If you’re anything like me, then what goes on inside the average gas-powered engine is a bit of a mystery. While I can take my car to the nearest auto shop whenever something seems off, the same isn’t necessarily true for my lawn mower.
I’m not saying you need to be a small engine expert to operate a lawn mower — quite the contrary. But I do think it helps to learn basic concepts like how to replace a spark plug or change the motor oil.
In this article, I’ll focus on the common problem of getting oil in your lawn mower air filter. I’ll explain some of the reasons this can happen as well as what you can do to fix it at home.
5 Reasons You Got Oil In Your Lawn Mower Air Filter
Though fixing an oil-soaked air filter is relatively simple, you’re better off preventing this issue in the first place.
An oil-soaked air filter can’t do its job of preventing dust and debris from entering your mower’s engine. It’s also possible for a filter to become so clogged with oil that it no longer allows air to enter the carburetor (which is required for an engine to fire).
There are several ways motor oil can make its way into your lawn mower’s air filter, a couple of which involve user error:
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1. Tipping Your Lawn Mower To The Wrong Side
By far the most common way oil gets into a lawn mower’s air filter is when the mower itself is tipped on its side. You may tilt your lawn mower to clear away debris or perform routine maintenance. Either way, there is always a correct direction to tip a lawn mower when accessing its underside.
Anytime you tilt your lawn mower to clear away grass clippings, sharpen the blades, or change out the blades, you want to keep the air filter facing up. This will vary between mower makes and models. Your user manual may explain which direction to tip the machine to prevent getting oil in the filter. If not, you will need to locate the air filter and tilt the mower in the opposite direction.
2. Mower Tilting While on Hills or Banks
Mowing steep hills and valleys is a pain no matter what. Unfortunately, it’s also likely to leak oil into your mower’s air filter.
To prevent oil infiltration in your mower’s filter, I recommend mowing straight up and down, particularly steep hills. If you must mow perpendicular to the slope, be sure to keep the side of your lawn mower containing the air filter pointed up the hill.
The good news is that only the steepest of hills will cause this issue. Most property owners don’t need to worry about the direction of their mower tilts while cutting their lawns.
3. Tilting Mower Whilst Carrying It
Transporting a lawn mower over short distances usually just means pushing it while the engine is turned off. If you need to move your lawn mower to a completely different property or the wheels are not functioning for some reason, however, you may need to pick it up and carry it.
When carrying a push lawn mower by hand, take note of the air filter’s location and ensure it stays above the rest of the motor during transport. Of course, you should also be careful and take any necessary precautions to keep your hands and body away from the mower blades.
If you must haul your lawn mower using a truck bed or trailer, I highly recommend securing the mower with fabric straps. This will prevent the lawn mower from rolling or tipping during transit, which could introduce oil into the air filter.
4. Too Much Oil in Your Lawn Mower
Most lawnmowers require a very small amount of motor oil to function. Overfilling the reservoir makes it far more likely that oil will leak into the air filter or other parts of the engine.
Always reference your mower’s user manual and any markings on the oil reservoir when refilling the engine. Use a funnel and pour the oil slowly. Check the dipstick as you pour to prevent overfilling.
In most cases, you’ll notice obvious signs of excess oil in the engine before the air filter becomes completely saturated. For example, black smoke is a common symptom of oil leaking into the carburetor.
5. Engine Gasket Failure
It’s possible for oil to travel throughout the engine and into the air filter if a gasket or O-ring has failed. This is more common in old lawnmowers with significant wear and tear. If none of the reasons I mentioned above seems to fit your scenario, then engine failure may be the culprit.
It’s hard to diagnose this problem without inspecting (and potentially disassembling) the part of the engine. Even then, you will need considerable knowledge of small engines to determine the exact cause of the leaking oil.
If you determine that a failed gasket is the cause of your soiled air filter, you’ll need to do far more than just replace the filter. Your best option is to reach out to a professional engine repair service or, if the mower is quite old, to invest in a new lawn mower.
How To Fix Lawn Mower Oil in Air Filter
Before handling any part of your lawn mower’s engine, I highly suggest removing the spark plug. This simple step will eliminate any chance of the engine accidentally starting up while you work on the mower.
If you were using your lawn mower when you noticed the problem, then be sure to let the engine cool down before touching it. Donning a pair of work gloves also isn’t a bad idea.
Once your lawn mower is cool and secure, you can remove the existing air filter. If you’re unsure where the filter is located, reference the user manual or look up the mower’s model number online.
It’s important to clean out the air filter casing before reassembling your lawn mower. There may be a layer of oil inside the filter housing or around the carburetor opening.
Drying Paper Air Filters
Unfortunately, no amount of time will dry out an oil-soaked paper air filter. The only way to fix a paper air filter that has come into contact with motor oil is to replace it.
If your lawn mower is fitted with a paper air filter, I recommend keeping a few extras on hand for exactly this occasion.
Washing Foam Air Filters
Some lawnmowers utilize foam air filters. If that’s the case for your mower, you may be able to clean and reuse the existing air filter rather than replace it with a new one.
After you remove the foam filter from its housing, I recommend knocking any large debris loose. Doing this before taking the air filter inside will keep a considerable amount of dirt out of your garage or house.
Wash the air filter in a bucket or basin filled with hot water and regular dish soap. Once all of the oil is removed, rinse the filter with clean water and squeeze out excess moisture with a rag or paper towel.
Even if the air filter now looks brand new, you shouldn’t reinstall it just yet. The filter needs to dry out completely before being placed back inside your lawn mower. My preferred drying method is to lay the filter outside in a sunny location.
Finally, re-oil the filter so that it can easily grab onto dirt and debris passing through your mower’s engine. Be sure to use only fresh oil and do not oversaturate the filter. I prefer to measure out 1 to 2 teaspoons of motor oil — as recommended by The Spruce — for this purpose.
In some cases, washing away all of the oil built up in a foam air filter just isn’t possible. If your mower’s filter still appears soiled, it’s best to toss it and order a replacement instead.
Order a Replacement Air Filter
If your lawn mower has a paper air filter or the foam filter can’t be cleaned, you’ll need to order a replacement. You won’t be able to cut any grass until a fresh, clean filter has been installed in your lawn mower.
Check your user manual for the type of air filter that will fit your lawn mower. You can also reference the old filter — assuming there is a part number printed on the filter that is still visible — if you don’t have access to the user manual.
Many experts recommend ordering replacement air filters from the lawn mower’s original manufacturer whenever possible. Manufacturer filters may offer a better fit than aftermarket products. However, I’ve had good experiences with both kinds. I have looked around several hardware stores and struggled to find the exact model I required. So I suggest removing your air filter, measuring its dimension of it, and searching for it here on Amazon.com. I was amazed at the number of lawnmower air filters available.
While ordering a new air filter for your mower can be a chore, it’s something you should do on a regular schedule. Most lawnmowers perform best when their air filters are replaced at least once a year. According to Briggs & Stratton, foam air filters should be replaced every 3 months. If the old air filter had been serving your lawn mower’s engine for more than one cutting season, it was already past its prime.
Check Your Mower Over
The air filter is not the only part of a lawn mower that oil can end up in. Ideally, you should inspect the entire lawn mower after replacing the air filter to check for other leaks.
The good news is that nearly all problems caused by leaking or excess oil can be easily fixed. You just need to know where to look and how to get things back to working order.
In my experience, the two engine parts most commonly affected by wandering oil are the spark plug and carburetor. Before reassembling your lawn mower and calling it a day, I highly suggest giving these areas a once-over.
Check Your Spark Plug for Oil Contamination
When a spark plug is contaminated by motor oil it is often described as “oil-fouled.” There are several ways this can happen, including when the lawn mower is tipped over and oil spills out of the reservoir.
You should already be removing your mower’s spark plug before accessing the air filter housing. As you do so, be sure to inspect the plug for oil and other signs of buildup.
A spark plug that is otherwise in good shape is relatively simple to clean. I recommend using a piece of steel wool or a soft wire brush to remove any buildup. You may need to use a cleaning solution designed for spark plugs to remove all traces of motor oil. Allow the spark plug to air dry entirely before reinstalling it.
If the spark plug shows serious signs of corrosion, it may be worth replacing it. Check your mower’s owner’s manual for the correct spark plug size before ordering a replacement.
Check for Flooded Carburetor
It’s also possible for motor oil to clog up the mower’s carburetor. The easiest way to fix this is by spraying a carburetor cleaner into the engine. Reassemble the mower and attempt to start it. If it starts successfully, allow the engine to run for a few minutes to help clear out any additional oil buildup.
If your lawn mower still fails to start after following these steps, I recommend reaching out to a small engine repair professional for further help.
SOLVED: Oil on Lawn Mower Air Filter
Oil in your lawn mower’s air filter is a relatively common problem that is quite easy to prevent. If you do accidentally end up with an oil-soaked air filter, however, it’s also easy to fix.
This is a good example of why you should stock up on basic maintenance supplies for your mower and other lawn care tools. I recommend always having a spare air filter as well as extra motor oil and some carburetor cleaner on hand. This little bit of preparation will help you get your lawn mower back up and running as quickly as possible when problems arise.
