A Guide to Washing Your Lawn Mower Engine

Investing in a high-quality lawn mower is essential in keeping your property looking pristine. As purchasing a new lawn mower is no small outlay, it is essential to take the necessary steps to preserve the mower’s engine life as long as possible. However, with the amount of debris your mower will accumulate with just a single pass through your lawn, this is no small task, with regular cleaning efforts required to keep the mower functioning at its peak performance. 

Most recommendations call for the mower engine to be cleaned after every 25 hours of use, meaning that you are looking at a couple of cleaning sessions per year. To assist in this regard, the following guide can help you with all aspects of washing your lawn mower engine and keeping it clean for years to come. 

washing your lawn mower engine

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When is it Time to Wash a Lawn Mower Engine?

Perhaps you have recently purchased a used mower, or your mower has been sitting in storage for a long time, and you are not really sure if the engine is dirty or not.

It is recommended to clean your lawn mower engine every 25 hours of use. Cleaning your engine will help prevent significant engine damage due to debris buildup, dirty air filters, and contaminated oil.

The following are some common symptoms of a mower engine that needs to be cleaned. While these symptoms may indicate a larger issue, it does not hurt to at least give cleaning the engine a try first before taking the mower to a small engine mechanic.

Visible Debris on the Exterior of Lawn Mower Engine

Although a dirty exterior does not necessarily mean that the engine will be dirty, it is a safe bet that if excess grime has visibly built up on the outside of the mower, then some of that debris will make its way to the interior, as well.

Therefore, it is always best to start any engine clean by removing all exterior debris and ensuring that none of it can get lodged into hard-to-clean areas of the engine during the cleaning process. 

Difficulty Starting Lawn Mower

For an engine to start, there must be air, fuel, and a spark. Without one of these components, the mower is as good as dead.

For heavily soiled engines, it is likely that airflow is greatly restricted, preventing the engine from igniting. Give the engine a thorough clean and see if it solves your starting issues.

Increased Lawn Mower Fuel Consumption

If you notice that a tank of gas is not getting you as far around your yard as it used to, it is possible that a dirty engine could be the problem. Your engine could be consuming more fuel to make up for the lack of airflow and maintain production, so see if cleaning your engine results in better fuel economy. 

Lawn Mower Power Loss

When your mower engine gets dirty, the air filter works as a buffer to ensure that no contaminated air is cycled into the combustion chamber. However, after heavy exposure to debris, the air filter can lose its effectiveness.

If you notice your lawn mower sputtering or simply not operating at its normal power, it could be the result of too much run time with a dirty engine.

Soiled Air Filter in Lawn Mower

As mentioned in the previous section, the air filterOpens in a new tab. works to ensure the quality of air entering the combustion chamber. When it gets too dirty, inadequate airflow will result.

Therefore, one of the simplest ways to tell whether or not your mower’s engine needs cleaning is to check the condition of the air filter. In proper condition, the air filter should have white sheets with few specks of dirt present. Once the filter itself starts to get brown or discolored, or it simply becomes heavily caked in debris, then it is time to wash your mower engine and replace the air filter.

Excess Engine Oil In Lawn Mower Engine

There are many reasons why you should never overfill your mower’s oil chamber. However, one of the most pertinent is that it can cause rapid grime buildup.

The extra oil must go somewhere, and it usually leaks back into the engine. This makes it easy for cut grass and dirt to readily stick inside the engine. As a result, if you see oil anywhere outside of the reservoir, make sure that the oil reservoir is sitting at appropriate levels and wash your engine.

Excessive engine oil can cause significant engine damage as we explain in, “This is What Happens If You Put Too Much Oil In a Lawn Mower“.

Black Smoke from Lawn Mower

Black smoke is never a good sign when dealing with engines. Although there is a chance that it is the symptom of a more serious problem that could require the attention of a small engine professional, try giving it a clean and see if it is the result of grease and grime buildup in the engine.

5 Reasons Your Lawn Mower May Be Smoking

How to Wash Your Lawn Mower Engine

The process of washing your mower engine is not particularly difficult, but care must be given to avoid damaging the engine, especially when using air compressors or pressure washers. Use the following steps to help guide you through the process:

  • Remove any large particles. Before getting to work on the engine, it is essential to give the mower a general clean using your hands. Brush away any large clumps of grass or other pieces of debris that may be a threat to nestle down into the engine once you start cleaning more meticulously.
  • Disconnect the spark plug lead. Disconnect the spark plug lead and secure it away from the spark plug. You do not want the spark plug lead to inadvertently touch the spark plug during cleaning (this presents a serious safety risk), so do not be haphazard in this step.
  • Remove the engine screen or shroud. Not all mowers will have a shroud or engine screen, so this step may not be necessary. However, if there is a screen, you will want to remove it for increased access to the engine for improved cleaning ability.
  • Disconnect the blower’s housing. If the housing is plastic (typical with most newer models), it can be snapped off. If the housing is metal, a set of screws or bolts will need to be removed too before the housing can be taken off.
  • Clean any interior components. Use a small bristle brushOpens in a new tab. to clean the cooling fins, the inside of the blower housing, and the flywheel fins. Scrape away the debris gently, taking care not to damage the housing or flywheel. For any particularly tough dirt or grime buildup, apply a light solvent to the brush before scraping.
  • Clean the flywheel cutting screen. Debris accumulation on the flywheel cutting screen can lessen the engine’s ability to cool itself. Use your brush to clean this screen thoroughly.
  • Clear the engine of loose debris. Try to clear as much loose debris as possible using only your hands. If you want to be more thorough, you can use an air compressorOpens in a new tab. or pressure washerOpens in a new tab. to blow away the remainder. However, you must use these tools at very low pressure settings to avoid blowing debris into less accessible parts of the engine. If using a pressure washer, also give the engine thorough time to dry completely.
  • Check the governor linkages. Thoroughly clean the governor linkages, including the pneumatic governor vane (if applicable). Check to see that the linkages are moving freely, and use a light solvent to remove any grime that may prevent smooth motion.
  • Check the brake assembly. Look for debris around the brake assembly and make sure that the brake cable and linkage are moving freely.
  • Reconnect the blower housing and spark plug. Make sure that the blower housing is snapped or screwed back in place correctly, and connect the spark plug lead back to the spark plug.

Can I Power Wash My Riding Mower Engine?

For a larger riding lawn mower, the most convenient way to clean the engine is with a pressure washer. This is definitely a solid option that can cut down significantly on cleaning time. 

When cleaning with a pressure washerOpens in a new tab., it is essential to remember to disconnect any electrical components that may get shorted out by water and take care that high-pressure settings do not lodge debris deeper into the engine’s hard-to-reach locations.

Cleaning all components of the mower, even those not directly associated with the engine, is important, as dirt and debris can make their way into the engine and affect performance. 

Use the following steps to clean your riding mower with a power washer:

  • Remove visible debris. As with any type of engine cleaning, clear as much large and visible debris as possible from the exterior.
  • Disconnect the spark plug lead. Disconnect the spark plug lead and secure it away from the spark plug. This is a critical step when using a power washer, as you do not want the water to cause an electrical shortage.
  • Elevate the mower. You will need some type of jackOpens in a new tab. to access the underside of the mower. A top-side approach is not sufficient, so you cannot afford to skip this step, as it is essential to clean the mower from all angles. When selecting a jack, make sure that it can elevate to an appropriate height (at least a foot).
  • Remove the lawn mower blade (optional). This is an optional but recommended step. Removing the blade can help ensure safety during the power wash. However, it may be a little challenging to remove the blade from a riding mower, so if you choose to wash without removing the blade, just exercise extra caution and avoid getting too close.
  • Clean the bottom of the mower deck. Use a multi-purpose solution to spray the bottom of the mower deck. Start at the top of the deck and work your way down, using a gentle, mist-type spray setting. Allow the solution to sit on the mower deck for 5 to 10 minutes.
  • Rinse away debris. After you have allowed the cleaning solution to work, rinse the underside of the deck with a gentle spray pattern, using the same top to bottom pattern used for applying the solution, making sure that the spray nozzle does not come closer than six inches to the mower.
  • Set the mower upright. After the underside of the mower has been cleaned, reconnect the mower blade, if applicable, and lower it from the jack to return it to an upright position.
  • Open the hood (if applicable). While some riding mowers have the engine directly accessible, others house the engine beneath a hood, similar to a car engine. If this is the case for your mower, lift the hood to expose the engine.
  • Apply a degreaser. Much of the grime directly on the engine will be the result of debris mixing with oil buildup. Use a pressure washer-safe, heavy-duty degreaser and gently spray the engine with this agent. Allow the degreaser to work for 5 to 10 minutes. 
  • Rinse the grime away. Start with a low-pressure spray pattern. Spray from a distance, making sure not to wash away any decals or sensitive engine parts. If you need to increase the cleaning power, keep the pressure at the same setting and carefully move closer to the engine. Give extra attention to areas susceptible to heavy buildups, such as the discharge chute.
  • Allow the mower to dry. It is best to power wash the mower engine early in the day, as it will give ample time to dry thoroughly. After it is dry, reattach the spark plug lead and close the hood (if applicable).

Setting Up a Pressure Washer to Wash a Lawn Mower Engine

When preparing to clean your mower engine with a pressure washerOpens in a new tab., it is essential to correctly set up the pressure washer to ensure the best chance for success. The following steps can help you in that regard:

  • Familiarize yourself with the instructions. Each pressure washer will be a bit different, so it is important to familiarize yourself with the ins and outs of each specific model. Of most importance is to have a clear understanding of what kinds of solutions with which the power washer is compatible.
  • Place the power washer near a water supply. Make sure that the water supply falls within the washer’s specifications. Pressure washers will be rated to pump a certain number of gallons per minute.
  • Carefully connect the spray gun, pump, and hose.
  • Connect the machine to a garden hose. Make sure the pressure washer is sitting on level ground during this step.
  • Turn on the pressure washer. This will let out any excess air. Power the machine off before connecting the nozzle.
  • Connect the nozzle. Remember that you want to use a gentle spray nozzle that does not concentrate its power too heavily in one specific location, as this can damage delicate parts of the mower engine. Make sure the nozzle is properly attached to the spray gun.
  • Turn the pressure washer on again. Turn on the machine, put the throttle on “high,” and switch the choke lever to “run.” You are now ready to start the engine of the machine.
  • Grip the starter handle. Slowly pull the starter handle until you feel it starting to get heavy. Once the handle gets heavy, pull hard.
  • Return the starter handle. Place the starter handle back in its original position.
  • Prepare to start the wash. Now that the pressure washer is up and running, you are ready to wash your mower engine. Ensure the spray gun is facing away from you, press the red button to unlock the trigger, hold down the trigger to release the pressure, and begin spraying.

How to Degrease a Lawn Mower Engine While Washing

As grease buildup is one of the most significant threats to a mower engine, some specific tips can help you remove any troublesome grease buildup as you clean your lawn mower engine.

Before starting the process, be sure that your power washer can run the type of solution you are set to use. Also, be sure to check that any degreasing agents will not corrode or damage the mower engine in any way. If both of these boxes are checked, the following steps can help you to most thoroughly clean the mower engine:

  • Situate your mower and pressure washer. They should be in a well-ventilated area, close to the necessary water supply. An outdoor lawn is generally the best option.
  • Apply a degreasing agentOpens in a new tab.. With the mower engine off and the spark plug lead disconnected, gently spray the degreasing agent to heavily crusted surfaces.
  • Wait for the agent to work. Give the degreaser about 15 minutes to break down dirt and grime.
  • Wipe away residue. Use a microfiber clothOpens in a new tab. to wipe away as much residue as possible.
  • Rinse away the remaining debris. Remove the degreasing agent from your pressure washer and cycle through clean water. Gently wash away any debris that you cannot reach with the towel. Give the engine ample time to dry before reconnecting the spark plug lead and returning your mower to storage.

Using Cleaning Solutions for Lawn Mower Engines

Using cleaning solutions, such as the degreasing agent mentioned above, can make cleaning your mower engine with a pressure washer more efficient. However, added precautions must be taken when using these types of products. Consider the following bits of advice when attempting to use cleaning solutions with a pressure washer for cleaning your mower engine:

  • Read the manuals. Know all of the specifics regarding both your mower engine and pressure washer. Make careful note of any products that cannot be used with either.
  • Locate the injection system. Your pressure washer will have a cleaning solution injection system to easily mix the solution with water. Locate this area on your pressure washer before adding the solution. Some washers even have on-board storage tanks for added convenience.
  • Check the solution. Many types of solutionOpens in a new tab.s can be used in a pressure washer. Ensure that the label says that it is compatible with pressure washers before introducing it to your system. Never use bleach or bleach-based products, as they can damage your mower engine and washer pump and kill surrounding vegetation.
  • Add the solution to the pressure washer. Some solutions will be ready to use, meaning they can be added directly to your pressure washer. Other solutions are concentrated, so you must use a bucket or can to mix the concentrate with the appropriate amount of water before adding it to the pressure washer.
  • Connect the hose to the pump. If your pressure washer does not have an on-board storage tank, connect the solution hose from the solution reservoir to the pressure washer solution pump. If it has a storage tank, ensure that the valve connecting the solution to the pump is turned to the “on” position. 
  • Attach a low-pressure soap nozzle. Pressure washers will only cycle cleaning solution in low-pressure mode, which is ideal for cleaning mower engines. Use a low-pressure soap nozzle before applying the solution. 
  • Apply, wait, and rinse. Use a gentle top to bottom motion to apply the solution to your mower engine so that any debris that breaks loose is not washed back onto a clean area. Wait between 5 to 10 minutes to allow maximum cleaning effectiveness for the solution. Use a rag first and gently rinse any remaining debris free with water, allowing the engine to dry.

Important Reminders When Washing Your Lawn Mower Engine

Although regularly cleaning your lawn mower engine is of utmost importance in ensuring its useful life, there are a few crucial pieces of advice to keep in mind any time you clean your machine—and especially when a power washer is involved:

Safety First

A mistake made when performing maintenance work on a lawn mower can result in serious injury. As a result, safety should be the number one priority when attempting to wash your engine. The following are a few tips to help ensure safety during the process:

  • Disconnecting the spark plug leads not only helps prevent electrical shortages, but it makes it impossible for the lawn mower to start unexpectedly.
  • Be familiar with the safety guidelines as outlined in the owner’s manual.
  • Work in a well-ventilated area.
  • Work on a firm, flat surface to prevent the lawn mower from moving unexpectedly during cleaning.
  • If cleaning a riding mower, ensure that the parking brake is engaged.

Avoid Electrical System Components

When using a pressure washer, take extra care to avoid any electrical components. Getting the wrong electrical parts wet can cause shortages that will prevent your mower from working correctly. In a best-case scenario, parts can be replaced after a shortage; in a worst-case scenario, the entire electrical system may be undermined.

Avoid Bearings

Do not spray your pressure washer directly into bearings. The pressure may cause damage that will cause the bearings to seize and cause your engine to malfunction.

Wash Early in the Morning

It is always best to pressure wash your mower early in the day, specifically on days when ample sun is in the forecast. As your mower needs to be completely dry before spark plug leads are reattached, and the mower is put into storage, starting early in the day will give it the most time to dry thoroughly. 

Tips for Maintaining Your Lawn Mower Engine

As with any piece of mechanical equipment, there are some helpful tips to help ensure the health and longevity of your mower engine:

  • Wash as recommended. The standard is to wash the engine after every 25 hours of use. However, more frequent cleanings may be necessary if you use your mower for particularly heavy-duty projects that introduce it to a lot of dust and debris.
  • Remove big debris after each use. Although you do not have to clean the engine after each use, it is essential to clear any visible debris from the exterior of the mower. Even if you think it will not affect the engine, keeping your mower in close contact with debris presents the opportunity for it to seep into more delicate areas of your mower.
  • Store indoors. Whenever possible, keep your mower stored indoors, preferably in a garage or machinery shed. Wind is one of the best ways to introduce debris to the mower engine, so keeping it out of the elements can help make your cleaning efforts easier.
  • Empty the gas tank. When storing your lawn mower over the winter, empty the gas tank. Old gas can turn stale, gumming up the carburetor and providing a breeding ground for rust in the engine.
  • Disconnect the spark plug. One of the most important tips for washing the mower engine, it is also a good idea to disconnect the spark plug lead any time you plan on letting your mower sit for an extended period. This will prevent the machine from starting unexpectedly. 


A lawn mower is an expensive piece of equipment that every homeowner must have to maintain the curb appeal of a property. To protect the investment, it is essential to wash the lawn mower engine with regularity. If you own a lawn mower but are unsure as to how to clean the engine properly, use the helpful advice outlined in this guide to keep your mower engine clean and functioning at its fullest capacity for years to come. 

Powered Equipment Team

We're just a guy and a girl obsessed with outdoor power equipment! We are excited to share the knowledge and tips we have learned over our combined 55 years in the power equipment industry. We have both ran equipment dealerships and took pleasure in helping our customers everyday providing equipment repair, parts, purchasing, and business tips to our residential and commercial clients. We hope our blog will help you with your next purchase, repair, or project.

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