Is it bad to leave Gas in Lawn mower over Winter?

A couple of weeks into the winter, I had a few friends over to the house for lunch. While showing a couple of them around my garage, a friend of mine suddenly stopped seeing my lawn mower tucked away properly. He had just realized that he was guilty of leaving his lawn mower outside in winter conditions that could damage it.

Considering my experience with such machines, he immediately asked me is it bad to leave gas in lawn mower over winter? Leaving gas in your lawn mower over the winter can be very bad for your engine and tank. It can degrade and clog up your carburetor, as well as accelerate rusting within the tank, and can cause catastrophic engine failure if the fuel is not prepared.

leaving lawn mower outside in winter

Read on as I explain myself thoroughly, just as I did to my friend. I will discuss lawn mower storage and gas related queries. “I forgot to winterize the lawn mower” is one of the most common statements I hear from fellow enthusiasts. Don’t worry, I have also got the answers about how to take care of your lawn mower in such situations.

Gasoline comprises a mixture of chemicals that combust within the engine to help provide power to the lawn mower. Ethanol is one of the components in this mixture. Thanks to its volatility, ethanol can easily evaporate and also attract water vapor from humid air.

This causes two problems as a result. The first is fuel degradation due to evaporation. As a result, the stale fuel becomes harder than normal, causing your carburetor to get clogged by gunk formed within the petrol.

The second issue has to do with rusting. The increased presence of water vapor in the tank can corrode the aluminum within the tank, causing it to rust. The rust can eventually mix with the gas and enter the engine, causing severe damage. Old gas can create white rust inside the carb of the lawn mower.

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

If your gas has been stored in the tank itself, then it is most likely to have gone bad and thus cannot be used. However, if you store it properly in an airtight container, then the lifespan of the gasoline can be extended upto 6 months. As a result, you may be able to use the gasoline after the winter.

Gasoline over time loses its combustibility. The volatile components tend to evaporate, which increases the temperature at which it ignites. As a result, it will strain the engine and cause it to misfire. 

— Also read: How to Fix a Backfiring Lawn Mower & How to AVOID it?

Storing the gasoline in airtight containers helps reduce the amount of evaporation. However, gas tanks in lawn mowers are not airtight. As a result, it will suffer from degradation due to the evaporation of the volatile compounds. Airtight containers on the other hand will be able to preserve the gas for upto 6 months before it becomes unusable.

How long can you leave gas in a lawn mower?

Gasoline left in your lawn mower can be left for upto a month. Beyond this period, the gas will go bad due to the evaporation of the volatile compounds in the fuel mix. And then it can cause a lot of issues, so we don’t recommend you leaving the lawn mower outside in winter with a filled gas tank.

Gasoline is a mixture of chemicals designed to ignite easily within the engine chamber, allowing it to provide a power output. However, when these chemicals are volatile as well and can evaporate even at lower temperatures.

In a nonairtight enclosure like a fuel tank, this process can take upto a month to happen d gasoline. Thus, you cannot use it beyond that, as it will lead to the engine misfiring and inefficient combustion while in operation.

What to do if I forgot to winterize my lawn mower?

What to do if I forgot to winterize my lawn mower

It is best to move your lawn mower indoors as soon as possible. Also, drain the leftover gas in the tank completely and replace the existing oil. Do not start your lawn mower until all of the above steps have been completed.

Shift your lawn mower to an indoor storage facility like a garage or storage room. Most of these facilities have temperature and humidity control, which will help slow down the effects of corrosion and evaporation.

Next, drain all the existing gas from your tank. This is essential to ensure that degraded gas does not enter the engine chamber, thereby preventing gunk and rusted metal bits from affecting the engine performance.

 — Also read: Is there a Difference between Lawn mower oil and Car oil?

Lastly, drain the engine oil and replace it with fresh oil for your lawn mower. This will not only help to lubricate the moving parts of the engine but also help to get rid of gunk and other debris from within the engine chamber.

It is critical that you do not start the engine before doing all this, as harmful products can enter into the engine chamber. This can cause damage to sensitive internal mechanisms like spark plugs and pistons.

How do you start a lawn mower that has been sitting out all winter?

Replace the gasoline and engine oil. Check the spark plugs for loose connections and wear. Utilize the choke while starting the engine. Lastly, ensure that your carburetor is not being flooded while starting up the engine.

Gas and engine oil are the two components that can get affected adversely by the drop in temperature over the winter. If you have left your lawn mower outside through the winter, then it is highly unlikely that the mower has been winterized. In such cases, replacing them would ensure optimum efficiency and smooth functioning.

Spark plugs could come loose during the winter due to exposure to high winds. In such cases, your engine will misfire. Check the wire connection and push the spark plug connector to solve the problem of a loose connection.

If not done for a while, your spark plug can be fouled. This means that the tip is covered in gunk and dirt, preventing it from effectively igniting the fuel mix in the engine. In such cases, the tip of the spark plug must be cleaned to allow it to function properly.

 — Also read: When to Change Spark Plug on Lawn Mower?

Sometimes, your engine may struggle to start due to a lack of internal heat. Engaging the choke will help increase the heat within the chamber, allowing the engine to remain self-sufficient eventually. Engage the choke for a while and then disconnect it to help your engine start quickly and easily.

Lastly, if you smell burning gas after starting your engine, it means your carburetor has been flooded with too many gases. In such cases, immediately stop the engine and wait for 5-10 minutes to allow the excess gas to drain.

Can I mix old gas with new gas?

Yes, you can mix old gas with new gas. This will help improve the quality of fuel in the tank. But don’t add one liter of old oil to a 200ml of new gas, make sure the fresh gas has more concentration. 

You can read more about how to store gasoline for a long time from this detailed article by CashCarsBuyer. Fresher gas has most of its chemical composition intact, including the volatile compounds. It is a common practice to mix old gas in the tank with fresher gas from a nearby pump. 

The new mixture within your tank will not be as easily combustible as fresh gas, but will still ignite better than the old gas within the tank. As a result, you will be able to utilize the old gas without wasting it and causing damage to your lawn mower.

What do I do with old gas in my lawn mower?

If the old gas is not contaminated, then you can mix it with new gas to make it usable again. If not, drain it from the tank and transfer it to a container. Ensure proper disposal at a government certified landfill.

Gasoline is a hazardous material that cannot be disposed of like regular waste. Most states have strict guidelines regarding the same. One must transfer the gasoline into certified containers meant for gas disposal. After doing this, you can dispose of it only in government-approved waste disposal facilities or landfills that can handle hazardous waste.

  • Is year old gas still good? If your gas does not contain ethanol and has fuel stabilizers added to it, then your gas is mostly okay for use. If not, then it is highly likely that your gas has degraded and cannot be used without causing engine damage.
  • Can old gas cause a lawn mower not to start? Yes. Old gas has reduced combustibility, which increases the temperature at which it ignites. As a result, the engine may not be able to provide sufficient heat to ignite the fuel mix, preventing the engine from starting.
  • How can you tell if gas is bad? Bad gas will be severely discolored and have a very foul smell. If you cannot visually inspect your gas, then rough idling, stalling while operating the machine and slow engine start-up are other common indicators of gasoline degradation.

3 thoughts on “Is it bad to leave Gas in Lawn mower over Winter?”

  1. Thank you for that wise critique. Me & my neighbour were preparing to do some research about that. Im very glad to see this kind of info which I was searching for a lengthy time.


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