Does fuel go bad and should you stockpile it?

fuel it a good idea

Considering fuel is proper cheap at the moment, we look at whether you should stockpile some fuel, or whether it’s better to just enjoy the price drop.

Considering we’ve not seen fuel this cheap since Netscape was the browser of choice (I mean, 79 cents a litre. Go forth and buy all the fuel), the question keeps coming up online, should we be stockpiling a bit of fuel at home while it’s cheap, and does it go bad?

We thought it was time to sit down and go through the ins and outs of storing fuel, how long it can last before going ‘off’ and working out whether you should actually stockpile fuel at home. Unfortunately, there is no short answer, so strap in.

Why does fuel go bad?

Over and above crude oil, petrol is highly refined to develop certain characteristics and volatility. The term volatility is used to describe how easily the fuel vaporises, and thus, is burnt in an engine. Worth mentioning is that regardless of whether within an engine, or getting the winter bonfire going (don’t do this), it’s not the liquid petrol that’s burning but the vaporised gas it emits.

Where this comes into play on fuel going bad, is that over time the more volatile components in fuel, tend to evaporate. As this happens, the overall volatility and ability to generate explosive force within an internal combustion engine diminishes. Sure, it will still be enough to start and run your average vehicle, but not nearly as well or efficiently as new, fresh fuel will. While not a perfect analogy, think of fuel losing its volatility over time like the RON rating of fuel; Say you stockpile some 91 Octane fuel for six months, when you retest that fuel, it may be down to say 75, or even 50 Octane, as the more volatile components within the fuel have vaporised off. So yes, your car will probably run on it, but not exceptionally well – That said, depending on what vehicle you have, how it’s tuned and the octane level it needs, you may well damage your engine by running older (and let’s say lower octane) fuel.

But, that’s not even the worst part. As with just about everything to do with anything automotive, oxidation is the true killer. Exposure to oxygen will cause the chemical composition of fuel to change. This will lead to gum and varnish deposits within your entire fuel system, or the jerry can it’s been stored in. These gum and varnish deposits will clog up and damage fuel lines, filters, and just about any other small and delicate area inside your engine. Anyone who has had to pull apart a carburettor from an engine that’s been sitting a while will know all about the gum and sludge that stagnant fuel will develop when being allowed to mix with oxygen over a long period of time. This also translates to newer vehicles with injectors and fuel lines becoming clogged with varnish and gum from older fuel.

Then of course, there’s water contamination. This is especially true when your fuel tank will cycle from hot to cold over a day, every day. This is especially true with ethanol blended fuel, like E10-E85. Ethanol is hygroscopic, which means it will absorb water (or moisture) from surrounding air. So if you leave the lid off a fuel container, or your fuel tank, or take the lid off and on frequently, it will allow more water to enter via the air, which will increase the water content within the fuel, along with the oxidisation issues we mentioned earlier.

Is there a way to tell if fuel is bad?

There certainly is, in that your fuel that’s been stockpiled for a while will appear darker in colour. By itself it is hard to tell, but if you’ve got a couple of old jam jars laying around (or any clear glass container really), put a bit of known-to-be-new fuel in one, and some suspect fuel in the other. If the questionable fuel is darker, you know it’s been sitting quite a bit longer.

The other telltale sign is the smell. It takes a nose that’s been playing with fuel a lot of years to be able to pick it up right away, but even for the newer players, you’ll notice it’s got a sour, or ‘off’ whiff to it. Our dear Head of Content, Isaac, tells me it’s at this point I should mention you shouldn’t go around deliberately sniffing fuel, nor discussing the bouquet of your latest batch of fuel. Aside from the health side-effects, your neighbours will start talking.

How long does fuel take to go bad?

This one is like determining the length of a piece of string. It depends. Most fuel that’s been stockpiled will start to turn bad within a few months, and will be well and truly on it’s way to being shot by the 12-month mark. That said, depending on fuel producer to fuel producer, many add oxidation inhibitors, and some more than others, so some fuel will keep better than others. Unfortunately, this type of information is a fairly closely guarded secret, that we’d never be told by the manufacturers. Rule of thumb here, use any fuel you’ve got stored within about three months of purchasing. This gives a month or two lead time (from when it was brewed by the refinery, put on a truck, and shipped to your local fuel stop), and a couple of months sitting in your garage.

Can you stop fuel going bad, or save some older fuel?

Absolutely you can. There are many fuel ‘stabilisers’ on the market that you can mix with fuel to be able to store it for longer periods of time. These include added oxidation inhibitors, and often an octane booster of some description, among other things. Each product will have its own ‘storage time’ information, so you’ll need to look at how long you can/should store fuel with an additive on a case by case basis. The only caveat to fuel stabilisers, is that you need to add them before you store the fuel for 12-months. They won’t help after the fact.

If you’ve got a 20-litre jerry can of fuel at home that may be starting to fall over, instead of getting rid of it, you can decant half between two jerry cans, and top the rest up with fresh fuel. The higher octane rated fuel you can get here, the better. As aside from starting to become gummed up, the octane rating will be reduced from the original value. A higher octane rated fuel, or even adding an octane booster on top, will see the RON increased back toward where it was pre-storage.

So, should I stockpile fuel at home, at risk of it going bad?

The short answer is probably not. Unless you’re already set up with the storage and fuel goes back up toward $1.40/litre.

See you’ll need somewhere to store the fuel. Fuel drums aren’t cheap, and you’ll need to be able to store the fuel in an airtight drum or container – and it will need to be kept somewhere safe. And then you’ll need to add in some stabiliser if you’re going to keep the fuel, and that’ll cost you around $28 to treat 76 litres. That works out at around $0.37 a litre for the stabiliser. If you’re paying $1.00 a litre for quality 98RON, add to it the cost of the stabiliser you’re up around $1.40 a litre, and the fact you may need to add an octane booster to ensure it runs properly in your vehicle as the octane rating will reduce over time… in the long run it’ll end up costing you more.

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Hailing from the depths of four-wheel driving cosplay goodness, and being the camera-shy, dark-shaded hero we need (maybe not want, but certainly need), Pete has been four-wheel driving his whole life. Offering up how he got it wrong, so you can get it right seems to be his superpower, while also having an innate ability to break things while testing them, ensures the products he tests (and breaks) will hold up to being used by you.