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3 Reasons Your Catch Can is Filling Up With Oil and Making Your Filter Oily

October 15, 2020 3 min read

Engine Catch Cans are a long debated topic.  After a ton of research, testing, and prototyping we have confidently figured out the do's and don'ts to Engine PCV (Positive Crankcase Ventilation) in order to keep oil in and get the positive air pressure out that is created by the movement of the engine internals and other factors. Follow these cause and solutions and you will be home free.

1. Lack of Baffling Where your engine vents from: Engines move a lot of oil.  Some areas move more oil than others. For instance, on an LS engine (both Gen 3 and Gen 4) the valley area are particularly high oil movement areas.  If you put a fitting here for PCV to a catch can you will surely fill up the catch can with a quickness, even with baffling its higher than most other locations.  Also right above a push rod hole on a rocker arm can get direct streams of oil which will fill up a catch can with unwanted oil if not properly baffled.  We try to avoid direct streams of oil with or without baffles.  We should note... You should NEVER need to put a sweatband or sock over a catch can filter.  That means your vent, or can baffling is inadequate.  These too get soaked and start to drip.  Very dangerous!

  • Solution 1: One being to take a piece of sheet metal strip and just slightly bridge it off the surface of whatever it is on.  You can do this in a vice or in a press break or box pan brake.  Either way welding or attaching this over the orifice of the fitting will make oil have to go around the sheet metal to get to the orifice rather than having a direct line of sight. 
  • Solution 2: We released this part last year with the sole intent of ending oil in catch cans.  These fittings bolt to the surface using three bolt holes with supplied hardware.  They seal with an oring to the surface.  They feature a dual baffling system (one external and one internal).  This means the air has to redirect several times to get into the fitting.  This baffling system allows the pressure to get out and the oil to stay in the engine.  We have torture tested this billet breather on the worst worn out engines as well as high horsepower race engines.  They work perfectly every time!  Available in 8AN, 10AN, and 12AN.

https://www.motionraceworks.com/collections/catch-can-pcv

 

2. No baffling in your catch can: When catch cans were first released as an alternative to running oil into exhaust or simply filtering it to the engine bay they were much different than how many manufacturers (including Motion Raceworks does it).  I will, however, note that many companies still have cans that simply have fittings in and a filter with little or no internal baffling.  When I mention baffling I am talking internal passages, or devices that redirect and block oil from having a direct path to the filter.  We have all seen those socks or sweatbands on catch cans, that is antiquated and no longer needed!  Check with the catch can you are using, if it doesn't have baffling, just say no!

3. Too Small of a system design: If you are running methanol and boost, it is very demanding on a PCV system.  In fact, many folks with these are creating so much internal crank case pressure that they do not even try to vent into a can.  They run a line from each valve cover into a large box in the back of the car.  The box does not have a filter, however, it has a "chimney" which evacuates the air directly upwards. This is why on high horsepower cars you will see the trunk lid "smoking".  That is the chimney.  Of course there is a large difference between a 400 hp gasoline N/A engine and a 4000 hp Methanol boosted engines.  If you have questions on line, can, and fitting sizes.  Feel free to reach out to our team.  sales@motionraceworks.com or call us (800) 878-9274 during business hours.  

There is one more reason why you are oiling up a catch can, but its more rare and we don't wish to scare you.  A broken ring land, piston, or other engine issues can create a ton of crank case pressure.  If your engine developed these issues out of nowhere, it may be worth doing a leakdown test to verify engine condition.  


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