Old diesel fuel can sometimes be saved and used, but only if it still looks and smells clean. If it is cloudy, dark, sour-smelling, or has water or sludge in it, do not burn it. Take it to a household hazardous waste facility instead. Never pour diesel on the ground, down a drain, or in the trash.
Diesel does not last forever. Here is how to tell if yours is still good and exactly what to do either way.
Does Diesel Fuel Go Bad?
Yes. Stored diesel typically stays usable for about 6 to 12 months, less in heat or humidity. Over time it oxidizes, can grow algae or microbes if water gets in, and starts to gel or form sludge. Signs it has gone bad include a dark or cloudy color, a sour or varnish-like smell, and gunk or water settled at the bottom.
If It Still Looks Clean: Recondition and Use It
Fuel that is only mildly aged can often be revived.
- Filter it through a clean fuel filter or fine mesh to remove debris.
- Add a diesel fuel stabilizer and, if microbes are a concern, a biocide made for diesel.
- Dilute it by mixing the old fuel a little at a time into a larger amount of fresh diesel in a vehicle or equipment tank.
When in doubt, use it in lower-stakes equipment like a tractor or generator rather than your main vehicle.
If It Has Gone Bad: Dispose of It Safely
Bad diesel is hazardous waste. Handle it the right way:
- Store it in a sealed, labeled fuel container, not an open bucket.
- Take it to your local household hazardous waste facility or a collection event. Many accept old fuel for free.
- Some auto shops and fuel suppliers also take used fuel. Call first.
Never dump diesel on soil, into a storm drain, or in your trash. It is toxic, it pollutes water, and it is a fire hazard.
Frequently Asked Questions
Does diesel fuel expire?
Yes. It generally lasts 6 to 12 months in storage, sooner in heat. It oxidizes, can grow microbes, and forms sludge over time.
Can you still use old diesel?
If it looks and smells clean, you can filter it, add a stabilizer, and mix it into fresh diesel. If it is cloudy, dark, or sour, do not use it.
How do you dispose of old diesel fuel?
Seal it in a labeled container and take it to a household hazardous waste facility or collection event. Some auto shops accept it too. Never pour it out.
How long does diesel last in storage?
About 6 to 12 months untreated. A fuel stabilizer can extend that to a year or more if it is stored cool, dry, and sealed.