It’s that time of year again. The weather is starting to get colder, the leaves are changing colour, and the pumpkin spice lattes are back in full force. For many people, this also means it’s time to start winterizing their homes.

But what about your lawn mower? Just because you’re not using it doesn’t mean it can just sit all winter long. In fact, there are a few things you need to do to make sure your lawn mower is ready for spring. So, if you left gas in mower over winter, is that a mistake? Keep reading to find out!

Left Gas in Lawn Mower Over Winter

Left Gas in Mower Over Winter – Is it a Mistake?

On any occasion and on any model of a lawnmower, it is a mistake to leave petrol in the fuel tank of this machine. This is not only bad for the gasoline in the fuel tank itself, but it is also bad for the life and efficiency of the fuel tank and the engine itself. It is also a bad decision for the life and efficiency of the fuel tank and the engine itself.

There are some typical problems and one of them is the deterioration of the carburetor. This part, which is included in any lawn mower, can clog and even degrade. So a deteriorated and clogged carburetor is always a bad sign as it decreases power. Even many lawnmowers can die with a carburetor that is too deteriorated.

The fuel tank can also present some problems when you leave gas in all winter. One of the most obvious problems that can be encountered is the much more accelerated oxidation of the fuel tank. This significantly decreases the life of the fuel stabilizers and is just one of the many problems you will encounter.

On the other hand, it is also possible to find some very serious and even catastrophic failures in different parts of the engine. Keep in mind that gasoline even has different chemical components. Gasoline mixes with air that enters through the air filter to produce the combination that will be converted into power inside the combustion chamber of the engine.

One of the components that can evaporate is ethanol. At the same time, this attracts a dangerous amount of water vapor found in moist air. This characteristic of ethanol has 2 main disadvantages. Firstly, you will have a degraded fuel that cannot be used in your lawnmower.

At the same time, this causes the fuel to solidify to some extent, making it more rancid. So, this clogs the carburetor much more easily, all of which is combined with the dirt accumulated inside. If this is too much, we must still mention the problem related to rust.

You may notice that the rust is greatly accelerated by signs of corrosion on the aluminum that is usually present inside the fuel tank. As mentioned, this is usually caused by the evaporation of ethanol attracting water vapor. When rust enters the engine after mixing with gasoline, the damage is much more severe.

Also Read: Do Zero-Turn Mowers Have Brakes?

How Long Can I Leave Gas in My Lawn Mower?

A lawn mower should be used frequently so that the petrol in the fuel tank can be used and renewed constantly. If you do not need to use your lawnmower for a while, you should take into consideration that the petrol can degrade after a few weeks. To be exact, it only takes 30 days for the gasoline to start to degrade.

This amount of time can be extended when you implement the right factors for it. Properly treated gasoline can remain in good condition for up to a year. This requires a fuel stabilizer that prevents degradation of the gasoline, such as ethanol evaporation.

To do this, it is necessary to consider some basic aspects of the storage fuel stabilizer. Each fuel stabilizer has a specialized storage grade. So, you will need to consider this, as well as the type of gasoline you use to run your lawnmower.

Some storage fuel stabilizers are so efficient that they can provide efficient fuel lines for up to 2 years. Before filling the gas tank for the last time this product should be incorporated into it. After filling the fuel tank, you should use your lawnmower for a few minutes. In this way, the solution will be able to cover the whole system by flowing completely.

What Happens When You Leave Gas in a Lawn Mower?

You should be aware that gasoline alone is not designed to be stored for long periods in any fuel tank. This means that many problems start to occur when you leave gas in your lawn mower for too long. Even the same situation also causes problems in any vehicle.

It takes as little as 30 days for gasoline to degrade and cause problems. Gasoline that has degraded is usually more solid than normal. This is because the ethanol has evaporated as well as other chemical components. So, the thicker gasoline left in your lawn mower can clog different parts of the engine.

One of the key parts that can clog and deteriorate is the carburetor. Even the thickest and most solid gasoline can combine with the conventional dirt found in any engine. No engine oil is equipped to deal with so much dirt inside the engine. Other problems such as accelerated fuel tank oxidation also occur.

Fuel tank oxidation occurs on the aluminum located on the inside of the fuel tank. When this happens, the likelihood of fuel tank leaks is accelerated. This not only decreases the fuel economy of the mower but can also be very dangerous. Finally, the entire engine can have a variety of minor or major failures.

Left Gas in Lawn Mower Over Winter

Does Gas Go Bad in the Cold?

There are some considerations to keep in mind when your lawn mower’s gas tank still has gas in it and the weather is somewhat cold. Gasoline will not freeze and become solid in the fuel lines or in the gas tank itself in temperatures that do not reach -40 °F.

This does not mean that there is no problem with temperature extremes near this limit. One of the drawbacks that can occur is the crystallization of gasoline in extreme temperatures. This is generally not a problem for the engine interior as the petrol crystals are retained by the fuel filter.

Beyond that, it should be noted that the fuel filter will have to deal with a larger amount of objects to be filtered out. This means that the fuel filter can become clogged much more quickly than normal. To prevent crystallization or freezing of petrol in extreme temperatures, anti-freeze additives are available.

One of the most efficient options is isopropyl petrol antifreeze. Some people also prefer to use normal isopropyl alcohol. The most suitable formula is usually to add 12 oz of liquid per 10 gallons of gasoline. In any case, it takes too low an extreme temperature for gasoline crystallization or freezing to be a real problem.

How Do You Start a Lawnmower After Sitting All Winter?

If you want to avoid all problems when starting your lawnmower after sitting all winter, we recommend the following steps.

  • Check the condition of the battery: You can use a battery charger to fully charge the battery and make sure that you do not have a dead battery. It is also advisable to remove any corrosion by using life water. This will keep the battery terminals nice and clean.
  • New petrol: It is best to add new petrol to the petrol tank of your lawnmower. As a second option, you can use a petrol stabilizer if the fuel tank of your lawnmower still has some old petrol in it. If it is only old gasoline, you must remove all the gasoline to add gasoline.
  • Clean the carburetor: Some lawnmowers are fitted with a drain screw so that the carburetor can be drained. This will allow all the old fuel that has been left out of the fuel tank and into the mower system to be drained. Using a carburetor cleaner will allow all the dirt to be removed more efficiently.
  • Cleaning: Thoroughly cleaning a lawn mower can also be very appropriate as part of general lawn mower maintenance. Remember not to wash your lawn mower in the same place where you have drained the petrol.
  • Check the engine oil: Finally, you need to check the level of engine oil in your lawn mower. If the oil has reached its full life, you will need to add new engine oil. Also, read if you want to know if lawn mowers are cheaper in winter?

Can I Mix Old Gas With New Gas?

If not too much time has passed, you can mix old petrol with new petrol. Old petrol should be only 30 days old so that the level of inefficiency is not too high. It is also recommended to mix equal parts of old petrol with new petrol. All this can be efficient only in a lawn mower or other household tools.

How to Drain Gas from a Lawn Mower?

To drain gas from the gas tank of your lawn mower, you will need to have a syringe or pipette, although it is also possible to use a siphon. This is used in conjunction with a hose and a petrol can.

Gasoline between the fuel line and the carburetor can be removed using the drain screw that many lawnmowers come with. This screw is designed to use gravity to drain the fuel from this machine.


Leaving gasoline without any additive for more than 30 days in your lawn mower is a mistake. Gasoline begins to deteriorate after 30 days, becoming more solid and inefficient. This can clog the carburetor and other parts of the mower.

You can use a gasoline stabilizer to prevent gasoline degradation. You can also drain the gasoline from your mower and use new gasoline after the winter has passed.

Related Guide:

What happens if you leave gas in lawnmower over winter?

Stale gas can cause starting and running problems in the lawnmower due to fuel degradation and potential carburetor clogs.

What do I do if I left gas in my lawn mower?

Drain the old gas, clean the carburetor if needed, replace the fuel filter (if applicable), and refill with fresh fuel.

How long can you leave gas in a lawn mower?

Gasoline can typically be left in a lawnmower for up to 30 days without major issues if a fuel stabilizer is used. Without a fuel stabilizer, gasoline can start to degrade within as little as 30 days, leading to potential starting and running problems. It is generally recommended to use fresh gasoline whenever possible to maintain optimal performance.

Will bad gas ruin a lawn mower?

Bad gas can potentially ruin a lawnmower if it is left in the fuel system for an extended period. Stale or degraded gas can cause starting and running problems, clog the carburetor, and lead to engine damage.

Can I use gas that’s been sitting all winter?

Using gas that has been sitting all winter is not ideal. It may have degraded and can cause starting and running problems in your equipment. It’s best to use fresh gasoline for optimal performance.

Victoria Peterson

I am a passionate gardener who wants to help you create and maintain your dream yard. I know that it can be daunting to take on a project like this, but I am here to help. I have been gardening for years and have learned a lot along the way. I want to share my knowledge with you and help you create the perfect yard for your home.

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