Tips from Used Car Advisor

Car Advisor Tamotsu Todoroki

Hi, this is Tamotsu Todoroki. I am a car advisor of
I write an online column every week to take care of your vehicle. My column is all about something useful and practical for your vehicle. Please have a look once to keep your car in good condition.


Will Gas Go Bad (Be Rotten)? - Vol.431

Does gasoline stay good forever? Or will gas go bad if you store it for too long?

Having a full tank of gas in your car may be a good idea. But if you don't drive that often, you may be doing more harm than good. And your engine may suffer for it.

Keep reading to find out how long you can keep gasoline. And signs to look for that your gas is bad. Being prepared will only get you so far if your gas turns before you can use it.

What Is Gasoline?
The gasoline you put in your car differs from the crude oil taken from the ground. The refining process removes impurities and adds additives that can improve your engine's performance. But this carefully balanced product can degrade over time.

Why? Gasoline is mainly a mixture of hydrocarbons (molecules of carbon and hydrogen atoms), usually in the range of 4-12 carbon atoms per molecule. Over time, some of the lighter hydrocarbons (less carbon atoms) evaporate. Other hydrocarbons may form solids, called gum, as a reaction with oxygen in the air.

How Long Does It Last?
So how long can you keep that tank of gas? The answer is approximately 30 days. There are other factors that may contribute to how quickly the gas goes bad. But generally, gasoline starts to show signs of deterioration after 30 days of its life.

Some factors that may contribute to gas going bad include:

- Temperature

- Humidity

- Ethanol content

Furthermore, unless you plan on storing your car for a period of time, you may not run into this problem. Gas stations and vehicles cycle through the gas so quickly that it rarely has time to go bad. But if you have small equipment like a lawnmower, you may see this problem more frequently.

Symptoms of Bad Gas
There are a few ways to tell if your gasoline is stale. If the stale gas is already in your fuel tank, you may experience poor combustibility. Check out the signs that your gas is not as volatile and burning like it needs to:

- Engine light is on

- Knocking or pinging sound from the engine

- Car won't start at all

- Car difficult to start

- Car engine runs "rough"

Bad or stale gas is also noticeably darker than fresh gas. So if you can visually inspect it, that is also a good indicator that your gasoline has gone bad.

What You Can Do
If you know you will be storing your car unused for a few months, you can try using a fuel system stabilizer. You can buy a stabilizer from any car parts store. Simply pour it into the gas tank before storing your vehicle.

This isn't a miracle cure, though. Stabilizers work for 12 to 15 months by slowing down the oxidation process. However, if you plan to store your car for longer than that, you may want to drain the fuel completely. And refuel with fresh gas before you decide to start using it again.

Final Thought
Under normal driving conditions, you probably don't have to worry about your gas going bad. Because you use it up so often, the constant cycling of fresh fuel doesn't have a chance to harm your engine. However, if you decide to store your vehicle, you may encounter problems the next time you try to start your car.

Gas starts to deteriorate after approximately 30 days. So, if you will not be using your vehicle for a month or more, you may want to consider using a stabilizer. Stabilizers can help save your engine by keeping your gasoline fresh for 12 months or more.

Lastly, if you plan on storing your vehicle for longer than a year, even the best stabilizers may not work. In this case, you may want to consider draining your fuel tank completely.