Can I Use WD40 On My K&N Air Filter?

If you are currently using a performance air filter on your ride, then you probably know that it uses oil to trap dirt and you have to regularly re-oil it. If you don’t, read my other article where I talk more about performance air filters. What Does a Performance Air Filter Do?

The question this article wants to answer is, could you use WD40 to re-oil your K&N air filter? (or any other oil-based performance filters).

Quick answer – no, you should not use WD-40 to oil your air filter because they dry up too quickly and leave behind residue that could even block airflow. Always go for a proper air filter oil (squeeze bottle or spray). They cost about the same and they are designed for the job.

The quick answer aside, let’s now discuss in more detail about air filter oil, how they differ from WD40 and how you could take care of your air filters.

In case you didn’t know, the whole reason we use performance air filters is because they have much bigger openings – allowing more air to flow inside your car engine for extra horsepower.

But bigger openings also mean more dust, insects and air impurities entering our engine. 

Which is why performance air filters like K&N use oil to trap these unwanted impurities. Allowing their air filters to have high air flow but also keep the dirt out.

It’s important for these air filter oils to not dry up quickly – so they can still trap dirt even after thousands of miles or months of driving.

Without the oil in your K&N filters, dirt in the air is no longer trapped. Many nasty things will enter your engine through the intake – stuff like dust, debris, sand and even insects. 

For a short term, you won’t have any major damages. Probably just some internal scratches on your pistons or engine walls. Basically wear and tear damages – nothing to worry about.

Keep it up longer and these air impurities will accumulate in your engine – potentially causing engine failure that are expensive to fix. Especially if you have a turbocharged car.

Turbos increase car performance by sucking in surrounding air, compressing it and delivering it directly to the combustion chamber (immediately providing an extra boost of air for horsepower).

If accumulated dirt flows inside your turbo while it’s compressing air, it will be catastrophic. The turbo wheel fins might crack and these metal scraps will end up flowing around your engine causing even more damage. Not something you want.

Ideally, you should get the official K&N cleaning kit. Here are the steps:

1. Apply K&N cleaner onto the inside and outside of the air filter
2. Let it sit for 10 minutes
3. Gently rinse both sides with water. Use low pressure water
4. Let it naturally dry (must be 100% dried)
5. Re-oil using air filter oil. You could use spray or manually rub

Here’s an official YouTube video from K&N showing you hot to clean and re-oil your air filter.

The air filter oil is important. You shouldn’t use WD40, engine oil or any other for this. I will cover why in the later section. 

The K&N cleaner is not that important. If you don’t have this, you can just clean the air filter using soap and warm water. The whole point here is to remove dirt and degrease the air filter. 

Make sure you clean the inside and outside. And also be gentle – you don’t want to damage the air filter fabric. 

As I said, you shouldn’t do this because WD40 and air filter oil are made from very different components. They are meant to be used differently. 

Air filter oil is designed to penetrate the air filter fabric and stay suspended inside for a long period of time without drying up. This means air filter oil lasts a long time, will not add much restriction and work great for trapping fine dirt. 

WD40 is a lubricant with an anti corrosion agent – they will not penetrate air filter fabric. Instead, they will stay on top of the fabric and clog up the available air openings – making your air filter way more restrictive.

Also, WD40 dries up much quicker than an air filter oil. Which means after some time, you won’t have that oil on your air filter – allowing air impurities to enter freely. 

Long story short, applying WD40 will make your air filter extremely restrictive and then extremely nonrestrictive soon after – basically two of the things you don’t ever want from your air filter.

Using water and soap instead of the K&N cleaner is fine. The goal in this step is to get all the trapped dirt away from the air filter  – so it doesn’t really matter what solution you use.

Just make sure you clean the air filter gently. Don’t brush it too hard or use a high pressure water hose. This will damage the fabric. 

Don’t worry about cleaning the oil away. You are supposed to do that. Wash the air filter and let it completely dry. You will have to re-apply the oil again in the end anyway. 

Official K&N website mentions that you can go up to 50,000 miles before cleaning is required. I think that’s a stretch for marketing purposes. 

This really depends on your driving condition. I would recommend you clean it every 15,000 miles. Or shorter like 10,000 miles if you are often driving off road.

Honestly, you can decide this for yourself. After 10,000 miles, pop open the hood and check out how dirty your air filter is. Depending on that, you decide the interval.

Yes you can put too much oil and over saturate your air filter – ending up with a restricted air flow. Even worse, if you install an air filter that’s dripping with oil, it might even enter the engine (very rare though). 

If you are using K&N oil, you could track the saturation by looking at the filter color. Dried air filter is usually pale in color. Whereas K&N oil is red in color. 

Just make sure your air filter is consistently red throughout. Then you know that you have correctly applied the oil.

If you happen to accidentally apply too much oil, just let the air filter sit for some time and let the excess oil drip away. Once the dripping stops, you can safely install the air filter back to your car.