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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.


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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.

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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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#2 ·
#3 ·
I believe this has been done on the Cruze by another member, but I forget who. The amount of oil that the catch can recovered was practically significant. I believe GM noted that if the car was burning or losing more than a quart of oil in a certain mileage (I don't remember the exact mileage, but it was at least 3,000), that it would need to be repaired under warranty.

Your results may vary in the Cruze. I'm looking forward to seeing how much oil that can recovers.
 
#4 ·
Yeah, I've seen the the other thread and that's where I got the ebay idea from. Local part store didn't have anything.

I'm actually more interested in the check valve to prevent pressurizing the valve cover. After experiencing the problems with the SRT-4 and the amount of oil in the TB that Markj2222 took pics of, I'm concerned since I'm running 22psi.

I was hoping to find some usable parts at good prices to offer kits for tuned members, but can't find anything. I ended up getting the same check valve I got for the SRT-4 which was $40 shipped.

I will monitor the levels and report back after 5000 miles.
 
#6 ·
Still looking for a good check valve that is under $15 shipped. Needs to open at 1in Hg.
Let us know what you find with regard to the check valve. I have a catch can that I want to install on my Cruze - looking forward to seeing your install/instructions.

I believe this has been done on the Cruze by another member, but I forget who.
If I recall the member is Smorey.
 
#7 ·
#8 ·
Im very interested in your findings.

I checked my intercooler for oil, there is a film coating the inside, but i used my vacuum pump to check the bottom of the intercooler and i didn't find a drop. Also in my upper charge pipe i found about a teaspoon of oil at the bottom.

Im going to get a catch can for sure, but first I want to see how well that ebay one performs.
 
#9 ·
Bought a catch can this weekend off ebay for $16. Need to get a check valve and it's going on the Cruze.
Looks just like the catch can I bought for my Cruze from e-bay, except I got a black one. Do you have a part # and supplier for the check valve?
 
#10 ·
Yeah they come in different colors but the black one was $20. I'll just plastidip mine.

I ended up getting this valve https://www.modernperformance.com/product/mpx_check_valve_8mm/neonsrt4_turbo_oilcatchcans. Shipping is absolutely ridiculous but I paid it anyway.

If you want to search for a cheaper solution, it needs to obviously be able to handle 30psi or more and needs to crack open at 1in Hg or less. I wasn't able to find any cheapo's that would open under 2in Hg (and that was low end for a range. They all said 2-4in Hg).
 
#12 ·
Yeah i'l break it down. I'm hoping to find a way to install it without cutting anything.
 
#13 ·
I ended up getting this valve https://www.modernperformance.com/pr...o_oilcatchcans. Shipping is absolutely ridiculous but I paid it anyway.

Thanks! Just placed my order. Yeah the check valve and shipping is pricey but for what I paid for the catch can, the whole system price is not bad. To put this in perspective I paid around $100 for a custom catch can for my GTO.
 
#15 ·
Do you need the check valve.

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#14 ·
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#17 ·
Cool well ill be intalling one also.

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#19 ·
Good ones come with a type of steel wool inside already and sealed shut. Lower quality ones use a mesh at the top and bottom to separate the oil from the vapor.
 
#22 · (Edited)
yes i have the catch can installed for about 8 months and about 8,000 miles and have on caught about 1oz of oil if that. One of the things i noticed is that the can gets pressuized when in boost. but there is a valve in the intake just under the pcv tube that limits the pressure. i think this has somthing to do with why i am getting so little oil. GM might of built the pcv system real good. I know on the srt-4's there pcv system sucks and they get alot of oil in the intake A LOT!! the whole system is set up on vacuum...thats all old school and not efficient at all. They pass the clean air act by .0063%.
Now what is this check valve you guys are talking about??
if we put that much pressure into the crank case the dip stick would blow out. the intake is setup by gm to handle anywhere from o 0 to 18psi stock.
 
#23 ·
Which catch can did you go with

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#25 ·
good to hear...now can he confirm that the way mine as well as others are hooked up right. it has not happen yet but i am waiting for the time when i am under boost and that lil can can't hold it and boom!!
 
#26 ·
If your can is under pressure then you have something wrong (if you hooked it up as he suggested). If you're hooking it up like I did in the OP, then you will get pressure because you don't have a check valve. Exact reason the check valve is there to prevent boost form going the wrong way.
 
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#27 ·
HAHAHAHA! Received my ebay catch can and it's completely empty! No mesh screens, no steel wool no nothing. I unscrewed the drain plug and looked inside. Hilarious.
 
#30 ·
#32 ·
42 Draft Designs

What do y'all think about these.

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I think I can think of 100 ways I'd rather spend $130-$235, even when it comes to catch cans. Aren't these usually a lot cheaper? I mean, I know you pay for quality and all, but that's pretty expensive.
 
#31 ·
I'm thinking the stealth version its a good price.

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#35 ·
Thinking about it more, I'd consider the ultimate or stealth over the one I bought if it was going to be under high pressure. Looks like it would hold up more vs a can with a clear view tube. But, the Cruze won't (shouldn't) have it under pressure, only vacuum.
 
#36 ·
I wouldn't spend more than $130 for one I just don't like putting cheap products on my car that I love so much.

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#37 ·
Finally installed my ebay special catch can. IMO don't bother purchasing it. Spend a bit more and get a nice one. The brackets are garbage and you have to hold it in place with a big hose clamp. But, that's what you get for $16.

Unfortunately there isn't a way (at least an easy way) to install the lines without cutting the existing PCV line. I tried for an hour to get the hose off the connectors. No dice. It's like they were heat shrink wrapped on there and it's one-way. So...I cut the line. I'll be buying a new one to keep around just in case i need to go in for service. Wonder how much that's going to cost :\

But, good news is that there was a crap ton of oil in my line. So the catch can will definitely be a helpful addition.
 
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#38 ·
i will be buying one before i tune for e85 and i will spend the $130 and get a good one.
 
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#39 ·
Unfortunately there isn't a way (at least an easy way) to install the lines without cutting the existing PCV line. I tried for an hour to get the hose off the connectors. No dice. It's like they were heat shrink wrapped on there and it's one-way. So...I cut the line. I'll be buying a new one to keep around just in case i need to go in for service. Wonder how much that's going to cost :\
Great! So will you be posting pictures of the install and providing a parts list? I am interested in placement and direction of the check valve in the "system".
 
#40 ·
No check valve installed yet. Since the PCV dumps at the top of the turbo inlet boost wouldn't get back into the PCV unless the throttle blades close and the BVP/BOV didn't open so there isn't a need for the check valve on the PCV lines at least the one for the crank case. I only see an evap line on the TB and that has nothing to do with the PCV. So the check valve may not bee needed at this point. I'll post about it if I find a place for it. It may just not be an issue with our cars.

As far as placement, I didn't want to drill any holes and all I could find was a single hole in the strut tower so I snaked my arm in there and stuck the bolt through and mounted the brackets that way. I'm displeased with it especially since I had to bolt two brackets together. But then again, it's a universal application. I will post some pics and do a write up next week probably. Placing it in the back corner of the passenger side of the car is the best place for it since you only need to remove a small section of the PCV hose.

I'm also not too happy about how I had to install the vacuum lines. They just went inside of the stock PCV hose, but clamps can't be used because it would crack the stock hose. It's a tight fit and should seal properly for now. When I order my stock PCV replacement, I'll probably cut more of the current one and replace the entire thing with new vacuum lines.
 
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#41 ·
help for a confused man here. Seems to me there are 2 ways to do this?
i. The way Vince suggests - to turbo inlet (not sure if a check valve required) &
ii. the way titan2782 suggests - to the intake manifold (check valve required)

I think this is a mod I would like to do prior to getting a tune, not sure which would be the better way to go.

Also found this catch can that seems to be a quality one. Anyone try this brand?

Thanks!
 
#42 ·
There is only one way. The PCV comes from the manifold and goes to the turbo inlet. The catch can goes on that line. I don't yet know if a check valve is needed in other areas of the system. I'm looking through the service manuals and I don't see anything. Based on what Vince said, I was thinking that there was another line (which he also said has a check valve already). But the catch can will be installed on the PCV line to catch oil for sure.

Part of the issue is I was making plans before fully understanding the way the system works on our cars. My bad on that. If I find an area that needs a check valve, I'll report it. But for now, save your money and just get the catch can.
 
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#43 ·
BTW Titan2782- really appreciate the info & upcoming DIY.
I used a breather on my civic & even though it was na, there was a surprising amount of oil that got caught. I'm sure this will prove to be a must have on tuned turbo motors. As i'm in CA as well, hope it's not too difficult to install/ take off

:nicetopic:
 
#44 ·
if i install mine i will never take it off. If Chevy ask Why its there? i will say. I was doing you all a favor by adding something to help prevent future damages.
 
#46 · (Edited)
Alright so I finally got around to redoing the catch can. The reason why is because about 2 weeks ago, I drained the can in my SRT-4 and it's only been in there for 3-4 months (with the tune). There was at least a cup of oil in there. The can was almost full.

Now, even though that ebay catch can didn't work out and actually caused damage, I was still ready to try something. So, I built one. Yup, from regular stuff you get at Home Depot.

Auto part Metal Material property Tire Muffler


Using 3/4 barbed fittings and some 3/4 fuel line, I attached it to the car using the ends from the old PCV line. There is incredible vacuum on the line and weak line with thin side walls will collapse. I started with some clear vinyl tube similar to what comes with the ebay can, but it collapsed at idle.

here it is installed

Vehicle Engine Auto part Car
Auto part Fuel line Engine Vehicle Car

So far so good. I've been driving with the tune on where ever I go so I'll check the oil levels in a month.

Note: My attachment quota is maxed I guess and the dropbox linked images aren't showing up so here are links to them for now
 
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