OIL CATCH CANS

[john468]

I just bought a catch can and am very happy with the way it works so far.
But I would like to know how GM, Ford,etc,etc get awat with all this Bull?
Here we are spending a small fortune for a automobile that in my eyes is not working right from the start. I'm using and burning oil and getting the inside of my engine all gunked up with left over unburnt oil which in time its effects will become problems, unless I do something about it.( which I did ) All these companies that sell products (B&G, STP,Etc,) are making a fortune off this fixable problem. Why does the Goverment & EPA let them get away with it, do they own part of these companies or is someone getting a kick back down the line? Do you realize that if it starts to get bad enough and blows smoke you can get a ticket for the car builders PCV system. I don't know about you guys but the more I keep reading and looking at other cars this seems to be the everyday thing, having unburnt oil and using oil, not me. Take the test look in your intake passed the throttle blade and use a flashlight to really see what your looking for.
I'm sorry for raving on here but it just gets me why we all are helping others making money for a problem that should not be there in the first place. We are being ripped off here and saying nothing about it. What the heck, why not help out, buy that can of B&G Intake System Cleaners or one of there other products. Someone needs the money!!

[Mark H]

I'm interested on this also.
I have a catch can in my truck and it stops a lot of oil.

[joe h]

I've read the oil that gets through, lubes the top end slightly, reducing wear. But the internet is also an endless source of myths and brainless guesses.

[VTXrider]

Actually the EPA is the reason you have the PCV system the way you do. Back in the 70's the PCV would have drained through a small tube directly to the ground, if you are old enough you remember all roads especially highways had black strips down the center of the lanes. This was from the PCV drain. Then the epa decided that the most environmental solution was to have this oil burned through the engine instead of dropped on the ground. This is why the PCV gets feed back through the intake.

All cars have this issue however the larger and higher horsepower the engine the worse the oil blow by is. Also this issue is much worse on manual transmissions because of imperfect shifts that everyone does, I don't care about how good you think you are you do not always shift perfect. When the revs are not a perfect match the extra pressure pushes through more oil, again a 426 hp engine will push a lot more oil than a 250 hp engine.

[ITGuy11]

GM is fully aware of this problem and a fix is in the works - that is all I can say...

[SC2150]

Understanding PCV Systems

To understand why we need a proper PCV system one must understand what takes place in the crankcase during the average day of driving. First off, all internal combustion engines have a certain amount of "blow-by" or leakage past the piston rings into the crankcase. This consists of several compounds such as unburnt fuel and a small amount of the combustion gasses that result from the explosion of the air/fuel mixture. The combustion gasses contain several nasty things including sulfuric acid, carbon particles, and other caustic compounds that will contaminate the oil over time. In the crankcase there is also a certain amount of water, or moisture from condensation. Even if never run, an engine will accumulate moisture from the heat of the day to the coolness of the evening depending on how humid the climate is where the motor lives. Every time the motor gets run up to operating temperature these compounds are "gassed off" and with the OEM system it all gets "flushed" or pulled into the intake manifold where it is mixed with the intake air charge and burned in the combustion process and further in the catalytic converter before it is exhausted into the air as mostly just water vapor at that time. Now of course, a small amount keeps leaking past the rings into the crankcase and completes the cycle all over again, but without a proper vacuum pulled ventilation system....these nasty compounds will break down the oil and reduce its protection properties and the corrosive aspects start to rust internal parts resulting in reduced engine life.

In the "old days" of our grandfathers, the engineers that designed engines new the importance of evacuating these nasty compounds and the design was extremely simple. First was nothing more than plain breathers to allow excess crankcase pressure to be released or vented. But the damage from not "flushing" all the gasses out resulted in very short engine life (of course the oils of that day were nothing like the protection today's synthetics provide) so the next change added a vent tube, or evacuation tube that ran from the top of the crankcase to low on the car where the air streaming past would create a suction, or vacuum that would pull the vapors out and vent them directly into the air with a breather (barely filtered with a wire mesh type media that was oiled to catch dust & dirt) allowing the "fresh" makeup air in to complete the flushing process. Now this resulted in greatly increased engine life, but as the motors got worn oil would start to drip out the tube and drip onto the roadways, then the rain would wash it into the ditches, where it would enter the ground water (you know the rest of the EPA story) and the gasses just vented to the air.

As the EPA and the powers that be mandated stricter emission laws the system was refined more and more ultimately evolving into what we have today. A completely sealed system that uses the vacuum provided by the intake manifold to draw these vapors out, and the filtered fresh makeup air is drawn from the main air intake system and filtered by the main air filter. This results in very clean emissions, but the unintended issues are the detonation or "knock" that occurs when oil is introduced into the combustion chamber that the knock sensors pick up (before we can hear it) and pull timing to protect the engine from damage, and thus reduced power. Another result is the carbon buildup on the valves & piston tops (any techs reading this can surely verify the amount) also resulting in decreased performance and less power made.

The purpose of a proper oil separating catch can is to route these gasses through a baffle system that provides the most contact possible with the outer surface resulting in the oil being trapped and removed from the other gasses that do continue on through the intake and are burnt and consumed. It does NOTHING else in ANY way to the engine oil itself....it can't.

Deleting your PCV system:


While this will insure NO oil the the intake tract via the PCV, it will greatly shorten the life of your engine if street driven. The worst example I have seen is to cap off all the fittings and run an open hose from each valve cover to near the ground. One would think “they are both releasing pressure, so what can it hurt”. The answer is plenty. Lets take the basic principle of the Venturi effect. Whip a piece of hose around in a circle so that air rushes past the end. This will result in suction from the end of the hose near the center of the radius. Now with a car traveling down the road at speed, both hose will have air traveling past the ends and one ultimately will have more air rushing past thus creating more suction, and the other will them become a vacuum tube sucking up dust, dirt, water, sand, etc. directly into the engine from the side with the least suction. Depending on the amount of dust & dirt on the roads you travel (just look under your hood to see all the sand & dust that accumulates on the engine exterior). So it may take years to destroy your engine this way, or it may take no time at all. To see this if you have been misguided into doing this just remove each valve cover, and looking up into the baffle in each you will see the accumulated dirt built up as it comes in contact with the oil.


Now, addressing the "Home Depot" oil separator, it will and does catch a small amount of the oil but the majority still gets past into the intake (we used these and then the other cans that popped up on the market through the years before designing the ultimate final product that is offered today) and the reasons are simple:

It is plastic and transfers heat very inefficiently so very little condensing takes place.

The size. Anything less than 1 qt capacity and there is not enough surface area to be as functional, and the volume needs to be enough to allow the flow to slow enough for the oil to drop out of suspension.

And the lack of an effective baffle system allow oil to be pulled directly through.

As for having steel wool or another type of filter media inside, this will work well at first to trap oil....but as soon as it gets saturated droplets are pulled off and into the intake.

Why don't the auto manufacturers incorporate something similar? Cost and the added maintenance was deemed something that would NOT be accepted by the general market. (even though it is as simple as draining the can at each oil change).

Bottom line is this: The OEM system does a great job of meeting emission standards and removing the harmful contaminants, but the unintended consequences are the oil that is drawn into the intake charge. For an engine to produce the maximum amount of energy per explosion (of the A/F in the combustion chamber) you want air & fuel only....any amount of oil in this mix will hamper the explosion resulting in less energy released, detonation, and carbon buildup. Trapping and removing this oil before it gets into the combustion chamber is the ONLY solution to maintaining the maximum efficiency and prevent excess carbon buildup.

Understanding the need for
a proper PCV oil separating catchcan

Any engine driven hard will ingest a certain amount of oil into the intake air system resulting in loss of power, detonation, and long term carbon buildup on the pistons & valves reducing the velocity and flow through the engine.


Preventing this on a street driven car subject to emissions requires some simple modifications to the closed OEM PCV system.


On all out race applications where emission rules do not apply, this is accomplished in different ways, but proper crankcase ventilation is a must! The crankcase gets filled with harmful combustion byproducts that if not evacuated will cause internal damage to your engine and shorten the usable life. These byproducts include: Sulfuric acids, abrasive carbon particles, unburnt fuel, water, and more. If you do not have a proper crankcase evacuation system these compounds will condense inside the engine and mix with the oil as well as begin corroding internal parts. It is NOT enough to just vent the crankcase pressure through a breather, but it must be flushed with a filtered fresh air source to carry these out & away. In an OEM system, these are burnt in the combustion chamber & further in the catalytic converters.


In an off-road or race application, the engine is normally not used to burn them off.
At the very least drag only motors have a scavenge evac system in the header collectors to pull vac, and anyone that's serious has a belt driven vac pump.....especially the Alky motors due to the amount of moisture the alcohol introduces to the crankcase. Next time your at a sanctioned (NHRA/IHRA) race walk around the pits and look at the dragster motors and how they evac. You will see that any w/a vac pump run a relief valve on the opposite valve cover because if you pull any more than 14-15" of vac you start to pull oil off the wrist pins & rod journals.

I have run a pro team for 7 years and we run most every sanctioned track in the Eastern US and have yet to see a high HP dragster or door car w/out evac.

Want to see whats in your oil? A simple oil analysis will show you how much harmful stuff ends up in it.


The oil analysis will show the acid build up....and no, it takes a year or two before you would see any substantial damage to your internal engine parts.....but an easy way is after 6 months or so of running like you describe pull a valve cover and look and the corrosion from the vapors on your rocker arms. This is the first place it is visible.

More of my background? My team holds several local, divisional, National, & World championships in Super Pro, Super Comp, Quick rod, Top Dragster, and non-electronics.....I am also a graduate of the Reher Morrison Racing engine building school and have been an engine builder for over 35 years as well as having an engineering & machinist background. Take a little time & read David Reher's tech tips......a world of information: http://www.rehermorrison.com/blog/?cat=3

Bottom line is, w/out a proper evac system you WILL sustain long term engine damage. It may take a few years to notice, but I build motors 6 days a week when not racing and see the results first hand.

There are several other ways for oil mist to enter the intake manifold, the PCV system is the most common with the fresh air make up source (the fitting on the top rear of your throttle body) being the second most common. To eliminate that you need to cap the TB fitting and run a valve cover breather (installed as far from the crankcase vent as possible...ideally you want to pull filtered fresh air in one valve cover & evac it out the other or the LS6/LS2 style valley cover is second best) Then if it is excess crankcase pressure pushing oil vapor/mist out faster than the PCV can evac it you will see it pushed back through the line from the pass valve cover front to the TB and it is ingested from there. The 3rd point of ingestion is from reversion. This of course needs at least one piston/ring/bore/valveguide or seal issue that is allowing oil to be pulled into that one or more intake port and at high RPM's the reversion pulse will "push" that oil throughout the entire intake manifold. It will appear to have entered from the vac fitting that the PCV system uses but is really from one of the cylinders (reversion is a whole different process that is not widely understood but do a Google search and you can actually find some super high speed video of engines on dyno's where at high RPM's...9-10-12K plus the reversion cloud of A/F mixture is actually rising out of the intake runners or carb on a non fuel injected motor). To test for that just place a clean clear fuel filter inline between the catch can outlet and the vac fitting. If it gets oil on the can side, oil is coming through the can. If it first appears on the intake vacuum side, then it is reversion so you have a deeper issue.

Having engine smoke or excess crankcase pressure? There may be a deeper issue. On the LS motors we pull apart it is usually # 7 ringland broken between the compression & middle ring, or the land itself broke off at the top. We also find the top ringland pinched or crushed down on the top ring (comp. ring) and metal transfer along the piston side has caused the oil & scraper ring to stick allowing oil & blow-by. Also, try this: at idle (vac is at it's greatest when at idle or when the throttle blade closes from high RPM's) remove the oil fill cap and hold your hand over it. Does it pull a slight suction? If so, all is good with most of the system and I doubt you have a damaged piston/ring/bore. But if there is ANY pressure pushing back you have a deeper issue and that is the cause of the oil problem.

Now on big cam/stroker builds a can inline on the dirty side, and a can inline from the fresh air source may be needed (the bigger the bore & longer the stroke, the more crankcase pressure is built up) If it is forced induction, then you have a whole new process to deal with......and that is the PCV system works properly when at idle & non-boost, but when you start making boost you have switched from the intake manifold being negative atmosphere to a pressurized component and the PCV system is rendered useless and pressure escapes wherever it can. The solution then is to have one way check valves inline so the vacuum need for proper evacuation comes from in front of the compressor (head unit) through a line run to the air filter.

This is getting a bit long and I hope all can follow this, but if not ask me specific questions for clarification so this helps all. I'll go over every type of solution and the pros & cons of each....and remember, this problem is NOT just in the GM LS based engines, but is an issue with ALL modern closed systems. We just tear into our cars where as the Mercedes or Lincoln owner never even realizes there is an issue.

I also wanted to address the water in the oil. You will NOT fill your crankcase up in short order with just breathers. What happens is each time your engine reaches operating temp the unburnt fuel, water vapor, combustion by-products will gas or "flash-off" as vapor. But only the excess crankcase pressure being relieved through the breather will carry any of that out....and without a proper evac system, a good amount remains in the crankcase and re-condenses back to droplets that coat the internal engine parts as your motor cools down and it contaminates the oil. Every time you heat cycle you are adding more contamination and it is not very visible to just "look" at your oil....you need a professional analysis to see just what is accumulating in your oil and how it is breaking down its ability to protect...but the corrosion from the sulfuric acid is also very damaging over time (I'll try to post up some pics of parts showing just this in the near future). Just pull the dipstick on a diesel 20 miles after an oil change...it already "looks" black & dirty, but is still new and providing the proper protection. Sight is deceiving. Oil might look pretty clean or dirty but an analysis report will show destructive levels of contaminants.


And finally, some have gone so far as to cap off the entire system and run an open hose from each valve cover to near the ground. While this will eliminate all oil getting into the intake via the PCV system, the damage done by the hose with the least amount of air moving past it while at speed will suck dirt/sand/dust/water/and who knows what else directly into the motor via that valve cover. It may take some time (depending on how clean the roads you drive on are) but will result in premature engine wear & failure.


The solution for the street crowd is a properly designed, good functioning oil separating catchcan. Many are available on the market, but ONLY one designed with internal baffling and a good distance separating the inlet from the outlet. Many of the cans seen for low prices on Ebay, etc. are great looking, but are nothing but empty cans with two fittings attached. Do your homework & get a full understanding before you make your selection.