The gasoline in your car began its life (for want of a better term) around 360 million years ago. That’s long before even the first
How long does gasoline take to expire?
It’s true: whilst post-apocalyptic visions of the future like
“Gas does have a shelf life,” confirmed Matt Crisara in a recent article for
With proper storage, that can be extended some: “you can expect anywhere from three to six months with fuel that’s been stored in jerry cans – in proper conditions,” Crisara explained, while “fuel stabilizers can boost the shelf life from anywhere between one to three years in optimal conditions.”
Why does gasoline go bad?
To understand the different ways that your fuel can go bad, we first need to take a look at what
The stuff you pump into your car’s fuel tank is a very different substance from the crude oil that was pumped out of the Earth a few hundred million years after those algae blooms originally died. Sure, at its most basic description, it’s the same: it’s a mixture of hydrocarbons of differing weights, which can be combusted to provide
However, in between that and the gas station, it goes through quite a few important changes. The heavier hydrocarbons are taken out, leaving the fuel as a mixture of paraffins (alkanes), olefins (alkenes), and cycloalkanes (naphthenes); impurities such as
It’s some of these additions which can cause one kind of problem with leftover gas. Ethanol, for starters: it’s put into the mix thanks to its
“If there’s ethanol in your gasoline, it could start sucking in water vapor from the air and putting it into your gasoline,” chemical engineer Richard Stanley told
Then there are the olefins. As hydrocarbons with a double bond between two carbon atoms, these molecules are particularly susceptible to a process called oxidation – they start to react with the oxygen in the air, creating a nasty gum-like solid that can jam up your car’s engine.
“Once [the bad gasoline] gets into the pipeline, that gum may separate out […] and maybe [it will] not block the gas line fully, but maybe [it will] start to block it,” James Speight, an independent fuel and environmental consultant and author of over 100 books and papers on oil refinement and processing, told Live Science.
“You can almost say that gumming of the gas lines is like
That’s not the only way gasoline goes bad, though. Because the fuel is made up of only the lightest hydrocarbons out of crude oil – generally consisting entirely of those chains with 12 or fewer carbon atoms – leaving it too long can actually result in some of those molecules evaporating away. This can be particularly problematic if you’re trying to start your car in the summer using gas that’s been in the tank since winter, Speight advised: petroleum companies
“If you leave gasoline by itself, over time […] it just doesn’t perform the way you think it’s going to perform,” Stanley told Live Science.
Gasoline is “like wine,” he said. “Once you take it out of the bottle, it starts going bad.”
What to do if your gasoline expires
So you’ve decided to go for a drive, only to be faced with a tank full of muddy orange gunk that smells like – in Crisara’s words – “an old gym sock that’s been soaked in milk and left to rot for years.” What do you do?
According to UK automotive services company The RAC, it depends on how full your tank is. “If your tank is full of old fuel (especially old
If you’re running on a bit less than that, you might have a cheaper option. “If you suspect your petrol [aka gasoline] or diesel is stale the best advice is to try topping up with fresh fuel from a filling station,” they write.
Of course, the better tactic is to store your gas in such a way as to maximize its shelf life. “The main enemies for fuel storage are oxygen, water, and heat,” William Northrop, a professor of mechanical engineering at the University of Minnesota, told Popular Mechanics – and so, to increase your fuel’s longevity, you’re going to want to reduce the impact of those effects in particular.
To that end, it’s a good idea to store gas in a fairly full container, Northrop advised: “You’ll evaporate some of the volatile components,” he explained, “but once the concentration of those volatile components gets high enough in the vapor, they no longer want to evaporate because they establish an equilibrium between their vapor phase and their concentration of liquid.”
Even more important than a full container is its surrounding environment. Keep any gas you’re storing somewhere with a constant temperature and low humidity, Northrop advised – and remember: by its very nature, gasoline is really not something you want to treat carelessly.
“Remember, gasoline is very, very volatile,” Speight told Live Science. “It’s not worth trying to store large amounts. It can just result in trouble.”
“Anything that makes the gasoline a little more volatile than it normally is affects the gasoline,” he added – joking that “on a hot day… [that can include] looking at the stuff the wrong way.”
An earlier version of this article was published in March 2023.