does gasoline go bad in a car

[AdrielDella]

Yes, gasoline does go bad. Modern gasoline begins to degrade and lose combustibility after just 30 days due to a process called oxidation. This is especially true for gasoline blends containing ethanol, like the E10 (10% ethanol) commonly sold in the U.S. The primary risks of using old gas are engine knocking, difficulty starting, and potential damage to your fuel system.

The main culprit is oxidation, where gasoline components react with oxygen, forming gums and varnishes that can clog fuel injectors and carburetors. For ethanol-blended fuel, phase separation is a critical issue. Ethanol absorbs moisture from the air. Over time, this can cause the ethanol and water to separate from the gasoline, sinking to the bottom of your tank. This water-ethanol mixture can cause corrosion and is highly damaging to the engine.

How long gas lasts depends on several factors:

Factor	Impact on Fuel Lifespan	Key Consideration
Fuel Type	Ethanol-free gas can last 3-6 months. E10 gas lasts 1-3 months.	Ethanol-free gas is more stable but often more expensive and less common.
Storage Conditions	Gas in a sealed, approved container lasts longer than in a car's tank.	Heat, humidity, and temperature fluctuations accelerate degradation.
Fuel Stabilizer	Treated gas can remain usable for 1-2 years.	A stabilizer like Sta-Bil is essential for seasonal equipment or stored vehicles.
Age of Gas	Fresh gas from high-turnover stations is always best.	Avoid filling up at stations that may have old fuel in their underground tanks.

If your car has been sitting for over six months, it's wise to be cautious. For a car that won't start, you may need to drain the old gas. If it runs roughly, adding a fuel system cleaner and diluting the old gas with a full tank of fresh, high-octane gasoline can often help clear out minor deposits.

[StEmmett]

Absolutely, it can. Think of gas like milk—it has a shelf life. The stuff with ethanol in it, which is most gas today, starts to go bad in about a month. It absorbs water from the air, and that gunk can clog up your engine. If your lawn mower won't start after winter, bad gas is usually the reason. For a car that's been parked for a few months, your best bet is to top off the tank with fresh gas before you try to start it. It dilutes the old stuff and gives you a fighting chance.

[DeBrady]

From a mechanical standpoint, stale gasoline is a real problem. The volatile compounds that allow for easy ignition evaporate first. What's left is a less combustible fluid that can lead to incomplete combustion, causing hard starting and engine knocking. Furthermore, the gums and varnishes that form can adhere to critical components like fuel injectors, reducing their efficiency and potentially leading to expensive repairs. The fuel pump, which relies on gasoline for lubrication and cooling, can also be damaged by degraded fuel. It's a silent killer for engines that sit unused.

[EllaAnn]

If you're storing a classic car or a motorcycle for the winter, this is your top priority. Don't just park it with a half-empty tank. Moisture condenses in the empty space, accelerating phase separation. Either drain the fuel system completely—which is a lot of work—or, much easier, fill the tank to the top with fresh gas and add a fuel stabilizer. Run the engine for a few minutes to get the treated gas into the entire fuel system. This simple step will protect your investment and save you a huge headache when you're ready to drive again in the spring.

[Kiara]

The short answer is yes, but the "how" and "why" matter most. Modern gasoline is a complex blend designed for efficiency, not longevity. Environmental factors are key: heat increases the rate of chemical breakdown, and humidity introduces water that ethanol blends readily absorb. This is less of an issue for a daily driver that constantly cycles through fuel. The real risk is for vehicles that sit—project cars, seasonal convertibles, or a spare car. Proactive maintenance, specifically using a fuel stabilizer for any vehicle you know will be parked for more than 30 days, is the simplest and most effective solution.