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Oil catch can explained (read if tuned)

38K views 54 replies 13 participants last post by  USPI2011 
#1 · (Edited)
Thought I'd put up some info even though it isn't on the cruze (yet) since some members are seeing oil in their charge pipes.

Basically what happens is there is a Positive Crankcase Ventilation (PCV) valve that allows vapors in the crank case (where your oil sits) to be vented back into the intake

The blowby vapors that end up in an engine's crankcase contain moisture as well as combustion byproducts and unburned fuel vapors. The crankcase is sealed to prevent the escape of these gases into the atmosphere, but the vapors must be removed to prevent oil contamination that leads to sludge formation. The positive crankcase ventilation (PCV) system siphons these vapors from the crankcase and routes them into the intake manifold so they can be reburned in the engine.


but what can happen is oil can also escape and get into the intake. Sometimes it will make it's way into the cylinders and cause blue smoke to come out of the tail pipe and gunk up the motor. Since oil has a low octane rating, it will cause knock/detonation which is the premature combustion of the compressed air/fuel mixture. sometimes this can be heard as an audible "ping" like there are pennies rattling inside the engine.

To prevent this, there is a device called an "Oil Catch Can" and it's purpose is to take in the air/oil coming from the PCV valve and capture the oil while letting the vapors continue into the intake for burning.

This is the catch can I bought for my SRT-4. It's a nicer one, but it's pretty much universal.

Electronic device Technology Gadget Auto part Muffler


It has two ports, one for the line in from the PCV and another for the line to the throttle body/intake manifold.



it also has a release valve on the bottom for quick draining. Also on the side is a clear tube that gives a quick visual of how full that thing is.


Watch Auto part


The way it works is it has a divider wall on the inside and both sides are stuffed with steel wool. Vapor goes in and out while oil stays in.

High boost setups

In high boost setups (basically anything beyond stock settings), you get what's called pressurizing of the valve cover. This happens under high boost and is caused by the boost pressure going in the wrong direction up the PCV line and forcing its way past the PCV valve and into the valve cover. What happens then? Well there could be a few things like oil being forced past valve seals and down into the head(s) and back into the cylinders (read above) but the most common is that the pressure exits through the vent. Most vehicles have vents in the valve cover and surprisingly, a lot of them do not have shrouds to prevent oil from escaping. The vent serves a similar purpose as the PCV, allowing for pressure to escape and are usually piped directly into the intake again (for emissions reasons). In the V style motors like the V6 and V8, it's common for people to remove the PCV and put a breather which looks like a tiny K&N filter on top of one or both valve covers.

anyway, the pressure from the boost getting past the PCV causes oil to fly out of the vent or keep the crank case/valve cover under pressure (which is bad all around). To prevent this, a 1-way check valve is placed in between the throttle body/intake manifold and the catch can. While you can install a check valve without a catch can, it isn't recommended as your check valve will get oily and fail (usually from getting clogged by oil). What the check valve does is allows air to flow only in one direction and not the other. so when installed correctly, the pressure from the boost will not get past the check valve and thus, cannot get into the valve cover and cause problems.

Vehicle Engine Auto part Car Compact car


This is the engine bay of my SRT-4 (yes, it's filthy and it needs some attention). The green line starts at the top of the valve body and runs down to just behind the throttle body. The green circle is the vent that goes right back into the cold side intake pipe.

Auto part Engine Fuel line Automotive fuel system Automotive engine part


This is the result of too much boost. This is a picture of the cold side (pre-turbo). There is a bit of oil sitting there waiting to get sucked into the turbo compressor wheel. I actually cleaned this out last week (had a ton in there) so you can see what happens in just a few days.

As for some of our members who are seeing it at the throttle body, I would make a guess that boost is pressuring the valve cover and as soon as the boost goes away, the pressure goes back out the PCV (along with oil).

Engine Auto part Vehicle Fuel line Car


I've installed the catch can here with the line coming from the PCV and then going to the throttle body.The cylinder in the middle of the line going to the throttle body is the 1-way check valve.

The point is, turbo cars are a PITA, have ton's of vacuum lines every where and require special attention and upgraded systems when making modifications.

This catch can was $110 but catch cans can be had for $25 if you look. Very easy to install. I'll be getting one for the Cruze (not sure if I'll drop $110 on one of these, but maybe).

You're supposed to empty the can or replace it with each oil change.

I hope you find the informative. I'll do a specific write up for the Cruze when I get a system for it.

Please note that installing a catch can cause you to fail visual inspection when trying to get smogged.
 
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#48 · (Edited)
Cleared out some attachments and updated the post to include the photos. Had some black 3" plastic pipe, grabbed two end caps (looked like I was making a pipe bomb and got some strange looks!), 2 3/4 barbed brass fittings and some various brass fittings to make a draining component. I couldn't find anything nicer like a valve to use so just improvised.

Overall it looks hackish but once I make sure it's working I'll pull it out, paint it up nice and attach it with a nice hose clamp instead of a zip tie ;) I also left in the stock PCV tubing incase I need to pull over and swap it back in real quick. I'll remove that later as well.
 
#51 ·
Did you install any kind of mesh or grate in the home made can? If it is empty it will be no better than the ebay catch can.

Examples;
I'm going to disagree with you, but only 1/2 way. A good design that puts the inlet below the outlet and a long body should be sufficient for keeping from entering the outlet. From what I've seen, the pcv system is under vacuum, the turbo is sucking air from the engine. I don't yet know what happens under boost at this point, but assume that pressure will equalize in the lines.

Now, if the suction is strong enough to draw the air and oil into the outlet from the inlet (or the bottom of the tank even) then something else has to be in place to help this. If it's a screen, then what will happen is that the oil is only slowed down from entering the outlet, but since the system is under constant suction, the oil will not have time to fall into the container, but will just be pulled up into the outlet. So it's no different than not having a screen.

There are a few ways we could approach this, adding a tube that goes from the inlet to the bottom of the tank to give distance between the inlet and outlet making it harder for oil to get sucked upward into the outlet, but when under pressure, that tube could allow for caught oil to swirl and get spun around and end up in the outlet. Based on my previous experience with the ebay can which had a an inlet and outlet the size of a BB, I suspect that this is a good possibility.

The other consideration is the effect of adding resistance to the line. In this case, I don't think it would really cause a problem because the turbo would be unaffected and any pressure from the engine to the can could still force oil downward.

The other option is to do what the manufacturers for the catch can I put on the SRT-4 did and fill it with a course steel mesh. This adds too much resistance I think for our application and would only serve to clog the entry and exit or at least provide a way for the oil to stick around and get sucked into the outlet.

I gave a lot of consideration to the design, adding screens and mesh and other features. I decided to start off with an empty canister and see what happens. If you remove the ducting from the air box to the turbo inlet, you will see a very obvious hole where the pcv hooks up and it will have oil, even if only a small amount, sitting there. Regardless of the amount of oil caught by the can, I want to eliminate any oil or reside from entering the turbo.

Now, as far as any vapors that come through that tube, I don't know how to help that without diminishing the effectiveness of the pcv system and not causing another major repair.

I'll go check my turbo right now and I'll check it again in a month. If there is still residue, I'll add the screens and some other "filtering" features.
 
#52 ·
The oil coming from the crank case is going to be hot and in an almost vapor form. It will stay in this state for the most part until the catch can, or after, where it can start to hit air and cooler components allowing it to go to a completely liquid form. Liquefying before the catch can will only help the can do its job.

The screens don't work by slowing the oil down. The oil hits the screen and gathers on it enough to cause the oil to drop to the bottom of the tank, where it will be cool and heavy enough to not get sucked through the screen. Typically good catch cans have 2 or 3 layers of filtering, with the minimum being a screen or mesh of some kind.

To each his own, and I give you credit for making your own and going through the effort. Take my opinions as just that.
 
#53 ·
The oil coming from the crank case is going to be hot and in an almost vapor form. It will stay in this state for the most part until the catch can, or after, where it can start to hit air and cooler components allowing it to go to a completely liquid form. Liquefying before the catch can will only help the can do its job.
The oil will never get hot enough to vaporize (~250* C). If it does, there are other problems. The vapors will be from exhaust and unburnt fuel coming into the crank case via the piston rings. I do agree that cooling the oil before it gets to the can would improve it's function, but there isn't enough distance between the valve cover and the can.

The screens don't work by slowing the oil down. The oil hits the screen and gathers on it enough to cause the oil to drop to the bottom of the tank, where it will be cool and heavy enough to not get sucked through the screen. Typically good catch cans have 2 or 3 layers of filtering, with the minimum being a screen or mesh of some kind.
Yes, they work by helping to keep the oil in it's place. What I said was that in our application, the screen will only serve to slow the oil down, but also to keep it in a place where it can still be sucked up. They will be just about useless in normal design. The cans you refer to and even the one I purchased for the SRT-4 were designed for what I call "normal" PCV function and do not consider our applications which are of a different design. I'm only familiar with 2005 and earlier turbo applications and 2006+ non turbo setups. The way to cruze is setup (1.4T only) is different and the same rules don't apply.

To each his own, and I give you credit for making your own and going through the effort. Take my opinions as just that.
I appreciate the input, no doubt. I just checked the turbo and so far no oil. But, it's only been about 250 miles. I'll check back in in another 500 miles.
 
#55 ·
Thought I'd put up some info even though it isn't on the cruze (yet) since some members are seeing oil in their charge pipes.

Basically what happens is there is a Positive Crankcase Ventilation (PCV) valve that allows vapors in the crank case (where your oil sits) to be vented back into the intake



but what can happen is oil can also escape and get into the intake. Sometimes it will make it's way into the cylinders and cause blue smoke to come out of the tail pipe and gunk up the motor. Since oil has a low octane rating, it will cause knock/detonation which is the premature combustion of the compressed air/fuel mixture. sometimes this can be heard as an audible "ping" like there are pennies rattling inside the engine.

To prevent this, there is a device called an "Oil Catch Can" and it's purpose is to take in the air/oil coming from the PCV valve and capture the oil while letting the vapors continue into the intake for burning.

This is the catch can I bought for my SRT-4. It's a nicer one, but it's pretty much universal.


View attachment 10435

It has two ports, one for the line in from the PCV and another for the line to the throttle body/intake manifold.


View attachment 10437

it also has a release valve on the bottom for quick draining. Also on the side is a clear tube that gives a quick visual of how full that thing is.


View attachment 10436

The way it works is it has a divider wall on the inside and both sides are stuffed with steel wool. Vapor goes in and out while oil stays in.

High boost setups

In high boost setups (basically anything beyond stock settings), you get what's called pressurizing of the valve cover. This happens under high boost and is caused by the boost pressure going in the wrong direction up the PCV line and forcing its way past the PCV valve and into the valve cover. What happens then? Well there could be a few things like oil being forced past valve seals and down into the head(s) and back into the cylinders (read above) but the most common is that the pressure exits through the vent. Most vehicles have vents in the valve cover and surprisingly, a lot of them do not have shrouds to prevent oil from escaping. The vent serves a similar purpose as the PCV, allowing for pressure to escape and are usually piped directly into the intake again (for emissions reasons). In the V style motors like the V6 and V8, it's common for people to remove the PCV and put a breather which looks like a tiny K&N filter on top of one or both valve covers.

anyway, the pressure from the boost getting past the PCV causes oil to fly out of the vent or keep the crank case/valve cover under pressure (which is bad all around). To prevent this, a 1-way check valve is placed in between the throttle body/intake manifold and the catch can. While you can install a check valve without a catch can, it isn't recommended as your check valve will get oily and fail (usually from getting clogged by oil). What the check valve does is allows air to flow only in one direction and not the other. so when installed correctly, the pressure from the boost will not get past the check valve and thus, cannot get into the valve cover and cause problems.

View attachment 10438

This is the engine bay of my SRT-4 (yes, it's filthy and it needs some attention). The green line starts at the top of the valve body and runs down to just behind the throttle body. The green circle is the vent that goes right back into the cold side intake pipe.

View attachment 10439

This is the result of too much boost. This is a picture of the cold side (pre-turbo). There is a bit of oil sitting there waiting to get sucked into the turbo compressor wheel. I actually cleaned this out last week (had a ton in there) so you can see what happens in just a few days.

As for some of our members who are seeing it at the throttle body, I would make a guess that boost is pressuring the valve cover and as soon as the boost goes away, the pressure goes back out the PCV (along with oil).

View attachment 10440

I've installed the catch can here with the line coming from the PCV and then going to the throttle body.The cylinder in the middle of the line going to the throttle body is the 1-way check valve.

The point is, turbo cars are a PITA, have ton's of vacuum lines every where and require special attention and upgraded systems when making modifications.

This catch can was $110 but catch cans can be had for $25 if you look. Very easy to install. I'll be getting one for the Cruze (not sure if I'll drop $110 on one of these, but maybe).

You're supposed to empty the can or replace it with each oil change.

I hope you find the informative. I'll do a specific write up for the Cruze when I get a system for it.

Please note that installing a catch can cause you to fail visual inspection when trying to get smogged.
Great explanation now I hope Cruze inthuziast will get a better understanding of backwards gm engineering. LOL
 
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