Gasoline typically stays good in your car's tank for about 1 to 3 months under normal conditions. However, this timeframe isn't set in stone; it can be shorter or longer depending on factors like the fuel's formulation, climate, and how the car is stored. The primary reason gas degrades is a process called oxidation, where fuel components react with oxygen, leading to the formation of gummy residues and varnish that can clog your fuel system. Ethanol-blended fuel (most gasoline sold in the U.S. is E10, containing 10% ethanol) poses an additional challenge because it is hygroscopic, meaning it absorbs moisture from the air, which can lead to phase separation and corrosion.
For optimal engine performance and to avoid issues like hard starting or rough idling, it's best not to let gas sit for extended periods. If you know your car will be parked for more than a month, taking preventive steps is wise.
| Factor | Impact on Fuel Stability | Recommended Action |
|---|
| Fuel Type | Non-ethanol (ethanol-free) gasoline is more stable and can last 6+ months. | Use ethanol-free fuel for seasonal equipment or stored vehicles. |
| Storage Temperature | Heat accelerates oxidation; cold, stable temperatures slow it. | Store the vehicle in a cool, dry place like a garage. |
| Fuel Tank Condition | A half-full tank has more air space, allowing more moisture condensation. | Before storage, fill the tank completely to minimize air exposure. |
| Additives | A quality fuel stabilizer can extend fuel life to 1-2 years. | Add stabilizer to fresh gas before storage and run the engine to circulate it. |
| Modern vs. Classic Car | Modern sealed fuel systems are better at preventing vapor loss and contamination. | Classic cars require more diligent fuel management. |
If you're dealing with gas that's been sitting for over six months, it's generally safer to have a professional drain the tank rather than risk damaging your engine's fuel injectors or fuel pump.
