Does Petrol and diesel expire?
Petrol loses its lighter, more volatile fractions to evaporation, which is what makes an engine hard to start on old fuel. Ethanol-blended petrol has a second problem: ethanol is hygroscopic and pulls water out of the air, and past a certain point the water and ethanol separate out as a layer at the bottom of the tank that an engine cannot run on. This is why small engines — mowers, generators, outboards, motorcycles left over winter — suffer far more than cars, which cycle their fuel constantly. Diesel keeps longer but grows a microbial sludge at the fuel–water interface if it sits.
How to store it
- Fill the tank before storing something over winter — a full tank has less air, so less condensation.
- Fuel stabiliser genuinely works, and is far cheaper than a carburettor rebuild.
How to tell it has gone
- A varnish-like or sour smell instead of the sharp normal one.
- Darkened colour, or a visible separated layer in a clear container.
"Use by" and "best before" are legally different. Use-by is a safety date and should be respected; best-before is about quality, and food is usually fine well past it. Where the two diverge matters, the page above says which applies.
Common questions
- Does Petrol and diesel expire?
- Petrol goes stale within months, and ethanol blends go faster because they absorb water.
- How long does Petrol and diesel last?
- Petrol: 3-6 months. E10: closer to 3. Diesel: 6-12 months. With stabiliser: 1-2 years
Related pages
- Does Eggs expire? Eggs stay usable for weeks past the date on the box, and the float test tells you about age rather than safety.
- Does Medicines expire? Most solid medicines keep much of their potency for years past the date — but a handful genuinely must not be used late.
- Does Batteries expire? They self-discharge on the shelf, at very different rates by chemistry — and alkalines leak when flat.
- Does Wine expire? The great majority of wine is meant to be drunk within a year or two. Very little of it improves.
- Does Chocolate expire? It keeps far longer than the date. The white bloom on old chocolate is fat or sugar, not mould.
- Does Household bleach expire? It loses strength within months and eventually becomes salt water. This surprises most people.
- Does Paint expire? Unopened water-based paint keeps a few years; opened tins depend entirely on how well they were sealed.
- Does Flour expire? White flour keeps 6-12 months; wholemeal goes rancid in 3-6 because the wheat germ oil oxidises.
- Does Honey expire? Does not expire
- Does Milk expire? Has a real expiry date
- Does Sunscreen expire? Unsafe or ineffective after the date
- Does Salt expire? Does not expire
- Does Frozen food expire? Indefinite if stored properly
- Does Canned food expire? Indefinite if stored properly
Sources
- US Environmental Protection Agency — EPA (Public domain (US Government))