Ditch That PCV System Before It Is Too Late

"themushman" (themushman) 09/12/2014 at 16:27 • Filed to: None

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Yes, PCV, not PVC. Positive Crankcase Ventilation. Does your car have this “system”? Yes, more than likely; unless you are Orlove and drive an antique. Let me clarify something here. Positive crankcase ventilation is a requirement for almost every gas powered combustion engine found in cars. But how its utilized in modern days is what could be harming your engine.

In case you are unaware, when an engine is running and the piston is forced downward from the combustion process an unavoidable amount of air/fuel/gases makes it past the piston rings which “seal” the cylinder chamber. This mix of air/fuel/gases is a result of the pressure created from the combustion/explosion. It gets forced into the crankcase. This is called blow-by. To combat this pressure inside the crankcase, they developed a vent for it to vent out the pressure or keep a even pressure inside the crankcase.

With me so far? Great! So this is all fine and dandy, really. Except one thing. Inside the crankcase lives lots and lots of motor oil. So, all of this blow-by forced into the crankcase gets vented and along with it comes oil. In the early days, they used what was called a draft tube. Basically it was a tube that attached to the motor where this vent was, and it ran down to the bottom of the engine bay under the car. The draft of air under the car while you were driving whisked away the oil from the tube and straight under the car on to the road.

Eventually we figured out that this all was not the most environmentally friendly or efficient way to go about dealing with blow-by gases. So “we” developed a new way to process this pressure and escaped oil. And what ingenious technological advancement was that? Feed it right back into the motor!

Alright, that sort of makes sense. Keep the gases and oil inside the motor where they belong. Well, once you realize WHERE it feeds back in is where it starts to make less sense. It just so happens that that majority of the time this goes directly into your intake track, intake manifold, or throttle body. Often one side of the system is connected via a small hose to the air intake tube which helps put the system into a vacuum. The other side of the system has a one-way valve which lets pressure escape where it is then fed into your intake.

Whats the problem with that you might ask? Well, you are blowing motor oil into your intake system. Simple as that. Depending on your car and where it feeds back in, it can gunk up your throttle body, your intake tube and resonator, your entire intake manifold, etc. And no matter what, it makes its way back into your cylinder. And oil INSIDE the cylinder is bad. It gets burnt in the combustion process. That itself is not really a big deal. Burning a little oil, therefor losing a little oil. If it was vented to the atmosphere like in the old days, you were still losing oil. But the problem is on modern fuel injected and computer controlled motors that it can really ruin the performance of your motor. Oil being burnt in the combustion process can cause detonation, which is bad. It can cause knock which is bad. If you get detonation you can physically harm your motor. If you get knock, your car will pull fuel and timing which means you have less power and performance and lessen MPG. It will also start to ruin things like your throttle body and cause it to not function properly because its all gummed up with sticky nasty oil and sludge.

So, how can you do something about this? If you have not heard before, there is a item called a catch can. Its pretty simple really. And lots of people use them on performance builds. However, I am in favor of any enthusiast using them no matter how much or little horsepower your car has and regardless if you race or track your car. A catch can is simple really. It is a..well...can. There are hundreds of variations from generic-fits-all to vehicle specific. But they all work on the same principal. It gets inserted between the outlet of the PCV valve where the pressure (and unwanted oil) exits the motor. One side is connected to the PCV outlet, and the other side feeds in to your intake track. So, you are literally just inserting a component in the middle of the system that already exists.

How does it work: A good catch can has a “media” of some sort in the top portion of the can. It works similar to how a catalytic converter works. It creates surface area for oil and gunk to stick to, the air passed by and goes out the other side of the can, and the unwanted oil drops to the bottom of the can. It is basically a “Trap” for that unwanted oil. You empty the can regularly (I do mine at oil change, and once in between) to keep it from over filling. If it overfills, you are defeating the purpose and just blowing oil into your cylinders again. Its pretty much maintenance free and easy to “use” and install.

So, do your engine a favor and purchase or make a catch can. After your car burns up what oil is in the system from years of neglect it will thank you. You might see better performance and at minimal, you will be protecting your engine from the harmful effects of positive crankcase ventilation recirculation. After you drive it around a few thousand miles and see just how much oil it collects, you will be shocked. And typically, the older or more mileages you have, the more worn your rings are, and the more oil you likely have poisoning your motor. It is a cheap and easy mod to be sure no unwanted oil gets in your cylinders. Look through your throttle body, is there oil pooled up in the intake manifold? You could benefit from a catch can.

Lastly, if you want to ditch the chance of oil getting back into your motor via the PCV system altogether; its also pretty simple. Get a catch can, and instead of routing that outlet hose of the catch can back into your intake track simply put one of those little breather filters on it. This allows the air pressure to escape as intended, but still collects and keeps the oil in the can. In the even that it does make it past the catch can, it will just make a little smudge on the underside of your hood you can wipe off easily (although that likely wont happen). You are keeping the ground and your car free of unwanted oil and everyone is happy.

Adding this after the fact. I just went and emptied mine, if you care to see. This is after about 3000 miles

Old posting, but just found this video where the chief engineer for the hellcat engine discussed the need to have oil removed from the intake air so it doesnt cause issues like knock :Skip to 14:20

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crowmolly > themushman 09/12/2014 at 16:33

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Great article but the title is misleading. You are saying to modify your existing system, not delete PCV entirely.

Also, depending on where the valve is it can suck up oil during hard acceleration or braking.

XJDano > themushman 09/12/2014 at 16:34

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yeah I need to do this. 255K and oil constantly on air filter.

themushman > crowmolly 09/12/2014 at 16:35

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Crap, my last paragraph got cutoff when i copied and pasted it. Ill fix it (its the part about ditching altogether)

deekster_caddy > themushman 09/12/2014 at 16:36

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I like your idea of a catch can, but the amount of oil in the blowby is very very small, and shouldn't be a major factor on any street driven well maintained vehicle.

PCV inlets are usually directly in the intake manifold, AFTER the throttle body, so they shouldn't be making a mess of that. Plus, the source (PCV valve) is usually placed in a very high location so gravity helps keep the amount of oil to a minimum. It's a very fine vaporized oil that's actually making it into the airstream, which is really harmless. I've disassembled high milage engines that did burn a fair amount of oil and never seen any negative effects of it. (Maybe the nitrous shots burned the oil off the pistons...)

Overall good advice, but I would really only be concerned on a racing engine.

Twingo Tamer - About to descend into project car hell. > themushman 09/12/2014 at 16:37

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My car vents into the intake in front of the turbo, every 4th or 5th start it makes a worrying puff of blue smoke due to it burning off the little bit of oil. Oil level hasnt dropped at all and the blue smoke is only on start up so I assume that's what it is.

Frank Grimes > themushman 09/12/2014 at 16:38

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I would like to see someone test this on a dyno. Run two engines one with catch can and one without and see the results.

JGrabowMSt > Frank Grimes 09/12/2014 at 16:40

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There's no power increase. Don't be fooled by that. A catch can is ONLY to keep the intake clean. There is no power benefits to it whatsoever. If the dyno run changes noticeably with or without a catch can, you need to thoroughly check everything, because it shouldn't.

themushman > deekster_caddy 09/12/2014 at 16:40

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I dont race my car, but fill up 1/4 to 1/2 of a catch can every 5 thousand miles.

RamblinRover Luxury-Yacht > crowmolly 09/12/2014 at 16:41

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I was going to play devil's advocate and say a catch can is exactly like a ditch for engine runoff, so it *is* ditching. Of course, by copping to the missing paragraph, he spoiled my fun.

Will with a W8 races an E30 > crowmolly 09/12/2014 at 16:41

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Some VWs (B5 platform, probably others) use a nifty little swirl canister to separate air from the oil, similar to the vortex tubes in a Dyson vacuum. This helps them do a rather good job of keeping oil consumption down. Less nifty, however, is that in freezing temps with lots of short trips, they tend to ice over from the condensation. This then plugs the crankcase ventilation system, leading to the crankcase ventilating itself either through the valve cover gaskets or via an oil geyser out the dip stick tube and into the Taco Bell parking lot.

JGrabowMSt > themushman 09/12/2014 at 16:42

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I think the most important thing you need to do is touch on the correct type of hose for the job.

Because it's a vacuum, using the wrong hose will result in a problem. It's very important to get the correct hose, and make sure it is working correctly both at idle, and after a long run in case the hoses collapse under heat and pressure.

themushman > Frank Grimes 09/12/2014 at 16:42

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Im not sure it can be measured in that way. It is more of a solution to miles and miles and years worth of oil making it back into your cylinders. Unless you rings are really worn out, in which case the loss of compression is probably hurting worse than some blow by oil

HammerheadFistpunch > themushman 09/12/2014 at 16:43

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The other name for this article could be P0401. Land cruiser owners are familiar with it. I just had my entire intake tract cleaned with the head job...it shouldn't be a problem for another 250,000 miles or so.

themushman > JGrabowMSt 09/12/2014 at 16:43

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You can usually use heater hose. It holds up to both the vac and the heat.

themushman > deekster_caddy 09/12/2014 at 16:46

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I should also note my car is low mileage. Ive used them on several cars now and the amount of oil it will collect obviously various from motor to motor and how its driven, mileage, etc. But I have always collected enough to be grateful I spent $50 and 30 minutes putting one on. Will your car blow up if you dont? No. But I think its a good cautionary measure most car enthusiast here would be interested in trying to prevent unnecessary build up in their engines. General public and John Doe Camry driver? Probably not.

deekster_caddy > themushman 09/12/2014 at 16:49

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The question is how to get one in between the turbocharger and intake manifold. Because I know thats a place oil gets in our VW, due to the pure filth built up in it's intake manifold. Should put a huge intercooler in with a drain plug at the bottom!

RallyWrench > themushman 09/12/2014 at 16:52

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Good explanation, but it needs an amendment. Catch cans are great in some applications, particularly if boost is involved, but this shouldn't be done on anything OBDII, 1996 or newer. Most modern PCV systems are integrated into the valve covers or intake system in such a way that bypassing them is functionally impossible without major modification, and the ECM's air flow calculations are based on the assumption that the PCV system is recirculating properly with a known amount of vacuum. Also, if you have to pass emissions inspection, you won't because no legitimate smog tech will pass a catch can on anything that's supposed to have PCV. If it's an older car or you don't have to pass emissions, knock yourself out. Just don't forget to drain it periodically or it'll make a hell of a mess!

A big problem with late model direct-injected cars is carbon buildup in the intake ports due to the PCV system, because there's no longer any injector there to keep the back of the valve clean. So in severe cases, we have to take off the intake manifold & clean them with walnut shell media. Throttle body cleaning is generally pretty easy by comparison.

deekster_caddy > themushman 09/12/2014 at 16:52

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I had a 300,000+ mile VW Rabbit Diesel years ago that had so much blowby it would literally pool up oil in the intake manifold, and every now and then that puddle would overflow and feed the engine like fuel, at which time you were off to the races whether you wanted to or not! I used a 1 gallon windshield washer jug and some heater hose off the PCV system to build a 1 gallon catch can. I had to empty it every week or we were going for a random wild ride. I never had to change the oil because I needed to add a quart every time I filled up with gas... in addition to pouring the catch-can back into the crankcase!

themushman > JGrabowMSt 09/12/2014 at 16:52

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It wont give you any more power. But if you have a significant amount of oil being burnt in your cylinder, you will get some amount of "knock retard" which on most cars pulls timing and lessens the power produced. So if its significantly bad, a catch can would only help restore it to ideal conditions. Like I mentioned, its not something that will be noticeable on a dyno unless its a very severe amount of oil..in which case, you have other things to worry about. I monitor knock retard on my car everytime i drive it. When i see knock, first thing I do is check to make sure the catch can isnt full.

RallyWrench > themushman 09/12/2014 at 16:55

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Short term, but if it's not petroleum rated it won't hold up to oil for long.

themushman > RallyWrench 09/12/2014 at 16:55

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well if you are coming PCV valve -> can inlet->can outlet -> intake manifold, vac shouldnt be affected at all.

jariten1781 > deekster_caddy 09/12/2014 at 17:04

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Direct Injected turbo engines are totally fouling up the intake valves due to increased blow-by from the turbos and no longer having the cleansing action from fuel on the backsides of the valves. Catch cans have been a decent mitigator of that phenomenon on a lot of regularly driven non-race cars.

themushman > RallyWrench 09/12/2014 at 17:07

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Ideally you hardline it. But thats not easy for most people. But if you go to the autoparts store ask for the correct size hose for your application (probably 3/8 or 1/2"). Any hose Ive ever used is ok with oil..but good point to mention

mcseanerson > themushman 09/12/2014 at 17:08

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Quick question: Not to argue with you but if catch cans are so great why don't manufacturers install them?

themushman > deekster_caddy 09/12/2014 at 17:09

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rofl. Thats possibly the most extreme case ive ever heard. Thats awesome. A few years ago i bought a brand new challenger. After about 6K miles it already had oil pooled in the intake manifold. Its always worth a look in my opinion

themushman > mcseanerson 09/12/2014 at 17:12

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the average joe blow isnt going to care or notice the effects of PCV oil. People on this site, that care about their car and how it performs would. Plus its just another maintenance procedure that the end user would have to do which could be a turn off to a buyer. Plus..like someone else mentioned, it may be an issue with emissions as well

crowmolly > RamblinRover Luxury-Yacht 09/12/2014 at 17:19

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The ones I've seen and installed have been used in tandem with PCV systems. To have the oil drop down into the can only allowing clean air through.

With a setup like this, wouldn't you run into issues as a PCV valve operates on vacuum and this doesn't? At high RPM and low vacuum the PCV closes. This would stay open. Not to mention that increased air is now being added to the engine so you may need a tune.

crowmolly > deekster_caddy 09/12/2014 at 17:20

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Probably just run a pan evac or something then anyway, right?

6cyl > themushman 09/12/2014 at 17:52

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I agree a catch can is a good idea but IIRC if you vent the catch can instead of re-routing it back into the intake you can mess up the calibration of the MAF/AFM.

themushman > 6cyl 09/12/2014 at 17:56

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You may be correct with a MAF system. I know on a MAP system, as long as you cap off the fitting where it went back into the intake manifold, all is well with the world. MAF might be a little more sensitive to it. Good point

TwoFortified > JGrabowMSt 09/12/2014 at 18:03

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This is not strictly true. While I agree with you that hoping to see any measurable increase on two back-to-back dyno runs is a bit unrealistic, Oil mixed into the combustion charge lowers the effective octane (causing knock sometimes), and is therefore a loss in power.

RallyWrench > themushman 09/12/2014 at 18:13

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Yep. I've used heater hose temporarily too, but it turns to mush in pretty short order sometimes.

BJ > themushman 09/12/2014 at 18:45

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What effect can atmospheric conditions have? I've heard that in humid locations and/or cool weather you'll end up with water and oil in the can and that it can fill up quickly, as in you need to empty the can weekly.

Little Black Coupe Turned Silver > RallyWrench 09/12/2014 at 18:58

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Look up the problems the Cobalt SS Turbos were having due to the carbon buildup. A company has put together a "PVC upgrade" with a catch can that self-drains back into the oil pan. It's pretty much eliminated the need for the walnut blasting.

Nick, Drives a Cobalt LT > themushman 09/12/2014 at 19:01

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Some cars actually need that blow by.....My turbo loves the extra oil it gets in from the intake, actually helps to cool things down.

signintoburnerlol > themushman 09/12/2014 at 19:16

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Already have a catch can on the FRS...

Shifty > themushman 09/12/2014 at 19:57

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I run an Elite Engineering model on my Corvette (low mileage), and I fill it at about that same rate. Great investment!

Biapilotaceman > themushman 09/12/2014 at 21:12

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I may be wrong, and I'm really just asking to see if you know, but isn't this the purpose of the air oil separator on a water-cooled porsche? at least that's what the name leads me to believe.

Reborn Pyrrhic > mcseanerson 09/13/2014 at 10:45

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Peugeot and Citroën did!

The XU family of engines comes with a built in catch can, which gets the PCV pipes through it, and contains a media on the lid. The outlet feeds into the intake below the throttle body. The trapped oil falls to the bottom of the can, and is drained into the engine sump.

V8Demon - Prefers Autos for drag racing. Fite me! > themushman 09/13/2014 at 11:47

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Of the 4 cars I own, only one could really benefit from this. That would be the Dodge. Damn thing swallows way too much oil for a vehicle with 60K on the clock. I should not lose a quart between changes on a car made in 2008..... Unacceptable in this day and age.

Texican > 6cyl 09/13/2014 at 12:56

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If the catch can is properly sealed, and the outlet goes back to the intake where it originally was, it's sum zero. The MAF is already calculated with the "leak." Old Redblock Volvos use a MAF, and catch cans are common mods due to the weakness of the original system. It likes to plug up, making the crankcase pressure blow the main seals.

llamaguy > deekster_caddy 09/13/2014 at 13:59

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Exactly. I think a lot of people mix PCV with EGR as terrible, performance killing emissions equipment. EGR can cake up and choke an intake like it's going out of style.

Jaxinc > deekster_caddy 09/13/2014 at 16:46

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I have a half quart every oil change that blows out, typically out the exhaust as flames after it gets sucked back into the motor.

deekster_caddy > llamaguy 09/13/2014 at 16:55

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EGR can also be replaced with variable cam timing - just move it far enough to create Atkinson style combustion under cruise and light throttle and no need for an EGR at all!

quarterliterist > themushman 09/13/2014 at 17:09

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Why no mention of having it flow back into the pan, or what can happen if the oil water slurry in your catch can freezes, or even a proper air oil separator, vs a catch can?

Mercwri > themushman 09/13/2014 at 20:26

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A properly working PCV Valve shouldn't let this happen.

perkunas > themushman 09/14/2014 at 10:16

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My turbo volvo comes with a catch can which has an outlet back into the oil pan, so need to empty it. Doesn't just every car have it?

Plecostomus is a starred commenter > deekster_caddy 09/15/2014 at 03:05

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Turbocharged modern vehicles, namely any BMW that ends in 35i and nearly everything else with a turbo suffers from a good bit of blowby. There is a good sheen of oil inside my Fiesta ST's intake tube already and I have just 16k. Need to get that damn Mishimoto Catch can.

themushman > BJ 09/15/2014 at 08:01

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You can indeed get moisture in there. However, ive never noticed it to the extreme you mentioned. I suppose it is possible. But the most I have ever seen is a slight creamish film develop on top of the oil.

themushman > Biapilotaceman 09/15/2014 at 08:02

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Ill be honest, I am totally unfamiliar with Porsche. I really dont know much about them at all except Im too poor to ever own one

themushman > quarterliterist 09/15/2014 at 08:05

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Your PCV valve is a one way valve. The only way it can flow is out. The only water I have seen develop is light condensation and it separates on top of the oil. Unless your catch can is full to the top (since the inlet and outlet are at the top) within a minute or two of the engine running it would no longer be frozen and it wouldnt be an issue.

deekster_caddy > Plecostomus is a starred commenter 09/15/2014 at 09:17

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I will have to try this and see if it makes a noticeable difference on our VW. The intake and intake valves are notorious for getting gunked up. My gut says it's from the turbo itself, and has nothing to do with the PCV system, but it's worth exploring. (2008 Passat Wagon 2.0 TSI)

6cyl > Texican 09/15/2014 at 10:48

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I agree and if you read the second to last paragraph of the article then you will see why I made the comment I made.

BJ > themushman 09/15/2014 at 10:54

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Interesting. I just discovered the catch can a few weeks ago, and living in a climate with lots of temperature swings (above and below zero) and occasionally high humidity, it was a concern. Thanks!

Plecostomus is a starred commenter > deekster_caddy 09/15/2014 at 11:15

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With almost every turbo motor, there is SOME blow by. The more often you go WOT and get on it the more of it there will be. Do it and get back to us with how much you got out of it - I got a ton out of my old S70 GLT's turbo 5 after fitting it with a catch can.

themushman > BJ 09/15/2014 at 11:41

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As long as you keep up with emptying it, I wouldnt worry about it. The only way water can get in there is condensation. And condensation produces very little amounts of water in terms of volume. So with freezing temps, the biggest concern would be the lid of the catch can freezing solid so there no longer vacuum or a path for the air flow.

MontegoMan562 is a Capri RS Owner > themushman 09/16/2014 at 11:16

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I'm using the "spit that crap on the ground model" here:

functionoverfashion > themushman 11/05/2015 at 09:01

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This came up in my sidebar, despite being over a year old. Creepy, because I was just researching the PCV/catch can alterations people have done for my specific car last night. But it wasn’t even on the same computer.... creepy interwebz I think.

OMG, TTA! > deekster_caddy 11/05/2015 at 09:23

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If you’ve got oil entering your intake after the turbo, your turbo is leaking. PCV systems enter the intake before the turbo for obvious reasons (you’re not looking to pressurize your crankcase). My TTA (Grand National motor) has the PCV enter at the turbo intake bell housing, and the vertical intercooler acts as a catch can. I’ve considered adding a drain plug.

Jack Rumbaugh > themushman 11/05/2015 at 09:56

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I put one on my Challenger as soon as I got it due to all the recommendations on line. Very glad I did.

PowderHound > themushman 11/05/2015 at 10:17

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I run one of these Grimmspeed Air/Oil separators. Seems to work alright

SidewaysOnDirt still misses Bowie > MontegoMan562 is a Capri RS Owner 11/05/2015 at 10:27

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That’s always been my favorite. Let the beast mark its spot.

MontegoMan562 is a Capri RS Owner > SidewaysOnDirt still misses Bowie 11/05/2015 at 10:39

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man this post is old (I saw it in sidebar today too btw)

My engine bay looks soooo much better these days:

willconltd > themushman 11/05/2015 at 11:16

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Most emissions requirements are poorly thought out and implemented for short term goals that cause long term degradation to the cars they are supposed to clean up. I personally try to eliminate all the stupid emissions stuff. Things like cold start emissions are pointless. Why? They run for about 30 seconds and they dump excess fuel into your engine trying to heat up your cold catalytic converters. This is pointless everywhere, but probably even more so in the Southern states. In the BMW world where I am familiar with these things, it only runs if the car has been sitting idle for a day or so. So its stupid, and while it probably helps in the short term on new vehicles, in the long run it probably just hurts things.

Same for this PCV system. Stupid, causes more cleaning, and eventually leads to a dirtier engine that has the potential to pollute more than a clean one.

I am all for things that maximize fuel economy. Lets think rationally here, in the long term the best reduction in emissions is burning less fuel. A clean, well maintained engine burns less fuel per mile, so it pollutes less over time.

I think responsible upgrades like better flowing/performing catalytic converters is a good thing. I think everyone who maintains their engines should eliminate these unhelpful emissions systems that do more harm than good.

DaGimpster > themushman 11/05/2015 at 11:17

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Cobalt SS owner here (LNF), installed one of these babies on day 1 of ownership. DI solves a lot of stuff, but legacy PCV systems are no friend to you.

BoxerFanatic, troublesome iconoclast. > themushman 11/05/2015 at 11:59

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You missed one big point.

With modern direct-injected engines, this is more important... to the point where it might even be included as original equipment.

The oil in the intake tract is becoming an issue with direct injection, because the intake port is dry. The fuel isn’t present in the intake tract upstream of the intake valve, because the fuel is directly injected into the combustion chamber, independent of the valves.

The fuel doesn’t help cool the intake valves through atomization and evaporation off of the hot intake valve and intake port... so they remain quite hot. Plus the gasoline that usually acts as a solvent for carbonized solid oil remnants, and diluting agent for liquid oil, no longer does that.

The intake tracts with all that PCV oil and oil vapor, and the heat of the head bakes that oil into carbon scale that builds up on the back side of the intake valve, and the walls of the intake port, reducing it’s volume, increasing the intake valve’s mass (which the valve springs and cams aren’t calculated for) and reduces efficiency, as well as flaking carbon getting into the combustion chamber and scoring all of the surfaces in there, as well as being pushed out as carbon particulate emissions through the exhaust.

An air-oil separator becomes even more imperative on a direct injection issue, and car companies from VW to Mazda, and many others have had significant carbon buildup issues, which costs hundreds of dollars to clean up by tearing the engine cylinder head down and re-building it, if not the crankcase as well.

A high-quality, effective air-oil separator should be essential equipment from the manufacturer, and frankly should be equipped with a filtered and valved oil drain-back into the oil-pan, with the cleaned air ventilation going back into the intake tract.

An aftermarket solution that has to be manually drained of oil, while the oil level in the sump has to be supplemented is do-able, but the manufacturer should be able to do it better, and cycle that oil back through the oil filter, and the oil pump pickup for re-circulation and oil level maintenance.

Satoshi "Zipang" Katsura > deekster_caddy 11/05/2015 at 12:09

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Or an engine that has direct fuel injection. Eugh.

BoxerFanatic, troublesome iconoclast. > deekster_caddy 11/05/2015 at 12:13

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It is probably coming in through the PCV line, which might plug into the intake tract down-stream of the turbocharger, so not to soak the turbo compressor with engine oil, which could coke up the compressor.

Putting an air-oil separator, which is what a catch-can is, in the path of that vacuum line between the PCV valve and the intake tract port would prevent the oil from being circulated into the intake tract at all.

Although, if the intake tract port is down-stream of the turbo compressor, it may require re-locating the PCV one-way valve, so that turbo compressor boost pressure doesn’t back-flow your air-oil separator.

Theoretically, if the separator is really effective, the line port could be re-located to the vacuum/intake side of the turbo compressor, as the oil wouldn’t be a factor, and it would be drawing vacuum on the separator the whole time that the engine is running. The separator would have to be able to be effective at higher vacuum pressures, without getting overwhelmed and letting oil vapor flow through without being separated properly, as a turbo ingests larger volumes of air in order to pressurize the intake tract and combustion chambers.

themushman > functionoverfashion 11/05/2015 at 12:57

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That is weird. I got on jalop, saw i had like 10 notifications. I was like, did i post in my sleep last night or something, wtf? Must be a recent article related to a keyword in post or something.

functionoverfashion > themushman 11/05/2015 at 13:45

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We shall never understand the algorithms of Kinja.

Luc - The Acadian Oppo > themushman 11/05/2015 at 14:54

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SRT8’s were notorious for collecting oil in the intake. (previous Chally SRT8 owner here) and yes it is an absolute must on the 6.1L hemi. I was surprised by just how quick it would fill up.

John Doe > deekster_caddy 11/05/2015 at 16:51

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Not on most fords, especially 1984 onward with EEC-IV systems. Thats the only thing that gunks up the throttle body and Idle Speed Bypass solenoid. Carb cleaner works fine. Symptoms are erratic idle and slow accel from stop

Shoop > themushman 11/05/2015 at 17:22

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Uhh...uhhhhhh... i put a small air filter on mine, so i might have to change the filter every now and again when it gets oily, but it was cheap.

Skunk > deekster_caddy 11/05/2015 at 19:43

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Runaway Diesels! Awesome to watch.

AdamG8GXP > themushman 11/06/2015 at 16:18

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This actually adds to more maintenance, to empty it, and you’re risking voiding the warranty.

It seems like people do this mod just for the sake of modding when they run out of stuff to plastidip.

I never had any problems with this and none of my vehicles had catch cans. I’ve had 94 CHerokee, 4L six, 278000 miles when sold, 94 Lumina 3.1L six, w/ 143000 miles when sold, 96 Cutlass Supreme 3.1L six, w/ 149000 miles when sold, 2001 Lincoln LS 3.9L V8 w/ 110000 miles when sold, 95 LHS, 3.5L six 137000 miles.

If it was making anything better OEMs would put in it to avoid warranty claims but they don’t and have very long engine warranties these days.

jovimon7 > deekster_caddy 11/15/2015 at 09:36

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LOL about as environmentally friendly as a new VW!

Miata2016GT > themushman 12/27/2015 at 09:22

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This was not really stated in the article specifically, but... this is the huge problem with “sludging” on the 2.0L DI VW-Audi engines, and most other DI engines because the the oily gasses are not mixed with fuel-air mixture... just the air. A couple of threads are already going on Miata.net regarding these catch-cans for the Skyactiv engines. One of the companies showed the intake with a boroscope in the Skyactiv after just a few hundred miles... and I was shocked. I am on the fence about the install for warranty reasons. I am going to discuss it with my Mazda mechanic (he’s a Miata guy, racer, etc)

they-will-know-my-velocity > themushman 01/21/2016 at 09:32

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Doing a PCV delete on the GTO. Mainly to get rid of the snake nest of air and coolant hoses running all over this engine bay.

Mattbob > themushman 01/21/2016 at 10:07

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Great article. This will be my first project in the spring.

KusabiSensei - Captain of the Toronto Maple Leafs > themushman 01/21/2016 at 10:47

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If you can get away with it (i.e. your ECU doesn’t throw a code), you should also look at blocking the EGR system, since that, depending on the engine, can cause similar issues.

themushman > KusabiSensei - Captain of the Toronto Maple Leafs 01/21/2016 at 11:09

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Im all for EGR delete. Good point to bring up!

dieseldub > themushman 01/21/2016 at 14:42

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Good stuff! Also worth noting that this can help modern direct injected cars a lot as well.

What has become increasingly common in those vehicles is to have the intake ports and valves carbon up badly. The carbon is a product of oil from the crankcase vent system being exposed to combustion by-products and heat at the intake ports. There is valve overlap in the these engines, meaning the intake valves begin to open before the exhaust valve has closed completely and allowed all the combustion gases to exit via the exhaust. Part Of the reason for this is emissions. Many of these cars do not have an exhaust gas recirculation valve. The same effect of having an EGR is accomplished via the valve overlap.

On a port fuel injected car, not a big deal as the gasoline is injected right at the intake port. Being that gasoline is an excellent solvent, it does a decent job of keeping the carbon deposits to a minimum.

The problem enters when the fuel injector is removed from the port and inserted directly into the combustion chamber. Now you no longer have the cleaning effect of gasoline in the intake ports.

Direct injection is great for efficiency and power and allows for great increases in compression ratios and/or boost pressure. But it creates new problem areas...

Adding a catch can at least eliminates oil from the equation. This will at least greatly slow down the rate of carbon build in DI motors. There have been other findings as well that indicate certain very specific oil formulations seem extra resistant to allowing the carbon to form. Redline’s Group V esther-basestock oils appear to be one of them.

The oil catch can is still a good idea.

dieseldub > deekster_caddy 01/21/2016 at 14:47

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I can almost promise you that most of that oil does originate from the crankcase vent. Turbos can allow some oil to leak as they get tired, but on VWs it seems the vast majority originates from the CCV. And the CCV generally dumps the oil vapor and crankcase pressure into the inlet pipe just before the turbo. So many people mistake the oily residue seen in the turbo as being from the turbo when it actually originates from the CCV And is merely passing through the turbo.

I have opened up a few VW intercooler systems with CCV catch cans and they have almost no oil in there to note, which is in stark contrast with the stock system. There is a lot of oil in those!

DanZman > Shifty 01/22/2016 at 03:46

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I’ve been looking at adding one of those as part of my H/C/I/E build. Can I get a quick review?

Aaron M - MasoFiST > themushman 02/01/2016 at 09:30

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Three things:

First, you may as well check to see if your car has an air/oil separator built into the PCV system already. My car does, and since it’s NA adding an additional catch can will do absolutely nothing.

Second, if you’re collecting a lot of blowby in a low mileage, NA engine, it probably means the car was broken in poorly and the rings didn’t seat well. Street driven cars without turbos rarely need a catch can/oil separator which is why they don’t often come with one from the factory.

Third, the oil poisoning/octane lowering effect is relatively minor. Catch cans are/were popular in turbo engine tuning both because of the increased blowby and because the oil vapor effects were enough to mess up a dyno tune with all the factor of safety removed...but unless you’re running a very hairy tune, there won’t be anywhere near enough octane dilution to cause detonation. In Subaru tuning, for instance, catch cans are recommended because the oil in the intake tract coats the inside of your intercooler, which is significantly more of an issue than burning the oil itself.

Brazzzzzle > themushman 02/28/2016 at 23:09

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I believe, if your PCV system is working properly, it should not allow oil vapor to pass into the intake when there is low vacuum, that is, when the engine is under load, under heavy acceleration, which is when it could impinge on performance and cause detonation or other performance issues.

DavidHH > mcseanerson 03/14/2016 at 03:52

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Yes, because they already protect the engine with a little filter, one that traps the yuck from the PCV. On my Ford’s Windsor, it lives in the air cleaner housing. Fail to replace it and the oil clogs the air cleaner.

DavidHH > themushman 03/14/2016 at 03:55

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Sorry to argue with you, but the engine on my Audi 4000q has controlled ventilation of the crankcase, so basically it’s sucking a huge amount of air through it, and ingesting it and the blow-by into the intake. After about 350k miles, that Audi I-5 runs good, with one weak cylinder.

415s30 W123TSXWaggoIIIIIIo ( •_•))°) > themushman 04/06/2016 at 22:50

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I’ve thought about it, I have a breather on my Z but no can yet. Here is a nice one, I don’t know who makes this one, I don’t want one with any plastic on it. Good idea to mount it on the radiator there.

Gaseous Clay > functionoverfashion 05/27/2016 at 19:57

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It just came up for me again months later. Kinja is weird

JMV > themushman 11/14/2017 at 05:20

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Hi, good write up about this. Just I was thinking about the more power issue. I mean when blow by gasses are sucked back to engine and they are already burnt so they will decrease air volume in cylinders and that will decrease amount of fuel so wouldnt there be less air and fuel in the cylinders which will decrease performance? Not sure about how significant it would be but in theory it should have effect. Another thing i am wondering is that when oem pcv system is attached to intake so it has vacuum and it sucks blow by out from the crankcase and if u replace that with athmospheric system does it have enough performance to remove gasses so that crankcase pressure would not get too high?

MotorcarMuddman > themushman 08/31/2018 at 19:00

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Nope. Some of the article is correct but not all. You seem to be confused about a few things or at the least over generalizing. First the hose on the non pc v side of a “v” motor that goes from valve cover to an air intake tube almost never has vacuum and doe s not help put the system in a vacuum because it is in front of the throttle plate. Anything above/forward from your carb butterflies or throttle plate is non vacuum or barely registerable as vacuum. This side is a positive pressure vent like a failsafe if the pcv gets clogged before you start blowing gaskets. Secondly the glaringly obvious mistake is that if you put a filter on the line coming out of your catch can then your entire PCV system is not under vacuum and you will not draw any pressure out. It will then function just like the non PCV side that just allows excess pressure to naturally vent itself. Which is not enough on most engines and compressions nowadays. Plus that defeats the entire purpose of the can. If you have a proper catch can it will catch the oil and only allow clean air back into the intake/throttle body/carb which is where you get the vacuum required to pull the heavy oil/gasoline laden gases through the system. If vacuum was nt required they would just have filters/breathers on every valve cover opening and no pcv. Who let you write this article? Please stick to subjects you are more knowledgeable on. I like your writing style but not misinformation nor click bai ty bullshit titles.

dwightlooi > themushman 03/20/2019 at 20:34

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A CATCH CAN will not eliminate oil in the intake tract. It merely reduces it. And, depending on the can you use, sometimes not particularly effectively. Car manufacturers and their engineers are not idiots. They are aware of the issues related to oil and blow by particles in the intake. This is especially so in Direct Injection engines where they can build up into thick crud which progressively clogs the intake valves because no detergent in the gasoline ever get onto the valves unlike in port injected engines. So, most DI engine have oil separators under the valve covers ahead of the PCV valve. They are supposed to do what the Catch Can does. Their effectiveness, again, varies (VW-Audi ones are garbage to non-existent), but they are there. A Catch Can is simply a second round of separation. If you have a good engine, it won’t matter much if you have a catch can.

—

The problem with a Catch Can is that, unlike an OE oil separator under the valve cover which always drips oil back into the lubrication system, A catch can is a blocked off device. If you don’ t drain it and it gets filled to the brim, it can cause your PCV system to suck liquid oil instead of vapors straight into the intake. That is very bad.

MontanaJimmy75 > themushman 04/19/2020 at 12:35

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New to all of this and have a question about the PCV. Do you eliminate the PCV altogether by replacing it with a fitting or do you just plug your hose into it? Thanks for the great post, helps a lot on my decision!

Flash-G > BJ 08/08/2020 at 16:09

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HI , I live in Florida and i have a air oil separator on my car and it is very very Humid here in the summer and i have had no issues at all with it collecting any water , I check it about every two weeks and it works great just oil in the container , and this simple modification has helped a lot being my car has a GDI engine , This helps keep my valves clean and if you own or k now anything about issues with GDI the main issue is since it had direct injection is the fuel injection no longer sprays any gas onto the valves they get carbon build up very quick causing many harmful problems ..If you own a GDI engine this is a must modification its cheap very easy to install and will save you so much money ! and for people who are not good with working on cars its still very easy or have somebody do it ! For instance Hyundai dealers want there customers to come in every 10,000 miles for a valve cleaning for around 500.00 this is insane to me ! when a oil air separator is the answer for 20 to 100 tops i would think but just a 40-50 oil air separator..hope this helps also doing a valve clean yourself using Seafoam or any other brand will help i recomm end this before installing to help remove any carbon build up you already have...