How Long Does It Take for Gas to Go Bad?

Gas is a highly refined product, comprised of distinct chemical composition with highly flammable traits. One significant aspect of gas is volatility, which refers to the ability and condition of gas to vaporize so that it can burn efficiently in your engine. The components of gasoline that are extensively volatile evaporate over time. When this happens, the volatility of the remaining fuel and its ability to combust effectively reduces. The lesser the fuel’s volatility, the lesser its effectiveness while burning in your car’s engine, which in turn, results in poor performance of your car’s engine. In extreme cases, your engine may fail because of the continuous use of poor quality fuel.

Gasoline may go bad with time. When this happens, the gasoline may ruin your vehicle fuel system’s component. Therefore, before you add stored gas into your car, tractor, mower, or any other equipment that uses gas, you should check the expiry date of the fuel as per the manufacturer’s guidelines. However, old gas may not necessarily be bad or contaminated. When stored well, old gas is as functionally good as new gas.

How Long Does Gasoline Last?

Gas expires within 3 to 6 months. The time it takes to expire depends on a multitude of factors such as how the gas is stored and how much heat, oxygen and humidity come in contact with the gas. All of these can lengthen or shorten the amount of time it takes for your gas to go bad. For example, if the gas is exposed to oxygen, then it’ll last a lot less than 6 months. The same goes with heat.

When gas starts to expire, it starts to oxidize and evaporate which means that it loses its combustibility. All this happens within 3 to 6 months. Different types so f gas such as ethanol blends have a shorter shelf life while fuel stabilized gas can last between 1 to 3 years when in optimal conditions. The gas in the tank of your car starts to lose combustibility after one month of being in your car.

Up to Half a Year for Properly Stored Gas

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Even though gas stored over a long period loses its effectiveness because of exposure to oxygen and loss of its volatile components through evaporation, if gasoline is stored properly, it lasts up to six months. According to the fire department’s recommendation, the gas stored in a metal tank or a plastic container, filled to capacity and sealed tightly, lasts up to six months. Usually, the recommended capacity is not more than five gallons. However, if the gas has no impurities and uses fuel stabilizers you can lengthen its lifespan.

Up to Three Months for Ethanol-Blended Gas

The shelf life of ethanol-based fuel is often up to three months due to the rapid of ethanol oxidation. Ethanol will also rapidly absorb humidity or water resulting from condensation within the container, due to its hydrophilic nature. This contaminates the fuel as it adds moisture into the mixture, which eventually separates the fuel into two layers, which are ethanol and gas layers. High amounts of ethanol in a gas significantly reduce its lifespan.

Up to Six Months for Pure Gasoline

Even though it is inevitable for oxidation and evaporation of volatile compounds in petroleum-based gasoline to occur in sealed tanks or containers, the process is often significantly slower in pure gasoline. So, when the gas is well stored, it will last for at least six months. Also, because pure gas is entirely hydrophobic, absorption of humidity or water will not occur as in ethanol-blended gas. Therefore no contamination of gas by moisture or separation of fuel will transpire.

One to Three Years for Fuel-Stabilized Gasoline

Fuel stabilizer (view on Amazon) is an additive put into gasoline before storage to slow down the process of oxidation and evaporation of volatile compounds to prolong the gas’s shelf life. The stabilizers should be used in new and fresh gasoline as it is ineffective in delaying degradation in gases that are already old. Stabilizers cannot also purify contaminated gas. There are various stabilizer brands, depending on the brand you choose to use, the shelf life of your gasoline can go up to one to three good years. It is therefore recommended that you mix it with new gas.

How Can You Differentiate Between Old and New Gas?

Pour a little quantity of the same kind of freshly pumped gas and stored gas into two different glass containers and observe them side by side. Compare the smell and color of the two gases. The old gas should smell kind of sour and have a darker look compared to the fresh one. The gas is probably not contaminated, just old, and lacks efficacy.

Two different layers of ethanol-blended gas and gas will be seen. The gas layer will be set on top of the ethanol layer, which is lighter. This means that there were moisture contamination and separation of the fuel. Considerably discolored gas that looks like rust or perhaps milk chocolate means the gas incorporates sludge or sediment contaminants caused by moisture or oxidation solid by-products.

Can You Use Old Gas?

Old gas is not necessarily harmful. Old gas can be used again if mixed with fresh gasoline. However, the combustibility of the mixed fuel will be lowered, and this may cause sputtering or difficulties when starting the engine. In a gas-powered lawnmower, one-part fresh gas and two parts old gas in the fuel tank will do the trick while in a fresh automobile gas should take three-quarters of the gas cylinder topped up with a quarter of old gas because it needs more horsepower.

What Causes Gas to Go Bad


Gas contains hydrocarbons that react with oxygen to generate new mixtures that alter the fuel’s chemical composition eventually. This results in the deposition of varnish and gum in the fuel system. The impurities and deposits end up clogging filters, gas lines, the tiny orifices found in the carburetor, and the others in the fuel injector (these orifices are even tinier). This will significantly affect the performance of your automobile if not fixed. It is quite costly to remove these deposits.

Water Contamination

Water condensation from heat cycling may occur within your gas cylinder or lines. Fuel containing a high concentration of ethanol alcohol, such as E85, is very vulnerable to water contamination. Ethanol is highly hydrophilic; it absorbs water and moisture from its encircling air. Gas stations with no or light traffic usually have water contamination problems as they have different heat cycling types.

The temperature in the underground fuel storage tanks tends to increase and decrease regularly; this is often resulting in moisture forming and contaminating the fuel. Filling up in stations like that w result in pumping gas along with the water. Fuel does not do well with water; it causes problems when starting the engine and instability when accelerating. It also causes rust in the gas tank and lines.


Gas can be volatile which means that it vaporizes at a rate that’s beneficial for your car engine. Due to this vaporizing characteristic, it does mean that the gas will continue to vaporize regardless of if the engine is using it or not. As the gas continues to vaporize, it’ll become less and less combustible meaning the good effects it has on your engine will decrease.

Change In Chemistry

Over time, the gas in your tank can change in chemistry and this can happen pretty quickly. The rate at which this happens is increased if you’re not using the gas in your tank or you aren’t topping it off with fresh gas. After a month, the chemical changes start to occur in your gas tank from when you filled it up at the station. As time goes in, the chemical changes will start to have more damaging effects.

The Effect Bad Gas Has On Your Vehicle

Now that you’re aware of gas and its chemistry, you may be wondering how it can influence your vehicle. You may be considering starting your car or motorcycle again for the summer after a long time of inactivity. Or maybe you use your vehicle occasionally and it doesn’t require routine fill-ups.

Sadly, using bad expired gas on your gas car or motorcycle can affect the engine in catastrophic ways. When gas fully does bad, not just a few months of deterioration, it gas start to collect varnish deposits and gel up. All the small valves and jets that gas has to go through need to remain clear in order for gas to travel through them. If the gas is gelled up due to deterioration, it’ll be impossible for it to travel through the jets and valves and get to the engine.

One of the worst effects old gas will have on your vehicle is that it’ll clog up the fuel system. Since gel gas is thick and has a lot of deposits, it has a harder time combusting than bad gas so the performance on your vehicle will be a lot less. If you leave this untreated, your vehicle will no longer be able to start or run for very long. This is due to gas clogging up the fuel system and not getting to the engine.

Signs Of Bad Fuel in Gas Tank

If you are uncertain whether or not your fuel has gone bad in your gas tank, there are indications from your vehicle that you can look out for to determine if your fuel is degraded or old.

Acceleration Issues

If you do not immediately accelerate once you step on the gas pedal, then there is reluctance from the engine. This reluctance can be due to degraded fuel in the internal combustion chamber. Your vehicle may take some time to react to the gas pedal before it speeds off. Sometimes it may not speed at all. The more you accelerate, the more obvious this issue will be.

Erratic Speed Changes

Besides accelerating issues, your vehicle will also experience random disruptions to the velocity you are driving at even when you are not stepping on the gas pedal at all. The speed you are driving at will randomly shift with no plausible reason. This is a clear sign that you might have degraded fuel in your gas cylinder.

Damaged Fuel Filter

The function of the fuel filter is to ensure that debris and dirt do not enter into the gas tank and contaminate the fuel. The engine’s smooth performance relies on this; otherwise, there would be a devastating outcome. A ruined fuel filter implies that your fuel has gone bad. Regularly check out the fuel filter to ascertain that it is not faulty.

Problem Starting the Engine

If your fuel has excessive quantities of impurities or water mixed with it, starting your vehicle’s engine will be difficult. However, this symptom is not only unique to this problem since there are several other reasons why you are having problems starting your engine. This sign, coupled with the other signs, indicates bad fuel.

The Engine Stops Running

Imagine driving along the road hurriedly, then suddenly, your engine stops? Well, this happens when you have degraded fuel since the process of internal combustion won’t produce sufficient power to sustain the functions of the engine. This will stop the engine from running as it should.

Little or No Idle

You may notice that your vehicle starts right up, but when you come to a stop it shuts off rather than idle. If it does idle while at a stop sign or light, it will sputter instead of idling smoothly. These are signs of a clogged fuel system due to bad gas.

Loss of Engine Power

This is a common symptom of a failing fuel system due to bad gas, as insufficient amounts of fuel are getting to the fuel injectors. Less fuel means the engine will output less power. If the filter is dirty or clogged, the ECU will reduce the engine output in Limp mode.

Check Engine Light Illuminates

This sign is not particularly unique to bad gas since numerous other problems have the same sign. However, if you have experienced all the other signs of bad gas, then you should probably check the condition of your gas. The simplest way is by dipping in a dipstick in your gas tank, check the color and the smell of the fuel. A darker color than the normal one indicates bad gas, and an unusual sour smell from the gas also indicates bad gas.

You Need to Know This About Your Fuel

if you don’t maintain your fuel system, it can lead to failures such as the one you’re experiencing now. Car parts need to be looked after regularly because they’re constantly working. If you want to prevent problems like this in the future, then you’ll need to make sure that you’re maintaining your car.

If you want to avoid low fuel pressure problems or other issues and save $100s of dollars that you’ll spend at the auto repair shop, you’ll need to service your vehicle often – you can use our mechanic-rated Auto Maintenance and Repair Manual to do this. It’s basically what mechanics use to go through your vehicle to check if there are any problems that need fixing. As soon as they notice the most minor problem, they’ll ask you to fork out some money even though it’s a problem you can fix yourself in minutes – the manual will teach you how to maintain your vehicle every few thousand miles and it’ll teach you how to fix minor problems that mechanics will ask you to pay for; saving you money in the long run.

A lot of our readers have the Auto Maintenance and Repair Manual printed on their garage wall and 92% of them haven’t visited the auto repair shop in the last year because they know what to do to avoid problems. All it takes is giving your vehicle a little attention every few thousand miles and you’ll never spend money at the workshop again.

Identifying Bad Fuel

When the chemical properties of gas change, fuel can’t travel to the engine properly. There are several indications that your gas has gone bad with the most obvious one being the check engine light. If you notice that your car is driving fine, the check engine light may go on because it notices that fuel is being burned improperly which is the bad fuel in your car. If you’ve diagnosed this using an OBD2 scanner (view on Amazon) which helps to diagnose the check engine light, then you’ll need to go to a mechanic to get the problem fixed.

If your car starts to experience operational problems, it’s also a key indication that the fuel has gone bad. This can include starting problems, a rough idling sound, loss or power when accelerating, or a hesitant ignition.

Another key indication of it your gas has gone bad can be determined by its look and smell. Bad gas looks darker and has a dark brown muddy appearance. The odor will also be foul and sour-smelling, not like normal fuel.

If you notice any of these signs, then you need to remove the bad fuel from the tank. This is to prevent your engine from complete damage. If it doesn’t get to this point, the vehicle won’t operate like it should since bad gas can cause damage to the fuel system due to the gel-like gas clogging it up. Bad fuel can also draw in water condensation which can corrode the tank and fuel system. If this isn’t looked at properly, the damage can cost a lot to repair.

How to Stop Gas From Going Bad

If you’ve ever cleaned out bad gas from your vehicle, you’ll know it’s something you never want to do again. If you want to prevent this, there are a few things that you can do to keep the fuel system in check and unclogged with bad gas.

Buy no more than You Intend to Use

Fuel tanks should always be filled up to avoid condensation If water. However, if you don’t intend to use your car for a long period, for instance, putting it in storage for winter, do not leave it half full or top it off. This may cause the vapor recovery system of the tank to get damaged.

Only Buy Fresh Fuel

Usually, fuel stations with the most customers are trusted more since the fuel pumps are frequently used probabilities are high that they have new fuel always.

Ensure that the Gas Cap Fits

The gas cap prevents impurities or contaminants such as dirt, water, or debris from getting into the fuel. Loose-fitting gas cap or completely no gas cap will leave the fuel exposed to contamination. Regularly check your gas cap to make sure that it fits and is in place. If not replace it immediately, this is inexpensive and easy to fix.

Fuel Stabilizer

Fully fill your gas cylinder then mix in the stabilizer. To be certain the mixture incompletely mixed and is circulating through the fuel system, drive your car around for about 10 minutes or more. This increases the lifespan of your gas significantly.

Adding a stabilizer if you plan on leaving your car or motorcycle sitting around for a while is crucial. A fuel stabilizer is a solution that protects gas that’s lying around and not doing anything in the engine.  The stabilizer bonds with the gas it’s mixed with and this stops the gas from vaporizing as quickly. It can increase its shelf life from 3 to 6 months to 1 to 3 years. This is due to the stabilizer slowing down the oxidation reaction.

Drive Your Car

Another preventive step that you can take to stop your fuel from going bad is to drive your car often. Even if it’s not a long journey, driving some short distances a few times each week will help to keep the fuel system in check. Doing this also means that you’ll have to refill your tank every month or fortnight will new fuel which will replace any fuel that’s going bad.

Water In Fuel

If vapor gets into your fuel, it can cause problems. Fuel like diesel includes biodiesel which has a higher water content compared to other fuels like gas. If the water isn’t separated from the gas, it can get into the fuel injectors which will lead to problems. In a normal fuel system, the average pressure used to put the fuel to the engine is around 40,000 PSI. If water finds itself into the fuel injector and it’s moved at extremely high pressure, it may blow the fuel injector’s tip-off which is a very expensive fix.

To reduce the amount of water in the tank, making sure the tank is fuel will reduce the amount of space condensation can take up which means less water can get into the tank. Water in the tank can lead to corrosion of the fuel system which can spell havoc. When the tank is full, it also reduces the amount of oxygen in the tank which will limit the amount of evaporating that the fuel goes through.

Empty The Fuel Tank

If you’re going to leave your fuel tank empty for a while and you don’t want the gas to expire, then it’s best that you employ the tank and fuel system altogether. Although water vapor can still get into the fuel system and gas tank, it happens less when it’s been taken out and stored properly.

Keep In Airtight Container

If you don’t want the fuel to expire, and you don’t plan on driving your vehicle for a long while, you can keep the gas in an airtight container, low oxygen, cool, dry, environment. Doing this will give the gas a longer shelf life due to the good environment it’s in. When the gas is stored in a high heat humid area, it increased the risk of fires and an explosion due to its volatility. Make sure to store low amounts, preferably below 5 gallons as anything more is increase the risk of a fire. When storing the fuel, make sure that you keep a label that contains information on when it was bought and stored so you know which container to take out first.

Diesel Fuel Treatment

Using diesel fuel treatment will separate the water from the fuel. In all diesel engines, a fuel water separator filter is used and the vehicle’s performance is improved by the demulsification. All OEM manufacturers suggest that you demulsify your diesel fuel to make sure that there’s no water in there that can damage your engine.

Use Dual-Phase Biocide

If you want to prevent the development of micros, adding maintenance doses of dual-phase biocide twice a year will prevent this. To prevent oxidation, you should also use a diesel fuel stabilizer. Diesel fuel is different from gas in the sense that it requires a lot of special equipment to work properly.

Go to Popular Stations

While you don’t want to wait in long lines at the gas station, it’s helpful to choose one that is busy. By going to a gas station that has a regular flow of customers, you know that the fuel is constantly new.

Going to popular gas stations to get your gas can also prolong its shelf life. this is because the customers cause the gas to run out more often which means that it’s constantly being replaced with fresh gas. Waiting in the long lines at the gas station is annoying, but it’ll help your gas last longer. If you want to save more time, you can go to the stations during their off-hours which means that you’ll still gain the benefits of fresh gas without having to wait in line.

Storing Gasoline

You may consider storing gas in your garage for uncertain times. If this has been thought, you need to consider how long it’ll take for the gas to go back. Experts don’t think storing gasoline is a smart idea if you don’t plan on using it within 6 months due to how quickly it goes back. Using a fuel stabilizer will help to preserve the gas and make it last longer, but it isn’t a long-term solution. Even with a fuel stabilizer, gas will start to go bad after a certain point.

Making sure that any fuel you want to store is DOT approved in a tightly sealed bottle will give it longer shelf life. Using compact gas can’t that don’t have vents like old gas cans will prevent evaporative emissions which will extend the gas’s shelf life.

How to Dispose of Bad Gas

Bad gas is very volatile and can pollute the environment if disposed of in trash containers on the ground or in sewers, lakes, or drains. Please do not dispose of them carelessly, get hold of your fire department or city waste management to confirm the gasoline disposal site that is approved. Be certain that the container for storage is tightly sealed; put it in a cooler to stop the gasoline from leaking while transporting the container.

The AAA doesn’t recommend stocking fuel for emergencies due to people generally not needing it until it points. Another downside of this is when you realize that you can’t use this old fuel, you can’t just pour it down the drain, you’ll need to dispose of it at a recycling plant.

Bad or contaminated gas should not be used to power vehicles or equipment as it can heighten corrosion or leave varnish deposits or sludge on components of the fuel system severely damaging them. As much as bad gas has poor combustibility, get rid of bad gasoline as soon as you can because the vapors emitted by the gas and the gas itself are still combustible and can cause fire explosion, especially if the gases leak into the surrounding.