Does Premix Fuel Go Bad? HomeMade Vs Commercial Gas-Oil Mix

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Paul Brown

Paul has a two-acre yard on red clay soil in Southeast Texas. He knows exactly what the challenges are to nurturing a thriving yard in difficult soil.Paul takes a practical approach to yard improvement and enjoys putting best practices and “golden rules of lawn care” to the test.

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So you have a full tank of premix fuel that has been sitting on the shelf for quite a while. Are you wondering whether it has gone bad, or can you still use it successfully in your two-stroke? Let’s solve this!

Does premix gas go bad? Yes, premix gas can go bad. A homemade premix will only keep for up to two months at most. This is due to the oxidation and degradation of the gas. Commercial premixed fuels have unopened shelf lives up to 10 years and opened shelf lives of 2 years. 

Read on to get all the tips you need to maintain the proper functioning of the engine of your two-stroke equipment.

What Is Premix Fuel?

I’ve always thought of premix fuel as the commercial product that comes with the gas and oil already mixed.

But people use the term “premix” for both mix-it-yourself and store for later solutions as well as pre-manufactured mixtures. I want to make sure that I address both here so that you don’t walk away without the information you need.

And so, throughout this article, I’ll be identifying these so that you know which one we are talking about.

The two types of premix fuels are:

• DIY Premix – This is when you mix your own gas and oil for later use.
• Commercial Premix -These are the store-purchased premix fuel solutions offered by manufacturers such as Stihl, Trufuel, and Husqvarna.

I will address both but know this: commercial premixed fuel has a much longer storage life than a DIY premix. If you are mixing your own oil and gas solution you should not be storing it for more than a couple of months, ideally at least.

Shelf Life of Commercial Premix Fuels vs DIY Premix

So, how long is that mixed 2-stroke gas and oil good? Here’s an example of the shelf life of a couple of common commercial premix fuels designed for gas-powered 2-stroke yard tools against that DIY mix in your garage:

As you can see, the shelf life of commercial premix far exceeds DIY premix solutions.

I know it can be tempting to use an old DIY premixed fuel that’s been sitting your the garage but your yard tool’s engine and combustion system rely on the quality of the oil and fuel blend.

Why Does Home-Made Premix Gas Go Bad?

First, the quality and age of oil can impact the quality of the mix. If you have left the oil for the mixture open for several years (over 2), this can cause the premix to lose its viscosity and, therefore, its lubricative power.

Over time, heat, sudden changes in temperature, moisture, and water can compromise and damage the quality of the oil.

Even if you use new oil or oil that comes from a sealed container, your DIY premix does not have a long shelf life. This is especially true if using pump gas from your local fuel station.

Think about the shelf life for commercial premixed fuels and how it’s reduced when the fuel is opened. Here’s the key reason that a DIY premix goes bad faster than a commercial premix:

Home-made premix fuel goes bad quickly because gas from a fuel pump has already begun to degrade and oxidize. It is intended for immediate use. Commercial premix fuels come in containers that prevent oxidation and are designed to provide an extended shelf life of the gas.

If you are mixing a blend exclusively for your weed eater or leaf blower, you should keep in mind that their tank size is very small. To avoid wasting much of the DIY premix, you should only prepare the amount that you are sure to use in the next couple of weeks to one month.

Now, we all know that you can buy stabilizer solutions like Stabil to add to the premix. That is an option and it can extend your DIY premix’s shelf life to up to 12 months.

Is Premix Fuel Worth It?

Buying a commercial premix fuel is worth the cost to insure longer shelf life, precise mixture ratio, and engine warranty. Mixing fuel and gas yourself can result in inaccurate gas-to-oil ratios which can damage a 2 stroke engine over time.

When it comes right down to it, it is really difficult to recommend mixing your own oil and gas these days. Small engines depend on precise gas-to-oil mixtures. I get wanting to save money but at some point, it feels a little penny-wise and pound-foolish.

Now, if you are premixing fuels for a dirt bike and are burning through gallons at a time, then sure, it makes sense to mix your own. You just wouldn’t want to store it for too long at a time.

But if you are using premix fuels for yard tools, the tanks are usually small. And the mixture ratio really does matter. Adding a little too much oil will result in your weed eater smoking continuously and even in a clogged engine. Not enough oil can lead to an overheated engine that does not perform as well.

The peace of mind that comes from having a commercial premix that has an extended shelf life and precise mixture ratio far overshadows a few pennies in savings from a DIY solution.

Advantages of Commercial Premix Fuel

There are many advantages to commercially prepared premix fuels, some of which we’ve already outlined. But just to drive this point home, let me offer a little more information.

First and foremost, remember that with commercial premix fuels the gas/oil ratio calculation is clinical, and the manufacturers are often giants of the industry, such as Stihl, ECHO, and Trufuel.

There are many advantages to buying a ready-to-use premix such as:

• Save time and energy
• Help you prevent residue build-up in the engine
• They usually include high-octane, ethanol-free gas and high-quality oil, which helps them reduce smoke and run cleaner.
• They aim at increasing throttle performance and starting process.
• They include high-quality stabilizers that extend their shelf life.

One of the best characteristics of premixed gas/oil blends is that they last as long as stated by the manufacturers. No guessing!

How To Make DIY Premix Fuel

If you are dead-set on making your own premix, here are a few suggestions:

• Use fresh oil, A lot of websites recommend using oil that is fresher than four years if you kept it in a sealed container. Opened oil should be used within about 1 year or less. (I’d just use unopened).
• Only use oil that does not leave residues and is ashless to preserve the functioning of the engine. Follow your manufacturer’s guidelines!
• Use only fuel with less than 10% of ethanol. Ethanol will attract moisture and particles of water, which can, in turn, spoil the premix much quicker and cause tremendous problems with the engine. Click here to read about the dangers of ethanol on small engines. Very important!
• When preparing the mixture, you should first add half of the desired quantity of fuel into a non-spill, clean tank. Only after this step, you can add oil (source). End the procedure by filling the container with the rest of the fuel. Shake to have a uniform mixture.
• Ensure the tank you are using to store the premix is clean and free of debris that can represent a risk for the engine.
• Always keep the premix sealed and labeled.

Conclusion

While using an old container of DIY premix fuel that you found in your garage could be tempting, it’s not worth the risk to your 2-stroke engine.

You are better off mixing a new solution or buying a commercial premix fuel like Trufuel (link to Amazon). It can sit on a shelf unopened for years and will be waiting when you are ready.

For a complete comparison of popular premixed fuels, read Stihl Motomix vs Premixed Alternatives: 4 Products Compared.