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Oil Catch Can FAQ

Posted by on 8/21/2018 to News
The Next Step of the Oil Catch Can and Why The GEN2 Oil Catch Can by McNally Is Different than Other Catch Cans?

The way an oil catch can works is very simple. Dirty air the is produced by GDI engines that will eventually coaked up the pistons and valves. This dirty air is cleaned to remove any contaminants and then returned back to the engine. What makes a better catch can is the effective filtering process and how much yield the Catch Can will produce. As one of the originators of a true PCV dual valve oil catch can McNally has taken the Oil Catch Can to the next level. The GEN2 Oil Catch Can by McNally has added an important design features that will produce a bigger yield of contaminants that will keep your engine clean and avoid coking issues related to GDI engines. As dirty air enters the can from the PCV valve it is pushed in with centrifugal force. This simple process pushes the contaminants of oil, water and carbon down and out as it enters the can. As the containments hit the cooler side walls of the can this will start the filtering process and keep the contaminants down into the can. Before exiting the can it will go thru another filtering process of coalescence. This new design concept will produce a larger yield of contaminants before entering the engine of the vehicle and extending the life of your engine.

How does a Catch Can Work?

In order for the pistons to be pushed down, a GDI uses gas that is injected to be ignited by the spark plug. The combustion forces the piston to go down. That combustion produces a gas that is a mixture of water, oil and carbon. This gas will sometimes escape past the piston seals down into the crankcase. This is called "blow-by" This will lead to an erosion of your engine's valves and will make the pistons work harder for them to go up and down. The positive crankcase ventilation system (PCV) works as air is piped to the crankcase via the engine’s existing air filter, run through the crankcase, and then through an oil/air separator (PCV valve) back into the engine’s air intake. This seems like everything would be fine except that dirty air is never really cleaned. More like re-circulated into the engine. So basically dirty air is constantly being added to the dirty air. This will lead to Coaked pistons and valves and to an expensive repair bill. So an Oil Catch Can's job is to take that dirty air and clean it before it returns back into the engine.

Do I need a Specific Catch Can for my engine?

The truth of the matter is the actual Catch Can is universal meaning it can go on any type of engine despite year, make and model. When a kit becomes vehicle specific it is because of the hose fittings. The hose fittings are generally called plug and play and will allow the installer to connect the hoses with no cutting involved. With these types of kits, the catch cans can only be placed where the manufacture of the kit tells you to. There is no deviation from their installation directions.

We here at McNally do not go with the Vehicle specific Oil Catch Can kit. We know that a cooler can will be more effective and placement of the catch can will be limited in some engine bays. We allow the flexibility of the installer to dictate where they place the can with enough hose length and connection types for all types of vehicles.

Can I install a Catch Can in the Cold Air Intake (CIA)?


Should I include the passenger side turbo in my Catch Can install?

There really is no need to do so. Keep it simple, neat and clean and only connect to the driver side turbo.

How do I install a catch can?

A catch can is a very simple process to understand. The sole function of an Oil Catch Can is to clean the Dirty air that can cause coaking within your engine valves and pistons. A Dual valve Oil Catch Can means there are 2 outgoing vacuum connections and one incoming connection. This incoming connection is the dirty air from the PCV line (positive crankcase valve) that is on all modern engines. The two outgoing ports will involve a one-way check valve, either in-line or built in. With the two outgoing ports, one line is to be placed before the throttle bottle and one behind the throttle body. Behind the throttle body is the idle vacuum. This is when the throttle blade is closed a vacuum is produced in the intake manifold. When you accelerate the throttle body blade opens up and the vacuum of air pressure is released from the intake manifold and goes to the air intake assembly. This is where you would place the second port line. As long as these rules are followed the exact placement of the lines really relies on the installer and the aesthetics they are looking for.

What is a Clean Side Separator and do I need one?

A Clean Side Separator is an add-on replacement for your stock Oil Fill Cap. Although approximately 90-95% of the oil ingestion via the intake air charge enters via the "Dirty" or "foul" side of the PCV system, the other 5-10% enter via backflow through the factory "clean" or "fresh" side tube. This occurs mainly when accelerating or at wide open throttle when intake manifold vacuum drops to zero and crankcase pressure is allowed to build. This pressure will seek the path of least resistance, which is back flowing into the intake air bridge assembly bringing in oil mist and other contaminants into the intake air charge.

A vehicle from the manufacturer is designed to have to correct amount of air in and out. When a vehicle owner modifies their engine a Clean Side separator will act like a breather. In a performance set up, a Clean Side separator will allow vapors to come in and out and not released into the atmosphere. The Clean-side separator solution addresses that small amount of oil vapor that enters the intake air charge upstream of the throttle body during wide open throttle operation when the intake manifold vacuum is not present. he Clean-side solution allows 100% MAF metered air entry while trapping the oil during wide open throttle operation and allowing it to return back into the valve cover as soon as the throttle is lifted.

How do I install a catch can if I have a turbo?

The installation of an Oil Catch Can in a turbocharged is really the same as a vehicle without turbo. The incoming port will always be the dirty air from the PCV (positive crankcase valve). You must connect one port line to the intake manifold and the other with the air intake assembly. With a turbo, the air intake assembly is connected to the turbo. The line can be connected anywhere in the air intake assembly but should be closer to the turbo but do not place the line any closer the 3 inches.

How do I install a Catch Can if I have a supercharger?

The installation of an Oil Catch Can in a supercharger is really the same as any naturally aspirated vehicle. The incoming port will always be the dirty air from the PCV (positive crankcase valve). You then connect one port line to the intake manifold and the other with the air intake assembly. A top mount supercharger or even a root style supercharge will typically have an auxiliary vacuum barb at the blower snout toward the front of the engine. You can connect directly to it and that is your second vacuum port line to feed clean air into the engine.

How do I clear a clog in my catch can?

There are cases when a catch can will clog up. Sometimes this just may be a vapor lock meaning the can has developed a vacuum that will not release. Start your engine and while it is idling open the drain valve. This should release the vacuum and clear the clog out for you. Another way to let air into your to unclog your catch can system is to remove the oil cap and open the drain valve. If this does not work try a paper clip or something of that nature and poke up into the drain valve. For the worse case situation remove the Oil Catch Can and run some isopropyl rubbing alcohol thru the can.

What is the difference between a single valve and a dual valve Catch Can?

The term single valve and a dual valve is referencing the outlet port on a catch can. With the single valve, oil catch can the in port connects to the PCV (positive crankcase valve) which is the outlet for all the dirty air caused by the blow-by product expelled by the engine. The out port connects to the intake manifold. You have to remember the intake manifold is before the throttle and the catch can only work when in idle. With a dual valve, the second out port connection goes after the throttle bottle. With a dual valve, oil catch can the can will work if the vehicle is in idle or in acceleration and is more efficient than a single valve oil catch can.

What if a catch can freezes?

The contaminant of what an oil catch can filters out is a mixture of water, oil and carbon. Even though Oil will freeze at a lower temperature there is still an amount of water that will freeze during cold winter months. This really will not pose a problem with your engine. The hoses of a catch can will never really freeze. When your vehicle runs at an optimal function the air that is circulated is very hot and any residue in your hoses will melt. If the contents in your can are frozen in the reservoir the can should still work properly. As long as the airflow runs thru the can it may eventually unfreeze what is in the content due to the hot air being rushed in. If you feel your can is totally frozen then the best thing to do take the can out and take it inside to let it unfreeze.

For environments that will have winter months in sub-zero climates, an oil catch can should be drained out. Some owners may prefer to take the actual can off for the winter.

How often do I drain my Oil Catch Can?

The general recommendation is with each oil change. The Truth of the matter is that every vehicle will produce a different amount of contaminants. You can have the same year make model and mileage of vehicles and will still have a different yield. There are many factors on how much contaminants are filtered out with an Oil Catch Can. One is the environment. Some of the mixture that is filtered is water. Dry arid climates vs humid climates will generally have a lower amount filtered. Another factor is driving style. If you are a bit of a lead foot then a higher yield of contaminants will be produced.

When you first install an oil catch can we recommend to check you can quite often. Get to know what your vehicle is doing and how it is reacting to a catch can. Do this for about a month then you will able to know when your catch can needs to be drained. Always drain your can when you have an oil change.

What do I do if nothing comes out when I drain my Oil Catch Can?

Sometimes an Oil Catch can system will create a vacuum that does not allow the can to drain. First, try removing the oil cap. This may allow the vacuum in the intake manifold to release. The best way to take care of this is to release the pressure by opening the drain valve while the engine is idling. This will allow the vapor lock to release and the contents of the can will drain.

Where should I mount my Oil Catch Can?

Most of the time an Oil Catch Can placement is where there is room in your engine bay. For the optimal results of a catch can it is best to have the can as far away from the heat of an engine. You will increase the yield of a catch can when the hot mixture is pushed thru a cooler can.

What makes a good catch can?

A good Oil Catch Can keeps what it catches. There are plenty of catch cans to choose from a vast price range. Just remember you generally get what you pay for. The $50 Catch Can you can get all day long on eBay. They basically consist of two ports, one in and one out, and the body is completely empty. You're basically paying for an empty can. A good catch can will have some type of filtering system design to catch all the bad contaminants from entering back into your engine. There are different types to filtering system as well. Some cans may only offer a screen filter while others offer coalescent filtration. A Coalescence filtration offers a larger filtration system for the contaminants to be filtered out on a molecular level thus collecting a larger yield from the filtration.

Will Installing an oil catch can void my warranty?

Yes and No. The truth of the matter it seems that each car dealership treats the installation of an oil catch can differently. There are dealerships out there that claim installation a catch can will void your warranty. On the other side, there are some dealership that recommends installing a catch can. So if you are purchasing a new vehicle I would ask the dealership about installing an oil can and what that means to your warranty.

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