Lawn Mower Storage: Why Draining The Fuel Tank Is A Mistake. Gas in oil lawn mower

Why is My Lawn Mower Spark Plug Covered in Oil?

Spark plugs in lawn mowers can occasionally get wet with oil or other fluids, and if you have never dealt with this before, it can be unnerving. This article will outline potential underlying causes of this to help you get your mower up and running again. There are a few potential reasons for a wet spark plug in your lawn mower, but it’s most likely because the plug has overheated due to ethanol in the gas, and the combustion chamber is flooding with oil, or there is water flooding the engine or the fuel and oil tanks. There are a few other potential reasons for spark plug flooding, and it may require servicing to thoroughly clean it. There are a few remedies that you can do yourself, as well as important precautions to take to prevent this from happening again in the future.

What to do instead: Avoid risks with gas stabilizer.

Manufacturers sometimes recommend draining the tank to winterize a lawn mower because the worst thing you can do is leave old fuel in an engine during long periods of storage.

You may have followed this advice in the past without noticeable issues, but that doesn’t mean you’re in the clear. If draining the tank becomes a yearly habit, there’s a good chance you’re shortening the lifespan of your lawn mower and other tools.

There’s a much easier way to properly store your lawn equipment. To avoid damage, simply use a quality fuel stabilizer and fresh fuel before putting equipment away for the season.

Here’s how to winterize a lawn mower correctly

Step 1: Buy and stabilize fresh fuel for maximum protection. Adding fuel stabilizer to old fuel will stop it from degrading further, but the fuel may already have broken down.

Step 2: Fill your tank 95% full with fresh, stabilized fuel. Leaving a little room prevents the fuel from expanding and spilling in warmer weather, and reduces the risk of water vapor that can condense and contaminate fuel.

Step 3: Run the engine for a couple of minutes. This gets the stabilized fuel into the carburetor and fuel lines.

While you should still consult with your manufacturer for product-specific equipment and engine maintenance tips, these simple steps apply to all engines, big and small. A few minutes on each piece of yard equipment can save hours when the grass starts growing and the season kicks off in spring.

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step one is incorrect. an ethanol treatment should be used all of the time. oxygenated fuel @ 10% (e10) adds 3 1/2% oxygen to the fuel and oxygen contains water which can cause “white rust” (calcium and lime) it also enleans the fuel to a mixture from 14.7 to 1 to 15.2 to 1. which can increase the engines running temperature.

We recommend treating the fuel as soon as it is dispensed from the pump This will ensure that the fuel will be kept as fresh as possible and also help keep the fuel system clean. There is no need to add any more STA-BIL Brand unless more fuel is added. In such case, simply add enough product to cover the additional fuel. If the concern is countering the negative effects of ethanol in the fuel system, we highly recommend treating with STA-BIL 360 Performance which will prevent such issues such as corrosion, rust and condensation issues. It will also stabilize fuel for at least 12 months. Please contact us at if you have any questions about this. Thank you.

On step 4 when said to run with fuel stabilizer for couple minites, then do we still leaved fuel stabilizer in tank thru winter?

Hi Larry, after adding fuel stabilizer to a full tank and letting the engine run for a few minutes, then you are done. That’s all you need to do! Please contact us at if you have any questions.

I have been doing the same thing with all my gas power equipment since 1976. [ snowblower, chain saw. gas trimmer. gas power washer, gas power generator. my John Deere lawn tractors right up to my new 2017 X – 570 JD. Just add a bottle of dry gas [ STA – BIL ] Starts right up come spring time. I run that same gas for my 1st lawn cutting then just had fresh gas to the tractor. Never had one single problem.

What if it is already January. and quite cool. (2 degress C at night), ….and I CANNOT start my mower and weed eater easily. Should I just pull the cord to distribute gas and stabiizer?

This will not get the gas into the carb. The carb bowl can be remove and let the fuel run through and then replace. Please contact us at if you have any questions about this. Thank you.

I am new at this and just learned this information. My mower has some gas left in it, and today is the first warm day we’ve had, so I went and bought some stabilizer. Can I put it directly in my tank with the gas it already has left in it and run the mower before storing it for the rest of the winter? I live far from town and don’t think I am able to go get fresh fuel. Thanks!

Yes. It goes directly into the mower’s gas tank. Although it is best to keep the lawnmower’s tank as full as possible prior to storage, treating the remainder fuel with STA-BIL and running the engine for about 2 minutes will help in keeping the system from varnishing (gunk).

I have tried all ways to store my snow blower for the summer and have still replaced the carberator several times. I now have found the answer. I use Tru Fuel available at Home Depot And Lowes. It is gasoline with NO ethanol. I still use stabil and still drain the tank and carb before storage. Been several years now with not one problem. Yea, it’s 20 bucks a gallon but how much do you use a season, maybe two gallons. Less that a carberator

You are correct. It is definitely true that non-ethanol fuel is more reliable than ethanol-blended fuel as it is not as susceptible to condensation, corrosion and rust issues and treating with STA-BIL still must be done to keep it as fresh as possible. However, if obtaining non-ethanol fuel is a challenge (cannot find it or unaffordable), we recommend trying STA-BIL 360 Performance as it tackles those problems while in use and storage.

Sounds like a good idea. I used 360 stabil and pure gas during the season. For me, the gas went bad and made the mower difficult to crank and keep running after about 6 weeks of nonuse. I’ll go back to running it empty at the end of the season.

We are disappointed to hear that our product did not live up to your expectations. There are several reasons that may affect results in storing fuel –from age and quality of the fuel, to the products shelf life (2 years after opening), to storage conditions. So far, in 60 years we have had very good feedback from consumers and STA-BIL is even recommended by many OEMs such as MTD and Generac as well as featuring a Full Satisfaction Guarantee. Having said that, dry storage is also a good option as long as it is done properly as leaving any residue in the fuel system may lead to varnishing, sediment accumulation, corrosion and rust.

Hi Wayne, all STA-BIL products have a shelf life of two years from the time of opening. Unopened it’s 8-10 years. Please contact us at if you’d like help checking the manufacturing date of your bottle.

I’ve been using the red stable for all my small engines (2/4cycle) for at least 30 years with great results. I use sta-bil year around and only buy premium with no ethanol. 2016 I bought a boat with a Yamaha four stroke motor which l use the 360 marine sta-bil. Can I use the 360 marine for all of my equipment or do l need to keep a bottle of the red stable for my lawn equipment?

Hi Dan, you can use STA-BIL 360 Marine for all of your equipment. However, it is more concentrated so be sure to pay close attention to the treatment rate. Please contact us at if you have any questions about this. Thank you.

Lawnmower Won’t Start? Do this.

Bad gas or a dirty carburetor are the most common reasons for a lawnmower that starts hard or runs rough.

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lawn, mower, storage, draining, fuel, tank

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A lawnmower that won’t start, especially when taken from storage, is almost always due to one problem: bad gas.

Storing a lawnmower in the fall without adding gasoline stabilizer to the fuel tank can cause the fuel to break down and plug the fuel passages. If fixing that problem doesn’t help, there are a few others that can help fix a lawnmower that won’t start, as we explain here.

How to Fix a Lawnmower That Won’t Start

Replace the Bad Gas

Over time (like the six months your lawnmower sat in your garage over the winter), the lighter hydrocarbons in gas can evaporate. This process creates gums and varnish that dirty the carburetor, plug fuel passages and prevent gas from flowing into the combustion chamber.

The carburetor bowl below formed corrosion and deposits during storage, which can easily plug fuel passages and prevent the engine from starting.

Storing equipment without stabilizing the gas can lead to deposits that foul the carburetor or injectors.

Ethanol-containing gas can absorb water from the atmosphere, which can lead to phase separation, which occurs when ethanol and gas separate, much like oil and water. Ethanol that has absorbed enough moisture and has sat long enough can foul the fuel system and prevent the engine from starting.

No matter how many times you yank the pull cord and pollute the air with your advanced vocabulary, the lawnmower won’t start if it’s trying to run on bad gas.

In extreme cases, evaporation of lighter hydrocarbons can change the gasoline’s composition enough to prevent it from igniting. The gas may be fueling the engine, but it doesn’t matter if it won’t ignite.

Bad Gas in Your Lawnmower? Here’s How to Fix It

If you neglected to add gasoline stabilizer to the fuel prior to storage, empty the tank and replace with fresh gas. If the tank is nearly empty, simply topping off with fresh gas is often enough to get it started.

On some mowers, you can easily remove and empty the fuel tank. Sometimes that’s more trouble than it’s worth. In these cases, use a fluid extraction pump or even a turkey baster to remove the bad gas. You don’t need to remove all of it; but try to get as much out as possible.

Clean the Carburetor

You’ve replaced the fuel, but your lawnmower still won’t start.

Next, try cleaning the carburetor. Remove the air filter and spray carburetor cleaner into the intake. Let it sit for several minutes to help loosen and dissolve varnish and gums.

Remove the air filter and spray carburetor cleaner into the intake. Let it sit a few minutes to loosen deposits.

On some carburetors, you can easily remove the float bowl. If equipped, first remove the small drain plug and drain the gas from the bowl. Remove the float bowl cover and spray the float and narrow fuel passages with carburetor cleaner.

This kind of “quick-and-dirty” carburetor cleaning is usually all it takes to get the gas flowing again and your lawnmower back to cutting grass.

If not, consider removing the carburetor from the engine, disassembling it and giving it a good cleaning. Be forewarned, however: taking apart a carburetor can lead to nothing but frustration for the uninitiated. Take pictures with your phone to aid in reassembly. Note the positions of any linkages or the settings of any mixture screws, if equipped. If you’re at all reluctant, visit the servicing dealer instead.

Consider replacing the carburetor altogether. It’s a fairly simple process on most smaller mowers and it’s often less expensive than taking it to the dealer.

Direct compressed air from the inside of the air filter out to remove debris that may be reducing airflow and preventing the lawnmower from starting.

Clean/Replace the Air Filter

With the air filter removed, now’s the perfect time to clean it.

Tap rigid filters on a workbench or the palm of your hand to dislodge grass clippings, leaves and other debris. Direct compressed air from the inside of the filter out to avoid lodging debris deeper into the media.

Use soap and water to wash foam filters. If it’s been a few years, simply replace the filter; they’re inexpensive and mark the only line of defense against wear-causing debris entering your engine and wearing the cylinder and piston rings.

An incorrectly gapped spark plug can prevent the engine from starting. Set the gap to the specification given in the owner’s manual.

Check the Spark Plug

A dirty or bad spark plug may also be to blame. Remove the plug and inspect condition. A spark plug in a properly running four-stroke engine should last for years and never appear oily or burned. If so, replace it.

Use a spark-plug tester to check for spark. If you don’t have one, clip the spark-plug boot onto the plug, hold the plug against the metal cylinder head and slowly pull the starter cord. You should see a strong, blue spark. It helps to test the plug in a darkened garage. Replace the plug if you don’t see a spark or it appears weak.

While you’re at it, check the spark-plug gap and set it to the factory specifications noted in the lawnmower owner’s manual.

If you know the plug is good, but you still don’t have spark, the coil likely has failed and requires replacement.

Did You Hit a Rock or Other Obstacle?

We’ve all killed a lawnmower engine after hitting a rock or big tree root.

If your lawnmower won’t start in this scenario, you probably sheared the flywheel key. It’s a tiny piece of metal that aligns the flywheel correctly to set the proper engine timing. Hitting an immovable obstacle can immediately stop the mower blade (and crankshaft) while the flywheel keeps spinning, shearing the key.

In this case, the engine timing is off and the mower won’t start until you pull the flywheel and replace the key. It’s an easy enough job IF you have a set of gear pullers lying around the garage. If not, rent a set from a parts store (or buy one…there’s never a bad reason to buy a new tool) or visit the dealer.

My Lawnmower Starts But Runs Poorly

If you finally get the lawnmower started, but it runs like a three-legged dog, try cleaning the carburetor with AMSOIL Power Foam. It’s a potent cleaning agent designed to remove performance-robbing carbon, varnish and other gunk from carburetors and engines.

Add Gasoline Stabilizer to Avoid Most of These Problems

Which sounds better? Completing all these steps each year when your lawnmower won’t start? Or pouring a little gasoline stabilizer into your fuel tank?

Use a Good Motor Oil for Your Lawnmower

Although motor oil has no bearing on whether your lawnmower starts or not (unless you don’t use oil at all and seize the engine), it pays to use a high-quality motor oil in your lawnmower.

This is especially true for professionals or homeowners running expensive zero-turn or riding mowers.

Lawnmower engines are tougher on oil than most people realize. They’re usually air-cooled, which means they run hotter than liquid-cooled automotive engines.

They often run for hours in hot, dirty, wet conditions. Many don’t have an oil filter, further stressing the oil.

In these conditions, motor oils formulated for standard service can break down, leading to harmful deposits and reduced wear protection.

For maximum performance and life, use a motor oil in your lawnmower designed to deliver commercial-grade protection, like AMSOIL Synthetic Small-Engine Oil.

Its long-life formulation has repeatedly demonstrated its ability to safely exceed original equipment manufacturer (OEM) drain intervals in the toughest conditions. It provides an extra measure of protection when equipment goes longer between oil changes than is recommended by the OEM.

Q: I haven’t changed my lawn mower’s oil since last season, so I’m feeling rusty. Remind me: What type of oil can I use in my lawn mower?

A: You’re not alone. In fact, this bit of lawn mower maintenance happens so occasionally that some people forget to replenish lawn mower oil in the first place. It needs replacing after every 20 to 50 hours of operation, depending on your mower’s specifications. If your yard is small, that might mean as few times as once a year! But, while this task is infrequent, it’s also important to change the oil properly—starting with the correct type of oil for lawn mowers—to keep your machine running.

Two types of oil can go into operating lawn mowers, but your mower’s size, type, and capacity might help determine which of these two is the better option. Even the climate you live in can make a difference when the time comes to change or add oil, since each type of oil for lawn mowers has its own recommended temperature range. If you live in a place that frequently heats up to more than 100 degrees, for example, it might be wise to choose an oil made to withstand a wide range of temperatures.

Different Kinds of Lawn Mower Engine Oil

According to a survey of consumers conducted by Briggs Stratton, the world’s largest producer of gasoline engines for outdoor power equipment, 48 percent of those who buy automotive oil for their mower believe that automotive oil and small engine oil are one and the same.

In fact, lawn mower engine oil (as well as oil for other small engines) might actually be the only type your mower can tolerate. Using motor oil meant for a tractor or car can clog and disable some units completely due to its higher viscosity.

Always check your manufacturer’s specifications first. No owner’s manual handy? If yours has a Briggs Stratton engine, you can use the company’s interactive tool to determine the best oil for your specific lawn mower’s engine based on its make and model, motor type, and local climate. Talk about a shortcut! Otherwise, at a minimum, it’s important to keep a few guidelines in mind.

Lawn Mower Oil Types

Not all oils are equal, and it helps to get to know the subtle differences to determine the best oil for a lawn mower and avoid a costly mistake. In general, there are two main types of oil: motor oil and small-engine oil. Brands vary in their formulas, with some being regular oil, some a mix of regular and synthetic and some fully synthetic. Older oils typically were one weight or grade only, but newer oils have a viscosity rating added.

Disadvantages of Gas with than 10% Ethanol:

E10 fuels are approved for usage in lawnmowers. Gas with a higher percentage of ethanol is not recommended. This is because ethanol will absorb water from the air over time, leading to rusting and corrosion, leading to poor performance. Regular gasoline absorbs 50 times less water than E10 gas.

The 2-stroke or 4-stroke engines of lawnmowers are regarded as ‘small engines.’ Ethanol-free gas is best for small engines. Non-ethanol fuel is much less harmful to the engine as compared to ethanol-blended fuel. This is because non-ethanol fuel is not as susceptible to condensation, corrosion, and rust. Most non-ethanol gases are rated at about 89 octane rating, which is good enough for small engines. The reason for using ethanol in gas is because it makes the fuel friendlier for the environment.

High Octane Gas for Small Engines:

Engines with low compression ratios are less likely to benefit from anything unusual in the gas, like a higher octane rating. Some fuels may make your engine harder to start. So, you can use regular gas if you don’t want to spend extra money when your engine can’t even take advantage of it.

The easiest way to check the gas in your engine is to smell the gasoline. Oxidized gas has a strong, pungent smell and is much stronger smelling, unlike fresh gas. The other method is to drain a sample from your machine’s fuel tank or your gas tank into a clear see-through container. If the gas is dark-colored, it has more than likely gone bad.

If you are using mixed gas in your 4-stroke mower, it will show signs of trouble. Oil smoke is the clearest symptom associated with oil burning in a 4-stroke engine.

Related Questions:

What are E0 and E10 Fuel?

E10 is a gas with only 10 percent ethanol. E15 is gasoline with 15 percent, and E85 is a fuel that may contain up to 85 percent of ethanol. The ethanol content of most of the general-purpose gasoline sold worldwide does not exceed 10% by volume. All gasoline engine vehicles can use E10.

How long does gas stay good in a lawnmower?

Depending on the gasoline formula, this degradation can occur in as little as 30 days, though properly stored gas can sometimes stay good for up to a year and up to three years if treated with gasoline stabilizers.

Is ethanol gas harmful to lawnmowers?

Fuels with 10 percent of ethanol content are approved for use in lawnmowers. Gasoline blends containing higher ethanol levels are not. Using fuel with more than 10 percent of ethanol can damage your lawnmower engine and may also void your equipment’s warranty.

How often should I be changing the lawn mower’s oil?

How often you change the oil is dependent on how often you use the lawn mower. It’s always a good idea to replace the oil annually, prior to the start of the cutting season. However, if you’re someone who mows your lawn frequently, takes care of various neighbors’ lawns, or runs a lawn maintenance business, it’s recommended that you change the oil on your walk-behind mower after fifty hours of use. If the size of the job requires a riding mower, or a zero-turn mower, then you’ll want to change the oil after one hundred hours of use.

While the procedure for replacing the oil will differ depending on the type of mower you have and the engine model, for most walk-behind mowers, you can usually unthread the oil tank cap, remove the dipstick, if applicable, and carefully tip the mower to empty the old oil into an approved container. Lawnmower engine oil, like car engine oil, can be recycled at most auto parts stores. Once the oil tank is emptied, return the mower to its upright position, and pour the new oil into the oil fill tube. Walk-behind mower engines usually take 15 oz or 18 oz of oil; riding mower engines require 48 oz or 64 oz of oil. To avoid overfilling, pour in approximately three-quarters of the bottle, then check the tank with the dipstick to determine if the oil level is at full. You can then add more oil, as necessary.