Updated March 3, 2024

What Cause, How to Fix – Why Is There Oil In My Generator Air Filter?

Generators are powerful machines that are used to produce electricity when there is a power outage. They can also be used in remote locations where electricity is not readily available. However, like all machines, generators require regular maintenance to ensure their smooth functioning.

One important component of an open-frame generator that needs attention is the air filter. The air filter in a generator is responsible for the clean air that enters the generator’s engine through the carburetor. However, if you’ve noticed oil in your generator’s air filter, you might be wondering why it’s happening and what you should do about it.

But don’t worry, in this post, we will explain what causes, how to fix it, and what steps you can take to prevent it.

Why Is There Oil In My Generator Air Filter

The Function of an Air Filter in a Generator

Let’s first talk about what the air filter does in a generator before we get into why oil might leak from it.

The air filter in a generator works like a strainer, catching dirt, dust, and other yucky stuff from the air that goes into the engine.

It’s super important because it makes sure the engine gets clean air, which it needs to burn fuel properly. If the air filter gets dirty, the generator might not work as well, it could use more fuel, cause more pollution, and even get messed up in the long run.

So, Why is There Oil in My Generator Air Filter?

Oil in your generator’s air filter can indicate engine problems like worn-out parts or too much oil. This can harm the engine’s performance and cause damage if not fixed. It’s important to check and repair any leaks or engine issues that make this problem to keep your generator running well. Let’s take a closer look at each of them.

1. Overfill Oil Tank

One of the most common reasons is too much oil put in the oil tank. If you overfill the oil tank, the excess oil can find its way into the air filter.

This happens because the air filter is connected to the engine’s crankcase ventilation system. The crankcase ventilation system is responsible for allowing gases that build up in the engine to escape.

If there is too much oil in the crankcase, some of it can escape through the ventilation system and make its way into the air filter.

2. Worn Piston Rings

Another reason why oil might be present in your generator’s air filter is worn piston rings. The seals between the cylinder wall and the piston rings are created by the piston rings.

If the piston rings are worn, oil can seep past them and make its way into the combustion chamber. This can lead to a buildup of oil in the combustion chamber and ultimately result in oil finding its way into the air filter.

3. Clogged Breather Valve

The breather valve is responsible for allowing gases to escape from the engine. If the breather valve becomes clogged, gases can build up in the engine and force oil out through the ventilation system and into the air filter.

4. Faulty PCV Valve

The PCV (positive crankcase ventilation) valve is responsible for regulating the flow of gases in the crankcase ventilation system. If the PCV valve is faulty, it can cause too much pressure to build up in the crankcase, forcing oil out through the ventilation system and into the air filter.

What Should You Do If There Is Oil in Your Generator’s Air Filter?

Start by visually examining the engine of your generator. Look for any signs of oil leaks, such as wet spots or dripping oil, around the engine block, oil filter, or crankcase. Additionally, check for damaged gaskets or seals that could be allowing oil to escape into the air intake system.

1. Check the oil level

Verify that the oil level in the generator is within the recommended range specified in the owner’s manual, or repeat the oil change process.

If the oil level is too high, it can lead to excess oil entering the engine ventilation system and ultimately reaching the air filter. If the oil level is too low, it might indicate a leak or excessive oil consumption, which needs to be addressed.

2. Replace & Clean Air Filter

Remove the air filter housing or box and inspect the air filter. If you notice that the filter is saturated with oil or heavily clogged with debris, it’s crucial to replace or clean it. A clogged or oil-soaked air filter restricts airflow to the engine, affecting its performance.

3. Inspect Breather Valve & PCV Valve

After checking the oil level and replacing the air filter, inspect the breather valve and PCV valve to ensure they are functioning properly. If either valve is clogged or faulty, it will need to be replaced.

4. Check for Worn Piston Rings

If you’ve checked the oil level, replaced the air filter, and inspected the breather valve and PCV valve, and you’re still noticing oil in the air filter, it could be due to worn piston rings. You can check for worn piston rings by performing a compression test.

If the compression in one or more cylinders is low, it could be an indication of worn piston rings. In this case, you should take your generator to a professional mechanic for repair near your area.

Note: If you’re uncertain about diagnosing or fixing the problem yourself, it’s advisable to seek the expertise of a qualified mechanic or generator technician. They can perform a proper inspection of your generator, diagnose the root cause of the oil leakage, and perform any necessary repairs or adjustments.


Oil in your generator’s air filter can be a sign of various issues, such as overfilling the oil tank, worn piston rings, a clogged breather valve, or a faulty PCV valve. It’s important to address the issue promptly to prevent damage to your generator’s engine.

If your generator’s air filter is low in oil, it is not a problem. It is normal if you see that I changed or cleaned the air filter recently, and the next day it accumulates a lot of oil. This time you can take action on these steps, otherwise you don’t need to.


How Does Oil in the Air Filter Affect the Generator?

If there is too much oil in the air filter, it can restrict airflow, cause poor engine performance, increase emissions, and potentially cause damage if left unaddressed.

What Should I Do If Find Oil in Generator Air Filter?

Check for leaks, ensure proper oil levels, replace the air filter if necessary, and investigate underlying engine issues. Contact professional help if needed.

Can I Still Use Generator If There Is Oil in the Air Filter?

It’s not recommended as it may lead to reduced efficiency and potential engine damage. Address the issue promptly to maintain optimal performance.

How Can I Prevent Oil From Getting Into Generator Air Filter?

Regular maintenance, including checking for leaks, maintaining proper oil levels, and replacing air filters as needed, can help prevent oil contamination in the air filter.

About Saad Ahmed
Hi am Saad Ahmed and as you can see that i have been a generator mechanic for the past 12 years of experience in this industry. But now i am Full time digital marketer and affiliate blogger.