Your air filter is super important in ensuring your gas mower runs smoothly. It’s there to let the right amount of air into the engine, without also letting in dirt and grime that could impair its performance and potentially cause long-term damage.
So if yours is absolutely soaked in oil, you can probably guess that it’s not going to do its job right, and that it’s not something you can just leave to “wait and see what happens”. Things are not going to improve. In fact, it’s quite likely that your mower won’t start until you take action.
A lawn mower air filter soaked in oil will have to be removed and then replaced with a new one 95% of the time. With foam filters, it might be possible to clean it.
Lawn Mower Air Filter Soaked in Oil: Here’s What to Do
Before we get into the weeds, I will just say that you shouldn’t freak out if you find your air filter is soaked in oil. Yes, it is a bit of a mess. But your mower is not ruined, and it really is quite an easy and affordable fix. Here’s what you’re going to want to do:
Safety First – Always
Any time you’re doing some maintenance on your mower, you should always take certain precautions. Here’s what I recommend:
- If you’ve been using it, let it cool down – laying your hands on a mower if the engine is still hot from running is a bad idea. Leave it outside for a few minutes and let it cool off before you start work.
- Disconnect spark plug – This is so important and might save your fingers someday. As long as the spark plug is connected, there’s always a chance the mower could fire up. It shouldn’t, but in theory, it’s possible. Make it impossible by disconnecting the spark plug now.
- Wear gloves – This isn’t an absolute must, but when I’m going to come into contact with any chemical – oil, gasoline, etc – I prefer to put some thin protective gloves on. Latex gloves work well.
Now…Dealing with that Oil Soaked Filter
Air filters in lawn mowers are not all the same. They vary from manufacturer to manufacturer, but in general, there are two main types. And the steps you should take do depend somewhat on which type of filter your mower uses.
Paper Air Filters
If you’re dealing with a paper filter, it’s simple. You have just one choice – to replace it. There’s no way you’re cleaning a paper lawn mower air filter soaked in oil. Don’t even try. You probably have more chance of digging to the earth’s core with a shovel.
If you have some replacement filters on hand, great. If not, you’re going to have to get some. I’d always recommend going with the manufacturer-specific ones as opposed to the “universal” ones that are sold. They generally work better IMO.
While you don’t need to do anything to the filter itself other than fit it, you are going to want to clean any oil from the casing. You’re probably going to want to remove the air filter housing and remove any oil from the carburetor opening too.
Sometimes, even when you replace the filter, your mower won’t start. Normally, it’s because oil is blocking the carburetor. If you spray a bit of carburetor cleaner into the throat of the carburetor, and then try to get your mower going, this will often clear the rest. Don’t be alarmed if you see black smoke coming out of the mower for a while. That’s just the oil residue being burnt off.
Foam Air Filters
There’s a small chance – and it is a small chance – that you might be able to salvage your filter if it’s made from foam. It really depends on how bad the situation is.
But to not be wasteful, it’s always worth trying to clean a foam filter that’s soaked in oil before you wave the white flag and go out and buy a new one.
The process is super simple.
- Knock off any debris. This will be hard if it’s super soaked, but if you haven’t changed/cleaned your filter for some time, there’s likely going to be a buildup of debris on the top side of the filter. Knock this off while you’re still outside, or into a garbage bin.
- Take it to the sink. Now you’re going to want to take the filter to a sink and you’re going to use some good old hot water and dishwashing liquid. Give it a thorough clean, trying to get all of the oil off. If you manage to do that, rinse it to remove all of the soap.
- Squeeze out all of the moisture. Once you’re done cleaning, give the filter a really good squeeze to drain as much of the moisture out as possible. On the final squeeze, it can be helpful to wrap it in some paper towel, as this helps soak up even more of the water.
- Leave it in the sun. Now it’s just a waiting game. You need to let the filter completely dry out. And the best way to do this is to leave it in the sun.
If you do all of this and it comes out clean – you’re golden. You can now just add some oil to the filter (yeah – kind of ironic given the topic we’re covering here, but foam filters do need to have a small amount of oil soaked into them), reseat it back into its casing, replace the cover and you’re good to go.
If you attempt to clean your air filter, but the oil just isn’t coming out and it remains clogged, you’re going to want to source a replacement (as with paper filters, I would advise you to go with a manufacturer-specific one if you can), clean out the casing and fit the new filter.
Other Things to Check If Your Air Filter is Clogged with Oil
If you remedy the oil soaked air filter, but you still have issues with starting your mower afterward, there are a few other things you can check. I would advise you to do these things anyway to be honest, since it’s possible other parts of your mower might have been compromised, especially if you determine the cause of your oil problem as being your mower was tipped on the wrong side.
If the combustion chamber is flooded with oil and/or gas, it’s possible that the spark plug may be contaminated. You’re going to want to remove it and give it a quick clean with a soft wire brush. And do make sure you use a soft brush, as harder wire brushes may damage the porcelain insulator around the electrode. And that wouldn’t be very clever!
After you’re done cleaning it, leave it to air dry before replacing it.
The other fairly common reason why your lawn mower might not start after an oil problem is that oil is either completely or partially blocking the carburetor. You’re going to need to try and remedy that.
There’s an easy/lazy way (which I touched on a bit earlier) to clean a lawn mower carburetor without removing it, and then a harder/more involved way. If you’re like me, you’ll probably try the lazy way first and then go for the other option only if necessary.
Okay, so you’re going to need some carb cleaner for this. All you’re going to do is spray some of this in the throat of the carburetor, and then you’re going to attempt to start your mower. If you can get it started, this will usually clear the rest. It might not run as smoothly for a few minutes, but should sort itself out the longer you run it.
If this doesn’t work, you’re going to need to remove the carb to give it a more thorough cleaning (here I explain how to clean a lawn mower carb this way). This is definitely more involved, and if you’re not someone that likes to play around with these sorts of things, you might want to ask someone with a bit more knowledge/experience.
Most Common Causes of a Lawn Mower Air Filter Soaked in Oil
There are a few different potential reasons why you might find yourself staring down at a lawn mower air filter soaked in oil. We’re going to run through them quickly below.
Turning Your Mower on the Wrong Side
This might be a revelation to some of you, but there is in fact a right way and a wrong way to tip your lawn mower. And an oil soaked air filter is what can happen if you tip your mower the wrong way. It’s a mistake that I see time and time again, particularly among those that don’t have too much experience with mowing the lawn. They tip their mower over to tighten/sharpen/change their blade, and halfway through find a messy surprise.
The position of the air filter can vary depending on the make and model of mower that you have. But when you tip it on its side, the air filter should always be pointing upwards. If it’s pointing downwards, you’ve got the gas and oil up in the air, and gravity is going to do the rest.
Mowing on Extremely Sloped Land
Now this doesn’t happen often and won’t apply to most people, but I have heard of it being responsible for oil leaks in mowers, so thought I’d mention it.
If you have grassy slopes to mow that have a pretty steep gradient, it’s possible that while you’re mowing, the angle the mower is positioned at can cause oil to move out of the crankcase (by our good friend “gravity” again) and start to make its journey toward the air filter.
You Put Too Much Oil in Your Mower
Most residential mowers don’t require huge quantities of oil. The crankcases are generally pretty small. But if you overfill it way past the recommended level, the chances of oil spilling out of the crankcase are MUCH higher. Usually, this might result in some lawn mower oil in the cylinder, and you’ll see some black smoke (quite an alarming sight), but sometimes it might get as far as the carburetor and air filter (if you overfilled it to a stupid level).
So read up on how much oil your lawn mower takes, and whenever you’re adding oil to your mower, add very small amounts and use the dipstick to measure the current level. Keep adding small amounts until it’s within the range that is recommended by the manufacturer.
Internal Engine Problems
If you rule out the other causes I’ve mentioned, then this could potentially be the reason why your air filter is soaked with oil, particularly if your mower is quite old. A blown head gasket, damaged cylinder or worn cylinder rings are all potentials causes of oil traveling a path it should not and reaching the air filter.
If this is the case, unless you have considerable knowledge and experience with small engine repair, you’re going to need the help of a specialist to repair and reconstruct the engine. Depending on how much your mower is worth, it may actually be more financially viable to just buy a brand new mower, as engine repair can be expensive.
I Can See A Bit of Oil in My Filter: Should I be Worried?
Paper filters shouldn’t really ever have any oil on them. But if your mower has a foam air filter, you should be aware that a light coating of oil is completely normal. In fact, it’s necessary. It’s actually this oil that prevents dust and dirt from passing right through it.
It’s also fairly common that this type of air filter can get oilier over time, and that’s why you need to periodically remove and clean your air filter to restore it to its optimum condition.
All I’m saying here is, don’t freak out if you notice your foam air filter is slightly oily. It’s supposed to be.
Prevent a Lawn Mower Air Filter Soaked in Oil: A Few Final Tips
To wrap this post up, let’s very quickly summarize the main things you can do to prevent a lawn mower air filter from becoming soaked in oil.
- Don’t tip your mower the wrong way (#1 tip by far).
- Don’t put more oil into your mower than is recommended by the manufacturer.
- Be careful when storing your mower and make sure it’s completely level.
Observe these few simple but important rules, and you’re far less likely to experience this problem again.