Oil catch can pros & cons

I`m not sure if there will ever be a good answer but maybe there is some technical document proof..
I know the catch can removes a lot of mess from the intake, but isnt the oil good for valves and pistons? After 15k kilometers with the catch can I think the valves god louder :/ And maybe there is some piston slap (haven`t sourced the problem yet). I`m just wondering and googling and never found an answer..
I`m really considering to ditch the can :roll:

this is from Corvette forum:

I have to agree here!!In fact I believe it is doing the Engine a Dis-Service!! In the old days of leaded fuel and No PCV system's, we were Lucky to get 50-60,000 miles out of valves and guides,And Really lucky to get 95-100,000 miles out of a set of rings!!!And then it was a sure bet that there were 2-3 cylinders tapered and you would have to bore it and get a set of pistons too!!Hardly any upper cylinder lubrication except a little lead, If you were a Car Buff,then you may put a few ounces of Marvel Mystery oil in every tank of gas for upper cylinder lubrication religiously and get 100,000 plus out of your valves and guides and maybe 150,000 out of your rings and pistons!!!My Grand Daddy and my Dad were Machinist and Fanatic's about upper cylinder lubrication, and I believe they were 100% Correct!! Heres Why!!I'm Old enough to remember when Cars didn't have a PVC system,just a Breather Cap and a 1 inch tube running from the back of the intake valley to just below the oil pan!! Since PVC systems have been used, engines have been lasting longer!!More Miles with less repairs!! Most all vehicles now days will get at least 100,000 plus out valves and guides some even as much as 200,000-300,000 miles!! My wifes 4.3 Jimmy has over 245,000 and has never had a head off of it, my daughters Z-71 had 196,000 on it and had a head gasket start seeping so we pulled the heads and I was amazed that I could still see the cross hatching in the cylinders!!!We put H/gaskets on it and it's hook'n down the road!! That wouldn't happen in the old days!!!

I'll have a few onces of Upper Cylinder Lubrication per oil change, Thank You!!

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I Agree, We used to use Marvel Mystery oil all the time, (40-50 years ago) in fact I still have some. They even used to make an injector plate that mounted between the Carb and intake manifold. Gave better gas mileage and a lot less upper cylinder wear,

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There is no actual data to indicate the catch cans either HELP OR HURT engine life or performance.
No company has any documented testing of validation of catch cans.

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While I don't see why this should be in the FAQ/Archive I will answer this.

Oil catch cans are air/fluid separators designed to remove the oil that is carried by blow by pressure into the positive crank case ventilation(PCV) system. If the oil is not removed it will travel back into the intake and leave deposits on the compressor wheel, throttle plate, and intake valves. Any oil that goes into the cylinder will burn and leave carbon deposits which can increased wear as well as promote detonation and preignition due to super heated carbon build up.

Possible causes of valve noise could more likely be due to poor regular maintenance or over revving causing damage to the lifter where it holds the shim. When I got my trac it had a valve noise on the number 1 intake but performed fine. Turned out the lifter's edge was broken and the shim would rattle a little in it's seat.

Some people have discussed the reuse ability of the oil that ends up in the catch can. Unless the oil is severely fouled(dark brown to black) or showing metallic particles, it is no worse then the oil that is in your pan. The only reason it ended up in the can was that it was pulled from the head by the intake vacuum that is normally employed by the PCV. If you have the can connected incorrectly you can severely decrease the life of your engine. Connecting it to either the intake between the compressor and throttle body or not connecting it to anything more then just the head will negate the purpose of a PCV system or in the case of being hooked to positive pressure actually aerate your oil and severely reduce the lubricating abilities.

Hope this helps. Regarding the corvette forums postings regarding older engines and marvel mystery oil; those engines designed to run on leaded gasoline used a softer valve and valve seat. The lead deposited from the gasoline would fill wear points and "lubricate" the system. Today's valve seats and valves are much harder and last much longer due to increased manufacturing tolerances. A leaded gasoline or upper cylinder lubricant does nothing for these parts and the lead will destroy your catalytic converter and 02 sensor FAST.

Lastly the argument that there is no documentation or proof is incorrect. All you need to see is a honda intake tube between the filter and the throttle body. Where the PCV system stems in there is a J shaped chamber on the opposite side of the tube. The oil picked up in the pcv system cannot make the hard turn from the PCV stem to the throttle body and so passes across the intake and collects in the J shaped chamber. On very high mileage hondas that have this you can slip that chamber off and drain out all the fluid and oil that has collected. A basic and effective factory catch can.

When i rebuilt my motor, i found a large amount of black sludge on my TVIS butterfly valves, and all the valve stems and heads were covered in carbon.

Im definately going to be adding a catch can asap.

If you have the can connected incorrectly you can severely decrease the life of your engine.

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I didn`t quite understand. The only way I see to connect the catch can is hose to PCV tube and one to air intake (between filter and turbo).

Connecting it to either the intake between the compressor and throttle body or not connecting it to anything more then just the head will negate the purpose of a PCV system

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"purpose of a PCV system" ? what is the purpose? i thought it`s for not putting that mess on the road..

or in the case of being hooked to positive pressure actually aerate your oil and severely reduce the lubricating abilities.

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What lubricating abilities? What does the PCV oil lubricate? and if you catch the oil in the can, it doesnt lubricate anything..


Thanks for sharing, you seem much more educated in this

BriinumsBo":1eztg7ic said:

If you have the can connected incorrectly you can severely decrease the life of your engine.

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I didn`t quite understand. The only way I see to connect the catch can is hose to PCV tube and one to air intake (between filter and turbo).

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Connected incorrectly would be as suggested in the third quote. More possible if one were to fabricate their own intake or intercooler setup.

BriinumsBo":1eztg7ic said:

Connecting it to either the intake between the compressor and throttle body or not connecting it to anything more then just the head will negate the purpose of a PCV system

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"purpose of a PCV system" ? what is the purpose? i thought it`s for not putting that mess on the road..

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Positive Crankcase Ventilation(PCV) systems are designed for the purpose of removing combustion gases, that push past your rings, from the crank case where if they are left there would foul your oil and increase sludging and decrease the effective life of the oil. Thus requiring a vacuum source to draw out those gases.

BriinumsBo":1eztg7ic said:

or in the case of being hooked to positive pressure actually aerate your oil and severely reduce the lubricating abilities.

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What lubricating abilities? What does the PCV oil lubricate? and if you catch the oil in the can, it doesnt lubricate anything..

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The oil that is being caught in the can is being carried by those exhaust gases being pulled from the crank case. It is the same oil as what is on your dipstick. You want that in your crankcase and not in your intake where as corey attested to it causes gunk and damage. That is the purpose of an oil catch can. Allow the PCV system to work properly without putting oil into the intake even under high boost conditions where the significant vacuum as well as high combustion pressures can cause a lot of gas flow through the crank case.

ironpanther":2pc00q9w said:

BriinumsBo":2pc00q9w said:

or in the case of being hooked to positive pressure actually aerate your oil and severely reduce the lubricating abilities.

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What lubricating abilities? What does the PCV oil lubricate? and if you catch the oil in the can, it doesnt lubricate anything..

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The oil that is being caught in the can is being carried by those exhaust gases being pulled from the crank case. It is the same oil as what is on your dipstick. You want that in your crankcase and not in your intake where as corey attested to it causes gunk and damage. That is the purpose of an oil catch can. Allow the PCV system to work properly without putting oil into the intake even under high boost conditions where the significant vacuum as well as high combustion pressures can cause a lot of gas flow through the crank case.

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i was asking about the lubricating abilities you meant. i`m not going to recycle the can oil anyway. if there is no can, the oil goes into intake and burns and leaves through the exhaust. either way it gets lost. so what lubricating abilities?

I talked to my dad, he also said, that no oil from intake is needed for the valves. as for the cylinder top rings, i dont know. it could create some deposits and the rings would shave off deposits instead of metal from cylinder walls :/

carbon is harder then iron or steel it would mar the rings not the other way around. The cross hatch and oil control ring are there to supply the correct amount of oil to lubricate the upper two rings. As long as the engine was built correctly and broken in properly it will properly oil the upper rings. If you are not going to recycle the oil that is fine but there were two ways you could reduce the life of the oil in your oil pan and those were to not connect the PCV to anything or connect it to positive pressure. If the crank case doesn't have vacuum it won't be able to pull those oil fowling exhaust gases as well. If it has air pressure coming in the PCV it will trap exhaust gases inside as well as just regular air and severely decrease the life of your oil.

to make it perfectly clear I am referencing the lubricating abilities of all the oil in the engine not just what is carried into the catch can.

The original purpose of the PCV system was to appease the envrio types. It's really an emissions control device(subsystem.) Its other merits are debatable.

My experience with a "catch can" (actually a fuel filter) in the PCV line was that over about a year it collected only about 1/4 teaspoon of gunk. It did nothing to reduce the amount of oil that accumulated in the intake elbow right before the turbo. It went in the trash and the PCV hose connected back to stock configuration.

Regarding the post from the Corvette forum, there are a lot of reasons engines last longer today than they did 50+ years ago, and I don't believe the PCV system plays a significant roll in it.

^I'm kinda leaning towards disconnecting my catch can also.

catch can is a waste of time, take that pcv tube and route that into the exhaust. You will get better draw from the exhaust and dont need to worry about the weight of the can, dumping it out, and and that garbage.

You will increase the performance of the engine doing it this way. where as you will not with the can.

that should fuel the fire.

how would you increase the performance? and wouldnt the exhaust provide pressure to the pcv line?
and i dont remember wether pcv or egr line, but it must be connected for a st185 to maintain idle :/

___Scott___":ffcz6m6x said:

The original purpose of the PCV system was to appease the envrio types. It's really an emissions control device(subsystem.) Its other merits are debatable.

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Correct. It's supposed to return the gases back into the intake tract where it can be burned.

The idea of a catch can is separate liquid oil from the gases to keep oil from coating everything in the intake tract. I had a Mercedes Turbo diesel with 200k on it. The intake plenum and valve stems were coated with thick, goopy oil. There was no PCV valve and the line went 10" from the valve cover to just before the turbo inlet! It sucked oil! I cleaned it all out and installed a high quality catch can. My engine remained clean thereafter. A high quality catch can will have baffles to aid in the separation process. A cheap POS can usually doesn't, and works poorly at separating.

The tighter the engine, the less blow by. If you vent to anywhere but the intake tract, a loose engine will have idle problems because you're releasing metered air. A tight engine will idle fine.

I have an extremely tight engine. I have a catch can system on my car and I've pulled less than a tablespoon of oil in 13K miles (over 6 years). The important thing is it's not in my intercooler.

So here's the bottom line. The PCV is an emissions control device. Period. A catch can installed in the system can cause no harm with some potential benefits. Buy a quality can, route the output back into the intake tract, live long and prosper.

ok, i connected the hose back. my friend and my dad convinced me that the oil is a massive detonation cause. though my DIY knock detection leds didnt show any "bad gas mode" for the 5 days without the can, but with the can i get it sometimes..

Oil is detonation friendly, however the amounts that you will get from you vent line wont cause a problem. If you're getting that much oil from your vent then you have bigger problems anyway.

I just wanted to point out that there is a differnce betweetn the typical pcv VALVE system you see on most cars and the pcv hose that is on ours.

the PCV valve is a emission device, however the pcv hose on our car is not.

the pcv as used on a race engine is to help the seal of the rings.

klue would you like to explain how the PCV system helps sealing of the rings?

since a race engine usually has a considerable amount of blow by building pressure in the crankcase, this must be overcome to produce power and conquer the pumping loss. when the engine is under high rpm conditions/load the port vacuum becomes high and can easily pull the excess pressure created by the blow by gas. this is turn reduces the pumping loss created by the pressurized block. -> this gives you the performance gain.

if you have the pcv connected in the exhaust with a properly designed stem to creat a vacuum you can get the same effect as running the pcv to the intake(except you dont have to deal with the residues)

my problem with the catch can is that they hamper the flow of the pcv.

as for the sealing of the rings-> it is my understanding that the vacuum that a good operating pcv system produces helps to oil control ring effectively under loaded conditions.

klue, you can definitely go into more details about each your sentence :smokes:
because for now the only bad point you mentioned is that catch can would be a restriction for the pcv air flow, not that the oil is needed or smth..

sorry im mildly retarded, so please excuse me.
do you not understand the above post, basically the more vacuum you can put on the pcv the better you engine will perform