Dual Catch Can Skeptics - Look Inside
Thread Starter
Melting Slicks
Joined: Sep 2003
Posts: 2,458
Likes: 105
From: Northville Michigan
Dual Catch Can Skeptics - Look Inside
This evening after I got home from work I performed the first of my bi-annual oil changes.
In addition to draining 9 quarts of oil, removing two Mobil 1 M1-301 full-size filters, filling two new Mobil 1 filters, and adding 9 quarts of Mobil 1 0w40 oil, and two bottles of ZDDPlus; I also take the tops off of my two AMW catch cans to see if they have collected any oil.
This first picture shows the dual catch can setup and hose routing. The catch can closest to the cylinder head is plumbed into the PCV system. The catch can closest to the radiator is plumped into the line that on LS1 and LS6 engines comes off the passenger side valve cover and goes to the throttle body. Because I have a LS2 90mm throttle body, I do not have the connector on the throttle body to run the return line to. Therefore, I just vent the catch can to atmosphere.
This next picture is what the catch cans look like when they are empty. Note the four annual rings inside the cans.
This next picture shows the cans after I took the tops off this evening. Note that the PCV can is filled between the bottom and the 1st ring. Also note that the Valve Cover catch can is filled to between the 1st and 2nd ring.
Now, how did a catch can that 99% of C5 owners don't have end up with so much oil in it?
Why does this orphan catch can have more oil in it than the PCV system catch can?
Comments ?
In addition to draining 9 quarts of oil, removing two Mobil 1 M1-301 full-size filters, filling two new Mobil 1 filters, and adding 9 quarts of Mobil 1 0w40 oil, and two bottles of ZDDPlus; I also take the tops off of my two AMW catch cans to see if they have collected any oil.
This first picture shows the dual catch can setup and hose routing. The catch can closest to the cylinder head is plumbed into the PCV system. The catch can closest to the radiator is plumped into the line that on LS1 and LS6 engines comes off the passenger side valve cover and goes to the throttle body. Because I have a LS2 90mm throttle body, I do not have the connector on the throttle body to run the return line to. Therefore, I just vent the catch can to atmosphere.
This next picture is what the catch cans look like when they are empty. Note the four annual rings inside the cans.
This next picture shows the cans after I took the tops off this evening. Note that the PCV can is filled between the bottom and the 1st ring. Also note that the Valve Cover catch can is filled to between the 1st and 2nd ring.
Now, how did a catch can that 99% of C5 owners don't have end up with so much oil in it?
Why does this orphan catch can have more oil in it than the PCV system catch can?
Comments ?
Last edited by Pumba; Aug 5, 2008 at 10:01 AM.
Thread Starter
Melting Slicks
Joined: Sep 2003
Posts: 2,458
Likes: 105
From: Northville Michigan
Race Director
Joined: Dec 2000
Posts: 19,304
Likes: 85
From: San Diego CA
Under full-throttle conditions, the fresh air flow into the valve cover reverses, sending "dirty" blowby out the valve cover and into the throttlebody. The potential problem is that the catch can is designed for one-way operation. Once the flow reverses, oil in the can reservoir could be pulled through in the wrong direction. This is why you really shouldn't let the reservoir get too filled, Splashing of the oil also can lead to oil getting pulled out.
This is why you should either check often or use a glass catch can, as I do. In either case, try to keep the temperature of the "can" as low as possible. This'll help coalesce the airborn oil on the cooler surfaces.
BTW, did you check inside the intake side of each hose to see if there was any oil coating it?
This is why you should either check often or use a glass catch can, as I do. In either case, try to keep the temperature of the "can" as low as possible. This'll help coalesce the airborn oil on the cooler surfaces.
BTW, did you check inside the intake side of each hose to see if there was any oil coating it?
Tech Contributor
Joined: Jan 2007
Posts: 19,292
Likes: 1,109
From: Dyer, IN
What is the sequence of events between emptying the catch cans, and the next time you check and found oil present? A drive to work? A day at the track?
For some reason, I don't have these problems with oil in my pcv and fresh air intake lines....
http://www.flickr.com/photos/1545929...88571/sizes/l/
For some reason, I don't have these problems with oil in my pcv and fresh air intake lines....
http://www.flickr.com/photos/1545929...88571/sizes/l/
Last edited by lucky131969; Aug 4, 2008 at 10:53 PM.
Race Director
Joined: Oct 2002
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From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
You are correct though about flow reversal of the fresh air inlet at WOT. We all know the manifold vacuum disappears (which is normally what draws the fresh air into the crankcase), but there is still substantial pressure being developed in the crankcase (even without significant ring blowby) during high rpm.
He has a smart setup, but if merely venting the engine to free air, the only need for the second can is to gauge how much oil he'd have simply blown out into the air. I would hope he's not reusing that collected oil,
Race Director
Joined: Dec 2000
Posts: 19,304
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From: San Diego CA
Ah, good catch (no pun intended) about the LS2! The flow can still reverse through the wrong end of the can, however. That's why I was wondering if any oil can be seen in the hose leading back to the valve cover.
Tech Contributor
Joined: Jan 2007
Posts: 19,292
Likes: 1,109
From: Dyer, IN
I'm impressed at the system in place to ensure adequate oil, and cooling of said oil, to the engine. Considering you are auto-xing this car, I'm amazed that you rely on two 3/8 lines to adequately vent the crankcase under such heavy load.
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St. Jude Donor '06 & '12
By venting to atmosphere, your negating the PCV all together. If you connect the fresh air port to a p0int before the throttle blade, you will decrease the amount of oil in your fresh air can. I also run a 2 can setup on my high compression LSx454. I did exactly what you did in the beginning, and got your exact same results. When I tapped my intake before the TB it all but went away. Your PCV NEEDS the fresh air pulses to aid in evacuation. Yes, your pcv system all but stops working at WOT, but thats significantly less that part throttle driving when vacuum is not only the highest, but the pcv is sucking the most oil. By creating a positive pulse when the throttle blade closes, it aids in the sucking effect.
But it also doesnt help with your oiling system as well.
You should look into some oil restricting pushrods. Your probably pumping wayyyy to much oil into your valvetrain.
But it also doesnt help with your oiling system as well.
You should look into some oil restricting pushrods. Your probably pumping wayyyy to much oil into your valvetrain.
Thread Starter
Melting Slicks
Joined: Sep 2003
Posts: 2,458
Likes: 105
From: Northville Michigan
