Don't trust last year's fuel just because it smells okay

The fuel is more likely to be bad than the stabilizer, and it usually announces itself with a sour smell and a darker look.

Fuel stabilizer itself rarely goes bad in a dramatic way. A sealed bottle lasts years, and an opened one usually loses strength after a year or two — maybe thicker or with some sediment if it’s really old. But even fresh stabilizer won’t save fuel that has already started to break down.

What you need to check is the fuel. Stored gasoline (especially ethanol blend) absorbs moisture and oxidizes over time. Bad fuel smells like varnish or paint thinner instead of fresh gas. It also looks darker, cloudy, or has visible junk floating in it. If you see that, don’t put it in an engine. One batch of gummy fuel can clog a carburetor or injector in minutes.

If last year’s fuel still smells like gasoline and looks clean and bright, it’s probably usable — especially if it was stored in a sealed container with stabilizer. But don’t just pour it into something expensive. Filter it through a clean funnel, add a fresh dose of stabilizer, and test it in a small engine like a lawnmower before you risk anything you actually care about.

A $5 container of fresh gas beats a $200 carburetor rebuild.