Home Fuel System How Long Can Gas Sit In A Car – A Detailed Guide

How Long Can Gas Sit In A Car – A Detailed Guide

by Kelvin Yates

Cars are something that we all use for our transportation. Hence, why worrying about how long can gas sit in a car is a valid concern. Going to the office in the morning, dropping your child at school, most of it is done by our vehicles. But since the pandemic of Covid-19, cars are not used as much as before. We don’t go out that much. Work and education are done at home and most of us are now shopping online.

So there is no real need to bring out the car for a spin. Our cars have been sitting idle in the garage/ parking for months now. Most of them have gas/ gasoline in their fuel tanks. Is it a good thing? We have heard people saying that gas goes bad. But for how long can gas sit in a car? That is what we are going to discuss in this article.

Is It Okay To Let Gas Sit In A Car?

Is it okay to let gas sit in your car’s fuel tank or the system of your car? How long can gas sit in a car? That depends on the type of gas/ fuel and length of idleness.

The shelf life of gasoline is usually higher than the tank life. When gasoline is poured into your car’s fuel tank from its sealed container, it is exposed to the environment. The environment affects the formulation of gasoline in many ways and that causes the gas to go bad.

So, it is not ok at all to let gas sit in a car. Modern gasoline is formed by mixing many substances and chemicals. One of the important chemicals/ ingredients used in gasoline is ethanol alcohol. Ethanol Alcohol is hygroscopic. So it absorbs water vapor from the air.

This not only deforms the gasoline sitting in the tank, but also corrodes the tank and other components.

There is more than one danger of letting gas sit in your car for a long time. Most of the gas you get from filling stations is meant to be used in less than three to five months. They oxidize with the air and corrode your car’s fuel system. That will cost money to repair/ replace. So it is not okay to let gas sit in your car for a long time.

How Long Can Gas Sit In A Car?

How long can gas sit in a car? All the gas/ gasoline that you can get from fuel filling stations in the US is good to sit idle for 3 to 5 months in your car tank.

A fully-sealed container of gas can last for more than a year. It is because the gas is not exposed to the air or the external environment. But the car fuel tank is not sealed. It has ventilation that makes the gas exposed to air. The air is the main reason why gas goes bad sitting in your car.

The air slowly reacts with the gas/ gasoline inside the tank and slowly deforms the gas and makes it go bad. Now depending on the environment and the type of fuel you have in your tank, the gas can go bad in between one to six months. If your car tank has left-over corrosions and there is air in the tank (When not full), the gas will deform quickly.

Gas for cars/ Gasoline has many chemicals and some of them are hygroscopic. This is what causes it to go bad in the first place. We can stop these hygroscopic chemicals in gasoline from reacting by using gas stabilizers. It is a liquid chemical that you can find in the local market.

Let’s summarize how long gas can sit in a car:

  • Gas can sit in your car fuel tank for 3 to 5 months.
  • If the environment is ideal, the gas in your car tank can go bad in less than a month
  • Gas/ Gasoline stabilizers can expand the shelf life of gas in your car tank up to 12 months or more.

Why Does The Gas On My Car Go Bad?

Gasoline does expire and go bad. There is nothing you cannot do to completely prevent gasoline from going bad. It is a natural process. The reason why gasoline expires can be explained by four factors – Oxidation, Evaporation, Temperature, and Water.

Let us explain these four factors and how it makes the oil go bad.

1. Oxidation

What is oxidation? Oxidation is a spontaneous process that changes the structure of molecules by making them lose electrons. It is caused by oxygen.

Oxygen is present in gasoline/ gas and it causes combustion which causes the car engine to run. But this Oxygen is what causes the gasoline to oxidize. Many hydrocarbon elements in gasoline make up most of the gasoline. Oxygen changes the cell molecular structure of these hydrocarbons. Because of the altered structure, the hydrocarbons do not combust with Oxygen as it was supposed to.

How Long Can Gas Sit In A Car

As the gas cannot combust, it becomes useless for running your car.

2. Evaporation

There are many ingredients in gasoline. They all work together to react with oxygen and combust inside the car’s cylindrical heads and make your car engine run. The chemical balance of these ingredients in gasoline makes the perfect combustible. If the balance is ruined, then the combustion will not be good enough.

Unfortunately, another natural process called evaporation is responsible for ruining this chemical balance of gasoline. There are some heavy ingredients as well as some lightweight liquid ingredients in gasoline. The lightweight ingredients can vaporize the air easily. It happens very often in summer when the temperature is hot. When this happens, the chemical balance of gasoline is lost.

Then the gasoline goes bad and cannot create powerful combustions to run the car. If this is the reason for your gas going bad, then your car’s mileage will reduce. Because it will have to use more gasoline to create powerful combustion for running.

3. Temperature

We all know that temperature has some effect on everything. The gasoline in your car tank is no different. Gasoline has a thermal breakdown for both hot and cold temperatures.

When the temperature is too hot, the oil will lose its weight because of the evaporation of light elements.

This reduces the viscosity/ thickness of the oil. This causes less power in combustion. So the car had to increase its oil consumption. This also increases leftover deposits to build up quickly and you will have to take your car for maintenance.

How Long Can Gas Sit in a Car

Now when the temperature is cold, the gasoline inside the tank forms sludges. The oil also becomes too thick sometimes. This causes complications in the fuel system and the oil does not flow properly.

Moreover, the sludges will build up in the fuel pipelines of the engine and completely block the oil from flowing. In these types of situations, you have no choice but to take your car to maintenance. The car may need a full oil change to run properly.

4. Water

Adding water to gasoline will ruin its chemical balance. Then the gasoline can’t combust in the engine cylinders.

It is unusual to hear that someone will mix water with gasoline. But there is one element in gasoline that attracts water. It is called ethanol. We mentioned earlier that ethanol is hygroscopic. That means ethanol attracts water from anywhere.

There is water vapor in the air and ethanol will attract them. The car fuel tank is not sealed. It is vented for accompanying oil flow in the car. So there is enough water vapor in the gas tank. That is enough for the ethanol to consume and your gasoline will be ruined.

Fortunately, the process has a low reaction rate. If your gasoline has 10% ethanol (standard in the USA), then the reaction will take about 3 to 5 months to make your car gas go bad.

But some companies have a high percentage of ethanol in their gasoline. Those create powerful combustions. But the high rate of ethanol also makes it attract more water. So how long can gas sit in a car if they have a high percentage of Ethanol? These kinds of gasoline cannot last more than one month idle in your car gas tank.

So, these four are the main basic factors that cause your gas to go bad. Bad gas is bad for the car.

What Happens To The Car When It Runs On Bad Gas?

Bad gas is bad for cars. We are all aware of this fact. But have we ever thought about how it is bad? What happens to our cars when we make them run on bad gas? What are the dangers?

There are many and making your car run on bad fuel may cost you heavy repair and maintenance. We have discussed the main dangers that can happen to your car if it runs on bad/ expired fuel.

Engine Trouble

Engine trouble will be the major issue for running your car on bad gas. Bad/ expired gas becomes solid and sticky. It creates a sticky jelly-like substance. This substance will build up in the pipelines and engine valves. These are some important engine components. If they are damaged, or cannot operate properly, your engine will fail.

If the oil build-up spreads all over the engine, it will cost you expensive maintenance. Moreover, this can cause a burning smell in the car while driving.

How Long Can Gas Sit in a Car

In the worst-case scenario, your engine may stop working in the middle of the road and leave you stranded.

All of this big engine trouble is caused by only using bad oils. So if you want to take care of your car and treasure it, do not use bad/ expired oil to run it.

Damaged Fuel System

The fuel system, by which the fuel circulates into the engine, is the next big target of expired fuel.

Bad/ expired fuel usually becomes dense and sticky. This makes it very difficult for the fuel to go through the pipelines, fuel pump, and fuel filter.

The filter loses its capacity due to added density and the fuel pump fails to pump the dense liquid. The dense gasoline is then stuck in the fuel line and builds up there. This blocks the fuel line. So even after changing gas, the new gas will not be able to flow because of the build-ups.

The build-ups also cause more damage by rusting the fuel system. Although your car may have corrosion-resistant fuel lines, the build-ups can do heavy damage. The filter and the pump may have to be replaced entirely. Without them, the engine won’t work and the car won’t run.

Low Mileage

Bad fuels do not create powerful combustion like good fuels. So if you’re running your car on bad fuel, it will have to consume more fuel to generate enough power. This increased fuel consumption will reduce the mileage for your car.

Fuel shell station pump filling up Chevrolet Corvette

This reduces the efficiency of your car.

Acceleration And Speed Issues

Bad fuels will cause issues in the engine and fuel intake. This will cause acceleration and speed issues. As the fuel pump is failing to pump the thick gasoline properly, your engine will not work at its best. So even if you press hard on the accelerator, the engine will hesitate to accelerate. That is because the bad gas is causing trouble for fuel intake.

Also, the bad gs will cause fluctuation in the fuel flow. So this may cause your car to rapidly speed down and up. This can cause you many dangers while driving down the road.

So these are some of the main dangers that you will have to encounter while driving on bad fuel. As you can see, it can significantly damage the engine and other components required to run the car.

Modern cars have very sophisticated engines that may put a dent in your wallet for repairs. So if you want to avoid all of that, spend a few dollars for changing the bad engine oil in your car.

How To Identify If My Car Gas Is Bad?

The problem with car gas tanks is that they are not transparent. We cannot take a peek inside of the gas tank to see the gas and judge its condition. All we have is the fuel level indicator in the dashboard.

So are there any reliable ways for judging the gas condition in the fuel tank and identifying bad gas? There are some ways. We have discussed them below.

How Long Can Gas Sit In A Car: Blinking Engine Light

The simplest way of knowing that you have bad gas in your car is by looking at the check engine indication in the dashboard. Is it blinking? If yes, then you may have bad gas in your car.

However, it can be misleading. The check engine light is designed to notify the driver of any sort of issues in the car engine. But the indication cannot tell you what went wrong with the car engine.

For example, it can be a disabled spark plug that is causing the engine to run badly. If you change engine oil there, the problem will not be solved.

So if you see your check engine light blinking, the best thing to do will be to take it to the mechanic and inspect your car properly. But you can guess by remembering the answer to – “how long can gas sit in a car?” If the car was ideal for more than 3 months, then the probability of bad gas is higher.

How Long Can Gas Sit In A Car: Difficulty In Starting The Engine

Bad gas does not generate enough power to run the engine properly. This may create difficulty in starting the engine.

If you are taking your car out after a few months and having trouble starting its engine, then there is a strong possibility that your car may have bad gas in the tank.

Can it be any other engine trouble? If it is, then the check engine light will blink. This can mean many things that can go wrong in the engine. If you recall how long gas can sit in a car, then you may remember that car gasoline goes bad after 3 months of being idle.

Our suggestion here is to siphon the old gas out and put new gas. Then try starting the engine. If you are still having trouble, then you should take it to a mechanic.

How Long Can Gas Sit In A Car: Damaged Fuel System

Bad gas can not only reduce engine performance but also permanently damage the fuel system of your car. The fuel system is one of the most volatile parts of the car. It is also the most important part because the engine cannot run without getting fuel.

If you are noticing a fuel leak under your car, it may indicate that your fuel line is rusted and damaged. You can further inspect the situation by checking the fuel filter and pump. They may be covered with a gummy substance and give off a bad smell. That is a sure indication that your car has bad gas.

How Long Can Gas Sit In A Car: Trouble In-Car Operation

If you are noticing difficulties in acceleration, mileage, and exhaust, then it can be because of bad gas. It is not a 100% guarantee indication.

But if you are having difficulty with your car’s performance, you should take it to a mechanic.

How Long Can Gas Sit In A Car: Visit A Mechanic

In the “How long can gas sit in a car?” section, we have discussed that gas goes bad after 3 months of idle storage in the car gas tank. So if you are taking your car out after three months, the first thing you should do is take it to the mechanic and get it checked.

There you can ask the mechanic to check for bad gas in your car. It will cost some time and money. But this significantly low cost will save you from all the costly troubles caused by running on bad gas.

Besides, visiting the mechanic is the most reliable way of identifying bad gas in your car. So we highly encourage you to do that.

What To Do If Your Car Has Bad Gas?

If you have bad gas in your car, then you must get rid of it. That should be your priority before starting the car engine.

The best method for it is to call a mechanic. But what if there are no mechanics nearby to come into your garage and treat your car? Then you should resort to DIY methods of cleaning the bad gas.

Here are the steps of removing bad gas from the car fuel tank.

Step 1: Remove The Gas Tank

This step is not necessary. But if it is possible to remove the gas tank of your car, then we encourage you to do that. Removing the gas tank will make it very easy for you to clean it.

But removing the tank can be very difficult.

So if you are unable to remove the gas tank, don’t worry about it. Just continue from the next step.

Step 2: Siphon The Old Gas

If you have removed the gas tank, then you can just flip it to get rid of the bad gas. But if you couldn’t remove the tank, then you have to siphon it out.

Step 3: Take Necessary Measures For The Future

After siphoning the bad gas, you should take some necessary measurements for the future. You can either pour dry gasoline to absorb any liquid leftover in the tank. Or you can pour a gas stabilizer to make the gas last long in the tank.

You are free to choose which measurement you will take. You can also try them both together. There will be no harm in using dry gasoline and gas stabilizers together.

Techniques For Storing Gas Longer In Your Car

How long can gas sit in a car? 3 to 5 months. But there are situations when you may have to keep your car parked for longer periods but you have gas in the tank. So are there any ways of expanding the gasoline’s stable life? There is.

You can increase the gasoline’s lifespan with a gas stabilizer, you can make the gas in your car tank sit for almost 12 months. The stabilizer slows down the reaction of gas to the environment and keeps all the chemicals stable so they won’t go bad.

Tips For Preventing Gas From Going Bad

Here are some tips for gas that may help you prevent bad gas.

Buy What You Need

You should only buy the amount of gas that you will need to get by your daily transportation needs. It is not wise to stockpile gas as it goes bad after a few months.

Buy Gas With 10% Ethanol

10% ethanol is the US standard for car gas. Any higher than that will make the gas quickly oxidize and go bad.

Fuel Storage: How Long Can Gas in a Car Stay Good

  • Due to the pandemic, cars are sitting unused for longer periods, leaving gas stagnant for weeks or months.
  • Gasoline has a shelf life of 3-6 months, diesel can last up to a year, and Ethanol can lose its combustibility in just 1-3 months.
  • It’s difficult to track the age of the fuel in your tank, which could be over a month old when it was pumped.
  • Signs of bad fuel include the “check engine” light, operational problems, and the fuel’s appearance and smell.
  • Bad fuel can cause engine damage and blockages in the fuel line, and can draw in water vapor, corroding the tank and fuel system.
  • To keep gas fresh, make time to drive your car a few times a week, top off your tank when you fill it, and use a fuel stabilizer.
  • Storing excess gasoline should be done in an airtight container within a cool, low-humidity, low-oxygen environment.
  • Regular use of fresh gas is the best way to keep fuel from going bad.
  • If bad fuel is detected, it should be removed from the tank immediately to avoid costly engine damage.
  • Maintaining a full tank limits the amount of oxygen in the tank, which can help prevent evaporation and contamination.


So that was our detailed guide on how long can gas sit in a car? We hope that it was very informative for you. Be sure to take care of your car and always check the gas before starting your car engine after long breaks of a few months.

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