How to Change Oil in Lawn Mowers


So you finally have the ultimate lawn care machine.  It cuts the grass with precision.  It mows evenly at faster speeds with a wide deck covering vast swaths of turf with each pass.  It is a well-oiled machine that shines like a trophy in your garage.

Hold it right there.  How are you sure that it is a well-oiled machine?  Unless you have taken specific steps and paid attention to the details, you might just be making an assumption.

A lawn mower is an investment that will provide huge rates of return if you take the time to maintain it properly.  You need to know what kind of oil to use.  Pay attention to the clues the equipment gives you about when you should change the oil in a lawn mower. 

These are just a few considerations that go into what should be the regular maintenance of a mower.  And just knowing that you need to change the oil is not nearly enough.

Regular maintenance and care of this piece of machinery will extend its life and help it perform just as it did the first time you used it.

A new-looking lawnmower that is well maintained and ready to keep cutting grass

Keep reading to learn all the things you need to know about changing lawn mower oil and proper upkeep to ensure that it continues to sculpt your lawn into the point of pride it has become for you.

What Kind of Engine Does Your Lawn Mower Have

To know what kind of maintenance is necessary for keeping your motor running, you have to know what type of engine is driving the machine.

Most mowers nowadays have four-stroke engines.  These engines are capable of burning regular gasoline straight from the pump.  They also require oil to be added to the motor’s crankcase to lubricate the moving parts inside.  This lubrication prevents corrosion and friction.  Over time, oil in these engines will break down and lose their viscosity and must be changed.

Two-stroke engines have a different internal process than four-stroke engines.  Part of these differences is how the pieces of the engine are lubricated.  The crankcase on a four-stroke engine is closed and, as such, requires the oil to be added externally.  In a two-stroke engine, the crankcase is used as part of the induction tract. As such, it requires that oil be mixed with the gasoline instead of being added separately.

So, in a two-stroke engine, you are actually changing the oil every time you have to put fuel in to run it.

Conversely, a four-stroke engine uses the same oil to lubricate the engine over an extended period of time and requires that you change the oil when it has broken down far enough.

Changing the fuel, concurrently also changes the oil in a two-stroke engine lawnmower. This picture shows someone pouring fuel into a red lawn mower.

When Should You Change the Oil in Your Lawn Mower

Several factors come into play regarding how often the oil should be changed in your machine.

At a bare minimum, you should change the oil at the end of every mowing season.  To keep your mower in top condition, experts recommend that the oil is changed between 20 and 50 hours of use.

That is a pretty big window of time, though.  So you can consider some other factors when determining where your lawn mower falls in that time spectrum.

The first consideration is how often you are mowing the yard.  If you are in an exorbitant growing season and you find it necessary to mow every four days, the oil will have to be changed a bit more frequently than if you are mowing every ten days or so.

It also depends on the conditions of your yard.  If your property has rougher terrain, bits of debris, or small rocks, then you will probably fall closer to the 20-hour end of that scale.  If your lawn is pristine and flat, then you won’t find more frequent oil changes necessary.

Lawns with lots of debris and rock can make your lawn mower go through more wear and tear. This image is a rocky lawn with two bags full of sand.

Another factor that determines oil change frequency is your specific geographic region and its climate.  Hotter weather can be rougher on equipment and will require less time between maintenance sessions. 

When new oil is put into the crankcase, it is golden or amber in color.  Over time it burns up and breaks down and turns deep brown or black.  You should check the oil level before each use. If the oil on the dipstick is black or brown you know that your lawn mower oil needs to be changed.

For lawn mowers that are brand new off the showroom floor, the oil should be changed immediately following the fifth hour of use.  This is because the movement of the new pieces of the motor will leave metal filings in the oil.  If you leave these shavings in the oil, then you run the risk of excessive and unnecessary wear and tear on your engine.

What Kind of Lawn Mower Oil Should You Use

There are generally three different types of oil that are suitable for use in your lawn mower.

SAE 30 is the most common type of oil used in small engines like the one on your lawn mower.  It is also ideal if you experience warmer temperatures in your area.

SAE 10W-30 can be used in areas with varying ranges of temperature.  This type of engine oil will improve your ability to start in colder weather.  One drawback of SAE 10W-30 is that it can increase your engine’s overall oil consumption.

SAE 5W-30 is a synthetic lubricant that offers your engine the best protection at all temperatures.  It improves starting capability in colder weather and will not be consumed by your engine as fast as the others.

Steps to Changing the Oil in Your Lawn Mower

There are some things you should know about changing the oil in lawn mower machines and equipment.  Follow these guidelines for changing the oil in a lawn mower safely and effectively.

A lawn mower that is cutting grass with clippings coming out from the back.

Preparing to Change the Oil

You should make sure you gather everything you need to change the engine oil in your lawn mower beforehand.  This will make it easier for you while you are changing your lawn mower oil.  Here is a list of what you will need:

  • Owner’s Manual
  • Shop rags
  • The recommended new oil for your mower
  • Oil pan
  • Funnel
  • Cardboard or old newspaper
  • Proper container for safe disposal of the old oil
  • Socket wrench
  • Pipe wrench or filter wrench
  • Jack or automotive ramps for riding mowers

Once you have collected everything you need for the oil change, you should start your mower up and allow the engine to run for a few minutes before you begin.

Allowing your engine to warm up the oil and circulate before you change oil will remove debris from the engine.

You should always make sure to disconnect the spark plug wire before the oil change.  When you disconnect the spark plug wire, you ensure that your mower will not accidentally start while you are working on it.

You can remove the spark plug entirely if it makes you feel more comfortable.  This is a sure-fire way to make sure your engine doesn’t fire up.

Drain the Old Oil From the Engine

If you have a push mower, you should prop the mower up, so the exposed spark plug faces upwards.  For riding mowers, use a jack or automotive ramp to give you access to the area of the engine where the drain plug is located.

Spread the newspaper or cardboard underneath the mower and place the oil pan directly underneath the drain plug. 

Using a socket wrench, loosen the drain plug (it is not necessary to remove it entirely) until it begins to drain the oil from the engine into the oil pan.  Drain the oil until it slows to a single drip that falls at least 4 or 5 seconds apart.

Transfer the old oil from the oil pan into a proper container.  Set the old oil to the side so that you can take it to your local oil recycling facility to be disposed of properly.

Tighten the drain plug on your engine once you drain the oil.

Someone draining old oil from a lawnmower that is propped up.

Change Oil Filter

Oil filters keep the oil from being infiltrated by larger pieces of dirt and debris.  If debris is allowed through the filter, it will cause excessive engine wear to your mower.

While the filter may not require changing every time you change the oil, it does warrant checking it every time. 

A good rule of thumb is that you should change the filter at least once a year, but this is a basic guideline.  Refer to your owner’s manual for information about the frequency at which you should change the oil filter specific to your piece of equipment.

Once you have located the oil filter, use your hands or the pipe/filter wrench to remove the filter from the engine.

After you have removed the filter, you should clean the area where the filter attaches to the mower (called the adaptor) as well as the seal on the new oil filter.

Wipe some new engine oil onto a shop rag and lubricate the seal on the new filter.  Place the new oil filter onto the adaptor and tighten into pace using the pipe/filter wrench or your hands.

Adding oil to a red lawnmower

Refill the Engine With New Oil

Locate the oil fill plug on your engine and remove it.  Clean the area around the plug so that you avoid the infiltration of your engine.

Place the funnel into the engine where you have removed the oil fill plug and pour the amount of oil recommended by your owner’s manual into the crankcase.  Be careful not to overfill as this can cause the motor to stop running.

After you have filled the crankcase with the recommended amount, you need to replace the oil fill plug.  Take the clean dipstick and place it down into the dipstick shaft and remove it to ensure the oil level in the motor is correct.

Lastly, replace the dipstick in the shaft and clean up any excess oil that may have spilled on or around the lawnmower.

Someone checking the dipstick to make sure you have filled with the right amoint of oil

Clean Up

After the oil is changed, you should clean up the area where you worked on your equipment. 

Replace the spark plug and reconnect the spark plug lead wire to the engine.  To ensure that you have reconnected the spark plug and its lead wire correctly, fire the engine up.  This will also circulate the oil in your engine.

Additional Steps For Complete Maintenance of Your Machine

Changing the oil is a crucial step to maintaining your mower.  However, there are some other things that you can do to extend the life and efficiency of your equipment.  Once you have changed the oil, lawn mower machines need the additional steps that follow here. Keep your law mower well maintained and you will make the process of lawn care so much easier!

  1. Clean the deck each time you mow
  2. Clean and replace the air filter as needed
  3. Replace the spark plug as needed
  4. Clean out the carburetor
  5. Maintain correct tire pressure
  6. Winterize your machine
  7. Drain the gas from the tank
  8. Disconnect the spark plug wire
  9. Remove the blades for sharpening

The Green Pinky

About the author: Jeffrey Douglas is a horticultural hobbyist that loves everything related to plants and gardening. He specializes in gardens and houseplants. Read More

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