Air Oil Separator vs. Catch Can: What You Need to Know

Most people think that catch cans and air oil separators serve the same purpose. As much as they both separate oil from the air that has its differences. It is crucial to know how air-oil separator vs. catch can differ from each other. The major difference is that the AOS separated air and oil and let the oil drip back to the oil pan while the catch can traps oil in a can.

This is because air oil separators have more baffles than the oil catch can. When using an oil catch can you will need to empty the captured oil regularly. In this article, we shall inform you more about Air Oil Separator (AOS) and catch can. This information will help you to make an informed decision when buying.

Air Oil Separator (AOS)

best air oil separator

An air-oil separator is a beneficial equipment since it works as a filter by separating oil going to the engine from compressed air. Oil is injected during compression to absorb, lubricate, and seal the heat of compression. Therefore, a mixture of oil and air is what comes out of the compressor element. The AOS separates air and oil since air is required to get out of the compressor while oil needs to stay in the compressor for lubrication.

AOS features more baffles that separate air from oil entirely and prevent oil from going to the air intake. This equipment makes it easier for you since oil will automatically go back to the engine, unlike when using an oil catch can. Some of the best air oil separators include Moroso 85481, Moroso 85474 Universal, and JLT Oil Separator.

Moroso 85481 is one of the high-quality air oil separators and is easy to install for GM trucks. These air oil separators do not require a lot of maintenance since they keep on dumping the oil they catch into the engine, and thus it cannot spill. Other air oil separators such as Moroso 85474 Universal air oil separators, have a large size, thus offering a higher capacity.

The AOS features separate inlet and outlet and filter screens on both sides. It has a 3/8 90 degrees inlet, and it’s polished with billet aluminum. Moroso is one of the best manufacturers of AOS, and they don’t disappoint. When looking for an AOS, consider its ease of service, such as Passage Side JLT oil separators. The AOS is made in the USA, and it uses plug-N-play installation, which is quite easy.

Read Also: Should I Check Oil Hot or Cold? How to Check Engine Oil

Air Oil Separator Maintenance

As we have said above, air oil separators do not need so much maintenance since they drain the clean and separated oil automatically to the engine. All that is needed from you is to install the AOS properly and leave it to perform its tasks. Go through the manual to see the right procedure for installing the AOS in your vehicle’s model.

AOS has a drain connecting to the oil pan, which enables all the oil caught to be used. This, therefore, keeps the oil circulating properly in the system instead of keeping it unused. However, it is advisable to wash the AOS after a while for durability, longevity, and engine health.

When cleaning the air-oil separator, remove it and start by flushing it with mineral spirits to get rid of oil. Use compressed air to remove mineral spirits and submerge the AOS in a carburetor and parts cleaner. It is advisable to leave the AOS in the cleaner overnight to get the best results.

Ensure that you have removed the air pockets on the internal surface of the AOS. After removing the AOS from the cleaner, rinse it using water and then use compressed air to remove any remaining water. Now you can install the clean AOS and ensure there is no oil leaking.

Oil Catch Can

A catch can is meant to catch excess oil passing through the piston seals and prevent it from getting in the air intake. This also prevents oil and other contaminants from building up in the air intake manifold. PCV Oil separator catch cans are placed between the crankcase and the PCV valve. Since the catch can collect excess oil, it needs to be rinsed and collected periodically.

There are several benefits you enjoy when using a catch can. Most of the best oil separator catch cans are made with aluminum. They are lightweight and quite durable. One of the best catch can with these features is Ruien 0046 oil catch can. This catch can be made with excellent performance and fashion appearance. It is universal, and it fits almost all types of carts.

Blowby reduces the engine’s performance and can lead to damage over time. Oil catch cans prevent oil and dirt from getting in the intake system and prolong the engine life and increase horsepower. An oil catch can, therefore, be an essential tool for most drivers with high-performance vehicles to get optimal performance from their vehicles.
One may wonder how I know that my Oil catch can need emptying. Most oil catch cans have a dipstick, which you can use to check if the can is almost full. You are encouraged to keep on checking the catch can occur once in a while to prevent it from overflowing.

When the oil fills up, it spills over, thus leading to more damage. Once the oil catch can is full, the oil starts to coat the air intake causing the engine to stumble. In most cases, oil catch cans are ideal for direct injection engines. Ensure you empty the catch can before it fills up with oil to avoid the repercussions.

Read Also: How to Dispose of Old Gasoline [Step by Step Guide]

Oil Catch Can Maintenance

An oil catch can also separate oil and crankcase fumes, but instead of returning the oil to the engine, it catches the oil. This, therefore, needs some little maintenance since you need to keep on emptying the Catch can. When using the cans, it is advisable to keep on checking on them so that the oil cannot overfill. You can use a dipstick to check the amount of oil in the can.

Draining the catch can is among its regular maintenance. How frequently you should empty the Catch can is dependent on various factors. Vehicles remove a different amount of contaminants depending on their models, age, types, and mileage. The driving style is also a factor that can affect the number of contaminants filtered. If you are a fast driver, it will yield more contaminants, and thus your Catch Can fill up more regularly.

To know the frequency, observe the oil catch can when it is new to see how frequently it fills up. This will guide you after how long the can needs emptying. In some cases, the Oil Catch Can will clog up, thus needing some maintenance. To remove the clog up, start the engine and open the drain valve. This will release the vacuum and get rid of the clog.

The other way to remove the clog is to take out the oil cap and open the drain valve. In case this method fails to use something like a paper clip to poke the drain valve. If the clogging is too much, you are required to remove the Catch can and run isopropyl rubbing alcohol for cleaning.

aos vs catch can wrx

What Is the Main Difference Between a Catch Can and Air Oil Separator?

Air Oil separators and Oil catch cans are made to capture oil vapors going through the PCV system and catch oil residue. The two devices work the same way but give different results.

An oil catch is put in an inline system for capturing blow-by. They have some filter or baffling-like features that help the oil droplets and oil vapor to fall out and air to pass through. Catch cans do not return oil in the crankcase. You, therefore, need monitoring to keep them from overflowing.

The cans are made with a large capacity to prevent them from being emptied frequently. Oil catch can sweat and build moisture during changes in a climate more than AOS. During cold days the sweat and water vapor from the engine condenses, filling the can with water.

An AOS is superior to a catch can. It is designed to take the collected oil back to the engine. With an AOS, you do not have to keep on emptying it. Condensation happens in AOS, but it is not allowed to get to large volumes. The little amount of water reverted in the motor burns off during usual operations.

Most high-quality Air Oil Separators have a high-quality built-in heater. It keeps the body hot, thus preventing condensation. The water collected evaporates and lets oil flow freely. This is what makes AOS better equipment in separating oil.

Read Also: 10 Best Gas Cans Review and Complete Guide

Frequently Asked Questions (FAQ)

Q. Do I Need Air Oil Separator?

Yes. An air-oil separator is an essential piece of equipment for your vehicle. An AOS separates air and oil and automatically sends the oil back to the engine. With an AOS, unlike using a catch can you do not have to keep on emptying it. The reason why you need an air-oil separator is to reduce the effect of blow-by. Blow by gasses causes builds up on the valves, thus reducing their performance. You, therefore, need an AOS to increase the performance of your engine.

Q. How Does An Air Oil Separator Work?

An AOS is connected to the PSV system between the vacuum source and the crankcase. The pressure from the crankcase goes via the air-oil separator, which has a series of steel mesh and baffles separating moisture and oil from the airflow. Some condensation happens in the AOS, but it does not pool. There may be a small amount of water sent back to the motor, but it burns off completely. Some air oil separators have inbuilt heaters, thus preventing condensation.

Q. How Do You Clean an Air Oil Separator?

It is advisable to clean the AOS once in a while. The right procedure to follow is as follows:

  • Remove the AOS according to the vehicle’s manual
  • Remove oil from the AOS by flushing it with mineral spirits
  • Get rid of the mineral spirits from the AOS using compressed air
  • Remove the air pockets from the internal surfaces by submerging the AOS in a carbonator and parts cleaner
  • Leave the air-oil separator to soak overnight
  • Remove the AOS from the carburetor and parts cleaner and rinse it using water
  • Get rid of any water from the AOS using compressed air
  • Reinstall the AOS
  • Ensure there are no oil leaks and it is operating quickly

Q. What Is the Purpose of Oil Separator?

Just like its name suggests, an air oil separator separates oil and air going into the engine. Once the AOS separates the hot gas oil, it returns the oil to the crankcase or in the oil reservoir. This device, therefore, prevents your vehicle from getting blow-by. When the two are not separated, they form a build-up in the system, which reduces your vehicle’s performance. Its purpose is to reduce the oil vapors recirculating in the engine.

Final Words

Oil catch can and air oil separators are necessary for vehicle owners who want to reduce blow-by and improve their car’s performance. With this information, you now know perfectly tell the difference between catch can vs. air oil separators. If you are using a turbocharged or direct injection engine, installing an oil catch can or air-oil separator will be beneficial for your vehicle’s engine. With oil catch cans, you will need to do oil changes more frequently. On the other hand, AOS does not need so much maintenance since it automatically separates air from the air and directs them to the engine.

Read More: 


Hi there, I am R. Hasan Tito, a mechanic, and owner of this website. My friend and I created this website to share our knowledge, expertise, and experience with our fellow mechanics' community and car users. I am a specialist and certified automotive mechanic (Both Heavy Commercial and Private Cars). I worked as a Mechanic and Mechanic Supervisor for over fifteen years at Global Rebound Automotive companies - Toyota, TATA, BMW, Nissan, TVs, and Others. Now, I enjoy my new role of leading a team of automotive experts (in their respective fields) and publish new content on a regular basis on my website and social media.

2 thoughts on “Air Oil Separator vs. Catch Can: What You Need to Know

Leave a Reply

Your email address will not be published. Required fields are marked *

Recent Posts