Can I mix old gas with new gas?

Wondering if the good ol’ (quasi-Biblical) advice “and no man mixeth new gas with old gas” is correct? If so, you’re not alone in those thoughts. According to Google, many people pose the question of mixing old and fresh gasoline. There’s a good number of folks typing “Can I mix old gas with new gas” into their favorite search engine.

Also, there are many gas-related questions one might pose. Still, the answer to the one in the title of this article makes us ask more. For instance, let’s say the answer is: absolutely no. We could ask: what’s so wrong with bad gasoline? Or: Is it a health hazard, and is there a way to somehow rejuvenate it? Luckily, we’re here to tell you all about it in the text you’ll find below!

Yes, it’s possible to mix old gas with new gas. Just make sure you’re adding just a tiny bit of old gas into the mixture. Also, avoid running your brand new car using the aforementioned combination. For instance, use it with your lawnmower or old car. Lastly, avoid mixing old gas that smells a bit like old paint thinner.

There’s much more from where that came from! Stick around!

Table of Contents

Wait, gas can go bad?

That’s right, gasoline is bound to go bad after a certain period of time. Whether it’s inside your vehicle’s tank or in storage – it doesn’t matter. Also, even if you store it properly – it can’t stay forever in your shed. It has its own shelf life, so to speak.

Over time, gasoline degrades and loses its combustibility. It happens as a result of two processes: oxidation and evaporation.

Okay, and how long can it last before spoiling?

Yeah, about the expiration date… Well, it depends on the type of gasoline we’re talking about. Anyway, the following stands only for gasoline that’s properly stored. Depending on their shelf life, we can differentiate between three types of gas:

  • Pure gasoline. This one will last you anywhere from three to six months.
  • Ethanol-blended gasoline. Unfortunately, this type has a much shorter shelf life. It will last ya from two to three months in total.
  • Fuel-stabilized gasoline. Adding a stabilizer will expand the shelf life of your gasoline from one to three years.

Keep in mind this only stands for properly stored gasoline. Oh, and we almost forgot: your vehicle’s tank is far from being the ideal storage area. If your car sits still for about a month, it’s safe to assume the gas inside it has gone bad. This shouldn’t mean you’re not allowed to drive the vehicle with month-old gas. It just won’t perform so well. Lastly, avoid running your car on gas that’s been sitting for more than six months.

Wondering how to notice if your gasoline’s gone bad? If so, feel free to check out this page.

Time isn’t your only enemy

Besides aging, there’s another way your gasoline can spoil. Water’s your enemy, too! If water happens to find a way into your gas tank… Yup, that’s right! It will contaminate your gas. Also, there’ve been situations in which water came straight from the gas pump. Still, that happens once in every second lifetime, if ever.

Anything else?

As a matter of fact, yes. A broken/cracked fuel line might cause your gasoline to spoil. Also, the flakes in your tank aren’t to be messed around with!

Is it true that bad gasoline can ruin your engine?

If you’re wondering if bad gas can do some damage to your car, the answer’s: maybe. What do we mean by this? Well, maybe means that it’s possible it can happen. Still, it’s not something you’d wanna call the usual stuff.

If it does some damage to your vehicle, the internal engine components will take the blow. Also, bad gasoline might form a gum residue causing blockages. If you’re using ethanol-blended gas, it may draw water vapor straight into your fuel line. That might cause internal corrosion.

Okay, so that’s about it for this “brief” introduction. We won’t keep you anxious anymore! Let’s check out whether or not it’s possible to mix old gas with new gas.

A fuel filler neck on a grey sports car.

Can you mix old gas with new gas?

Now, let’s put it simply: it’s possible to mix old gas with new gas. However, the simplicity stops right there. In other words: you’ll need to consider a lot of things if you’re planning to use the mixture.

What’s the ideal ratio?

First things first, let’s get something out of the way. It is absolutely not recommended for a person to mix a little fresh and plenty of bad gas. Also, it’s not recommended you sip whatever old+new gasoline mixture in your new vehicle. Even if it’s just a tiny bit of old gasoline in it.

Let’s try it like this. Imagine you’ve got some old gasoline left in your shed. The ideal thing to do then is to dispose of it safely. One of the ways you can safely get rid of it is to mix it with fresh gas. But have in mind: in the mixture, there needs to be just a little of it. 

What will you run on the mixture?

As we already said, completely avoid putting the mixture in your brand new car (under warranty). You can run your lawnmower on it. Also, it might be an old car or a truck you’ll want to use it with. There’s a ninety-nine percent chance they’ll run just fine on your gasoline mix.

Now, if you notice your old gasoline smells too funky, then… Well, it means you should forget about mixing it with fresh gasoline. The smell will most probably remind you of an old paint thinner. There’s your sign!

What to do if there’s bad gas in your tank already?

It’s simple! Well, to a certain degree… Anyway, you’ll want to drain the gas tank and blow out the fuel lines, if possible. You can only expect bad results if you try adding fresh gas to really dated gas in your tank.

What if you don’t have the option to drain the tank and lines (it’s plenty of work)? Disconnect the gas lines under your car’s hood. Run the fuel pump, and you’ll pump almost all the age-old gasoline. Just a tiny bit will remain in the tank. Afterward, just put in a gallon or two of new gasoline, and pump it through the lines too.

Now that we’ve got that one cleared up, let’s see if there’s a way to rejuvenate old gasoline!

How to rejuvenate old gasoline?

First, consider why you want to rejuvenate old gas. If you’ve got plenty of old gas left then it’s alright. You’ll have a good motive to go through the process. On the other hand, if it’s a little old gasoline we’re talking about… Yup, you might want to throw it away.

Another thing: you’ll need to think about just for how long was your gasoline stored. If your gasoline is older than two years, it’s probably beyond your power to rejuvenate it.

Here we’ll show you how to rejuvenate (old) gasoline. In accordance with how the gasoline was contaminated, here’s what you can do:

  • It’s possible to filter the gas that’s begun to gum. This process will erase the build-up within the gasoline. Also, this will prevent the clogging of your lines.
  • You can simply decontaminate smaller amounts of old gas by hand. Just sip the water-polluted gasoline into a jar. Let the water settle down on the bottom of it. That will happen after 20 minutes or a bit more. Afterward, pour the top layer of gas into a different container. 
  • Larger amounts of water-polluted gas need special attention. There are products on the market that will help you leech the water out. They’re a solution if you’re not willing to separate smaller quantities by hand. 
  • The gasoline blends and additives can detach into layers that don’t mix. You’ll need to replace the evaporated hydrocarbons. Commercially available fuel additives will make the layers mix, restoring the gasoline to its previous state. 

Bonus tip: Can bad gasoline dissolve plastic containers?

To put it simply: gasoline, whether bad or good, will dissolve most plastic containers. That’s because certain types of plastic have a similar chemical composition as gasoline. Like dissolves like, as some folks would say. Anyway, there are types of plastic designed carefully for gasoline storage.

HDPE to the rescue

Ever heard about HDPE? It’s short for High-Density PolyEthylene. It’s the type of high-quality plastic safe gasoline containers are made from. Avoid strong your gas in non-HDPE plastic containers. Milk jugs or ordinary plastic bottles are a big no-no!

Final words

That’s about it when it comes to mixing old and new gas, dear folks! Hopefully, you’ve enjoyed reading this one as much as the last! Also, we hope you’ll find it pretty useful when the time comes.

For more gasoline-related tips, don’t hesitate to jump in here.