Oil On Your Lawn Mower Air Filter? [Top 5 Causes]

The most common reasons for oil on a lawn mower air filter are:

  1. There is too much oil in your mower engine’s crankcase.
  2. Your lawn mower was turned on its side with the air filter facing the ground.
  3. The mower was used to mow a slope and the air filter was on the downhill side.
  4. Your mower’s engine has suffered serious damage.
  5. Your mower has a foam air filter.

Paper air filters that have been damaged by oil must be discarded and replaced. However, foam air filters that have been soaked with engine oil can be cleaned and reused.

Oil on lawn mower air filter

5 Causes of Oil on Your Lawn Mower’s Air Filter

There are a few reasons your air filter might be soaked in oil. Below are the common causes of this problem, as well as how to avoid them.

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1. Overfilled Oil Reservoir

Too much oil in your mower’s crankcase can result in oil being pulled through the PCV valve and into your mower’s intake system. This will splatter your air filter with oil. To check if this is the problem, unscrew your oil reservoir cap and inspect the dipstick. If the oil level is past the upper fill line, the reservoir is overfilled.

Use this fluid extractor to remove excess oil until it is at the proper level. Just remember to wipe off the oil dipstick after each level check, to ensure an accurate reading.

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2. The Lawn Mower was Tipped Over

If you turned a lawn mower onto its side for maintenance or storage, the oil may have run out of the engine crankcase and soaked the air filter. This occurs when the air filter is facing the ground while the mower is on its side. If this happens, your mower may be low on oil. Check the oil level and top it up if necessary, since it’s a bad idea to run a mower without oil.

In the future, whenever you turn your mower on its side, make sure the air filter is pointing upward. This will prevent oil from soaking the filter.

3. You Mowed a Steep Slope

Similar to tipping your mower sideways, mowing across a steep incline can cause oil to run out of the engine crankcase and onto the air filter. This happens when the air filter is on the downhill side, because gravity will pull the oil toward the filter.

In order to stop this from happening, always position your mower so the air filter is on the uphill side when mowing across the face of a steep slope. Mowing the yard in a circular pattern makes this easier.

4. Engine Damage

If your mower has a blown head gasket or other severe engine damage, oil may leak onto the air filter. If none of the other causes on this list explain what caused the oil filter—or if you see oil on your new replacement filter—then your oil problem is probably a sign of even bigger engine trouble.

In this case, take your mower to a lawn mower repair shop to get a professional’s assistance.

5. Your Mower has a Foam Filter

Foam air filters used in lawn mowers are designed to be treated with a special oil to improve their performance. So, the oil may be there purposefully. However, it’s important to make sure this is the case. Foam air filter oil should have a slightly “tacky” feel when you press the filter. It is also very light amber in color.

If the oil feels slick or greasy, is dark amber or black, or smells strongly of engine oil, then you have an oil leak. Engine oil on a foam air filter is likely caused by one of the previous 4 issues on this list.

Do You Need to Replace an Air Filter that has Oil on It?

If your lawn mower has a paper filter, it must be replaced if it has oil on it. Paper filters cannot be cleaned or reused after oil has soaked into them. In this case, it’s best to throw away the oil-contaminated filter and replace it with a new filter designed for your mower. Read on to find out what to do about a foam filter with oil on it.

Can You Clean the Oil Out of a Lawn Mower Air Filter?

You can only clean the oil out of a foam air filter. Paper air filters with oil stains should be discarded and replaced. To clean a foam air filter:

  • Remove the filter from its housing.
  • Soak the filter in a mixture of warm water and dish soap.
  • Once the oil stains are gone, rinse the filter with clean water.
  • Allow the filter to dry.
  • Spray this foam filter oil onto the clean, dry filter.
  • Reinstall the filter in your lawn mower.

If you choose, you can also replace the foam air filter instead. However, a properly cleaned foam air filter has a long lifespan. So, cleaning it can save you money in replacement parts.

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Why is Your Lawn Mower’s Air Filter Covered in Oil?

A lawn mower air filter may become covered in oil if the oil reservoir has been filled too high. Oil may also contaminate the filter if the mower was tipped over on its side with the air filter facing the ground. Similarly, mowing across a steep slope with the air filter on the downhill side can cause oil to run out of the engine crankcase and onto the air filter. Less commonly, serious engine damage can cause oil to soak your mower’s air filter. Finally, foam air filters are treated with a special type of oil. However, this oil has a different consistency and smell than engine oil. So, check to see what type of oil has soaked your foam filter.

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