is stored, or what it is stored in, you’ve got to have a plan for using it in time or reconditioning it with fresh stuff.

The Consequences of Using Bad Gas

It depends on how bad the gasoline is and how sensitive the engine is.

Gas that is a little stale and when it loses combustibility, it will usually run a little bit rougher and sometimes turn on a check engine light in a car.

Gas that’s seriously old might fail to start at all, and gas that is well and truly bad, full of nasty deposits, could clog up fuel lines and filters, injectors, and cause other havoc that can mean costly repairs.

This is why you must be so cautious about using old gas; take care in determining if the waste is worth the potential heartache and hassle.

The Benefits of Mixing Old Gas with New

Mixing in new, fresh gasoline with old gas will help rejuvenate the older fuel because it in essence replenishes the combustible compounds necessary to make it function in an engine. If you want to look at it a different way, it cuts the worn-out, harmful compounds in the old gas.

Either way, it creates a blend that is capable of working and can be a good method of using up old supplies that aren’t too far gone.

When You Shouldn't Mix Old and New Gas

No, not necessarily. As mentioned, it is entirely possible that very old fuel is just beyond saving. Worse, aside from being unable to bring it back to life and use it up, adding new gasoline can severely contaminate it and cause it to fail or damage your engine!

You should only add new gasoline to older gas that is a little bit stale. If it is darker in color or showing slight signs of separation, you should be able to rescue it by mixing the two together.

The Right Way to Mix New Gas with Old

If your old supply isn’t too far gone and you’ve got some new you’re willing to mix with it, and you don’t mind the risk of a potential malfunction concerning your engine, all you need to do is mix the old stuff with the new gas in a one-to-one ratio if the old gas is just a little stale.

If you’re dealing with very old gasoline that isn’t totally broken down or separated, you’ll need to use more fresh gas in the mixture. A three-to-one or even four-to-one ratio might be needed for very old fuel.


By: Tim Makay
Title: Should You Mix New Gasoline With Old?
Sourced From:
Published Date: Tue, 12 Dec 2023 11:08:19 +0000

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