Oil Catch Can and Blow-by

acsak

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I've got a question about the oil that's "caught" in these cans. Seems like most people are dumping it but would there be any danger in simply returning it to the crank case? Say every 2k-3k miles you drain it directly into the oil filler neck?

If we can expect to draw as much as TKL223/3 is showing every 200 miles, it seems to me that simply dumping that oil would mean we're running an ever decreasing amount of oil until we change it and bring it back up to the required level.
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JDJL

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I've got a question about the oil that's "caught" in these cans. Seems like most people are dumping it but would there be any danger in simply returning it to the crank case? Say every 2k-3k miles you drain it directly into the oil filler neck?

If we can expect to draw as much as TKL223/3 is showing every 200 miles, it seems to me that simply dumping that oil would mean we're running an ever decreasing amount of oil until we change it and bring it back up to the required level.
Not a good idea. There's fuel and other crap mixed with the oil from the catch can. You don't want to add that back to your crankcase.
 

zakaron

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Let's remember where this started from...
Years ago, before the emissions push of the '70s, engines vented the crankcase to the air. It was determined that this was bad for the environment, so manufactures came up with the PCV system. This allowed those freed hydrocarbons to get recycled and burned. It was a simple cheap solution that met regulations and required no user intervention. Win all around for the auto maker who kept the system for decades.

So why is there a problem? The problem lies when too much oil is picked up in blow by and starts coating the entire intake track. Normally not a problem, but when electronic IAC valves came into play, that oil buildup cause them to stick. Ask me how many times I've pulled & cleaned it from cars over the years. Direct injected engines saw a new problem with the infamous carbon buildup that manufactures have been dealing with now. Audi mostly corrected this in their 3.0 V6T engine with a built in oil separator on the PCV system right under the supercharger. Guess what, this acts just like a catch can, but dumps the oil back into the crankcase so end users do not have to worry about emptying it.

Again, for multiport fuel injected systems, not normally a problem unless you start getting too much oil ingested. This oil burns and coats the piston crown - if you've ever torn down a high mileage engine that started consuming some oil, you'll see what I mean. This leads to hot spots that in turn cause pre detonation, aka knock & ping. I used to have an occasional ping at lower RPM on my GTO. Tried Seafoam and making sure all sources of vacuum were tight. After running a catch can for several thousand miles I noticed much less ping.

This leads me to another point. That oil mist mixing with the vaporized gasoline will actually lower octane rating. By scrubbing the PCV gasses before hand, you get less oil mixed with the gas and ever so slightly "purer" fuel mix entering the cylinder.

One thing that strikes me interesting is how they got this Pentastar to run 11.3:1 CR on 87 octane as a non-direct inject system. Heavy tuning to pull timing, but if some engines pull more oil from the factory, this could cause the all the ping issue posts I keep reading about.

TL;DR - there are benefits to a catch can; I have first hand experience with stopping a ping condition and not clogging my IAC on the GTO. *However*, the benefits are really only going to be seen with high mileage as the engine seal tolerances start wearing on the sloppy side. Will your engine fall apart at 100K without one? No. Will it run more efficiently at 200K? Probably.
 

Rodeoflyer

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Spot on brother.
 

AnnDee4444

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I used to have an occasional ping at lower RPM on my GTO. Tried Seafoam and making sure all sources of vacuum were tight. After running a catch can for several thousand miles I noticed much less ping.

This leads me to another point. That oil mist mixing with the vaporized gasoline will actually lower octane rating.
It could also mean that more carbon was built-up on the piston, resulting in a higher compression ratio.
 

Rodeoflyer

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That would take a ton of carbon buildup.. most likely the carbon deposits causing the pre-ignition. It would burn long before it built up enough to cause an increase in comp.
 

Rodeoflyer

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This is what occurs... cause of pre-ignition involves excessive carbon buildup inside of the cylinder. This buildup can form a heat barrier, making it more difficult for the cylinder to diffuse the heat of combustion. As the engine continues to heat up, eventually the carbon buildup retains enough heat to cause premature combustion.
 

Rodeoflyer

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SteadyC

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I have the UPR, happy that I did this as I do intend to keep the Jeep for a while. what I can say is, the crap that I pour out every couple of thousand of miles, I am very happy knowing isn’t being recycled back into the heads and coating my valves, etc. the stuff is nasty. It just goes into my dumped oil during oil changes.
 

mwilk012

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I have the UPR, happy that I did this as I do intend to keep the Jeep for a while. what I can say is, the crap that I pour out every couple of thousand of miles, I am very happy knowing isn’t being recycled back into the heads and coating my valves, etc. the stuff is nasty. It just goes into my dumped oil during oil changes.
Gas sprays over your valves. It doesn’t stick.
 

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I’m a fan of my UPR. I’ve pulled almost 14oz of oil out since the first week of January. I did an oil change in January at 20k miles, one in end of April at 25k, and do one in 1,200 miles at 30k. I do all of my own oil changes and one of the free oil changes once a year at the dealer so I know the oil amount is correct. Just make sure to dump it once a month.
Very easy to drain takes 1 min to unscrew pour out and put back on.

7F285793-16AE-47A5-8CC9-1A6957215EFD.jpeg
 

Jeepin' John

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This leads me to another point. That oil mist mixing with the vaporized gasoline will actually lower octane rating. By scrubbing the PCV gasses before hand, you get less oil mixed with the gas and ever so slightly "purer" fuel mix entering the cylinder.

One thing that strikes me interesting is how they got this Pentastar to run 11.3:1 CR on 87 octane as a non-direct inject system. Heavy tuning to pull timing, but if some engines pull more oil from the factory, this could cause the all the ping issue posts I keep reading about.
Referring to low speed pre-ignition, my conspiracy theory is that it has become a new problem due to using 0w-20 weight oil. The oil is thin enough to get into the cylinder in larger quantities, to the point that it is affecting combustion and causing knock

High engine compression would make more PCV line pressure right? And thinner oil would flow through it easier, and even overcome a good catch can. Might be why i'm seeing oil make it though my mishimoto at the intake manifold clean line.

And if you're combining PCV oil in the cylinder as well as the oil coming by the piston rings in a larger amount into the cylinder, you've got a good amount of oil that is being compressed in a high compression engine with the fuel. Seems like that could be causing the low-speed pre-ignition.

that's my uneducated theory - could be totally wrong, just thinking out loud for the guys who know more about this stuff
 

mwilk012

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Referring to low speed pre-ignition, my conspiracy theory is that it has become a new problem due to using 0w-20 weight oil. The oil is thin enough to get into the cylinder in larger quantities, to the point that it is affecting combustion and causing knock

High engine compression would make more PCV line pressure right? And thinner oil would flow through it easier, and even overcome a good catch can. Might be why i'm seeing oil make it though my mishimoto at the intake manifold clean line.

And if you're combining PCV oil in the cylinder as well as the oil coming by the piston rings in a larger amount into the cylinder, you've got a good amount of oil that is being compressed in a high compression engine with the fuel. Seems like that could be causing the low-speed pre-ignition.

that's my uneducated theory - could be totally wrong, just thinking out loud for the guys who know more about this stuff
Any evidence that oil consumption is up on engines using 0w-20? In my experience, it’s never the oil’s fault. Poor PCV design is most oil consumption that is considered “normal”.
 

LittleDog

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Referring to low speed pre-ignition, my conspiracy theory is that it has become a new problem due to using 0w-20 weight oil. The oil is thin enough to get into the cylinder in larger quantities, to the point that it is affecting combustion and causing knock

High engine compression would make more PCV line pressure right? And thinner oil would flow through it easier, and even overcome a good catch can. Might be why i'm seeing oil make it though my mishimoto at the intake manifold clean line.

And if you're combining PCV oil in the cylinder as well as the oil coming by the piston rings in a larger amount into the cylinder, you've got a good amount of oil that is being compressed in a high compression engine with the fuel. Seems like that could be causing the low-speed pre-ignition.

that's my uneducated theory - could be totally wrong, just thinking out loud for the guys who know more about this stuff

Wait, I keep 5W30 in the jeep in the summer, it even says 5W30 on the cap. 2.0T Etorque.

I *might* put a thinner grade in the winter, unless the warranty people are watching.
 

jbcrane

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Let's remember where this started from...
Years ago, before the emissions push of the '70s, engines vented the crankcase to the air. It was determined that this was bad for the environment, so manufactures came up with the PCV system. This allowed those freed hydrocarbons to get recycled and burned. It was a simple cheap solution that met regulations and required no user intervention. Win all around for the auto maker who kept the system for decades.

So why is there a problem? The problem lies when too much oil is picked up in blow by and starts coating the entire intake track. Normally not a problem, but when electronic IAC valves came into play, that oil buildup cause them to stick. Ask me how many times I've pulled & cleaned it from cars over the years. Direct injected engines saw a new problem with the infamous carbon buildup that manufactures have been dealing with now. Audi mostly corrected this in their 3.0 V6T engine with a built in oil separator on the PCV system right under the supercharger. Guess what, this acts just like a catch can, but dumps the oil back into the crankcase so end users do not have to worry about emptying it.

Again, for multiport fuel injected systems, not normally a problem unless you start getting too much oil ingested. This oil burns and coats the piston crown - if you've ever torn down a high mileage engine that started consuming some oil, you'll see what I mean. This leads to hot spots that in turn cause pre detonation, aka knock & ping. I used to have an occasional ping at lower RPM on my GTO. Tried Seafoam and making sure all sources of vacuum were tight. After running a catch can for several thousand miles I noticed much less ping.

This leads me to another point. That oil mist mixing with the vaporized gasoline will actually lower octane rating. By scrubbing the PCV gasses before hand, you get less oil mixed with the gas and ever so slightly "purer" fuel mix entering the cylinder.

One thing that strikes me interesting is how they got this Pentastar to run 11.3:1 CR on 87 octane as a non-direct inject system. Heavy tuning to pull timing, but if some engines pull more oil from the factory, this could cause the all the ping issue posts I keep reading about.

TL;DR - there are benefits to a catch can; I have first hand experience with stopping a ping condition and not clogging my IAC on the GTO. *However*, the benefits are really only going to be seen with high mileage as the engine seal tolerances start wearing on the sloppy side. Will your engine fall apart at 100K without one? No. Will it run more efficiently at 200K? Probably.
Thank you for this summary. New guy here, learning as I go. I’d never heard of a catch can. It seems in so many topics usually two camps emerge : “you don’t really need to do that” and “I always do that.” I’m one of those guys that believes in small things over long spans of time can matter. After reading through this thread I’m thinking it sounds like a good idea. Also thinking of a cold air intake because I like the thought that whatever can be done to help things run more efficiently should be done (If I read correctly you do not necessarily need to cut the vent in the hood, reducing the risk of water intake).

Thanks everyone for being willing to share your knowledge and candid opinions.

Recommendations for best in class catch can solutions? Thanks again.
 
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