PCV oil separator - build it?

Heads, valves, pistons, rods, crankshaft, etc...

Moderators: Helpinators, Moderators

Post Reply
SubaruCO
In Neutral
Posts: 23
Joined: Fri Apr 04, 2003 11:54 pm
Location: Denver, CO

PCV oil separator - build it?

Post by SubaruCO »

After searching I found this topic has not been brought up in while, so I thought I might pose some more questions, facts and theories (my opinions of course).

In the process of cleaning the engine bay, and doing away with unneccsary items (saving weight) I came across the PCV system. Subaru’s system seems to have two separate objectives. First it is to increase piston ring seal by evacuating the crankcase and reduce inertial losses by creating vacuum in the crankcase and valve covers. Second it is plumbed back into the intake for emissions reasons (secondary to vacuum of course). The problem seems to come from the vacuum pulling oil mist created by the rotation of the moving crank and cams. I would imagine this would not be a big deal in terms of detrimental effects of oil in the intake except that Subarus seem to have either higher vacuum, higher crankcase pressure or more of an oil misting issue than other engines I have worked on. It could also be that the PCV pickup off the crank is in a poor location. What this all adds up to is a lot of oil deposits in the intake. I’m not sure this creates much of an issue except in the long run where evaporated deposits could gum up injectors or valves and create hot spots (not to mention taking up valuable O2 volume!) Turbo cars suffer from the intercooler losing some heat exchange capability.

I removed the hoses connecting the valve covers to the PCV circuit capped the connector and replaced the valve cover outlets with breathers. The crankcase hose I left in place, but now have noticed even more oil on the PCV valve than before. I would like to engineer an oil separator for this vacuum circuit and was wondering if anyone had done something similar.

mile hi seems to have a system on his, though I do not know the details (conveniently he seems to live in the same town). If I can build one soon I will detail all the parts and build process so it can be shared here. Thanks for your help.
Marshall Jung
92 Legacy 5MT (Home Depot Edition)
ciper
Knowledgeable
Knowledgeable
Posts: 4388
Joined: Tue Oct 15, 2002 8:16 pm
Location: SFCA

Post by ciper »

Here is a design I helped someone make.

A can with a screen at the bottom, steel wool above the screen then a small amount of ball bearings above that. Input from the valve covers would enter near the bottom, outlet would be at the top. A drain would have to be on the very bottom of the can.

The ball bearings would weight the wool down and also provide a large surface area for oil to stick to. Oil would accumulate at the bottom.
SubaruCO
In Neutral
Posts: 23
Joined: Fri Apr 04, 2003 11:54 pm
Location: Denver, CO

Built it.

Post by SubaruCO »

So I finished building an oil separator and replumbing the breathers for the valve covers. Of course, I don't have any pictures of this yet, so in reality this post is of little value. Yet I will at least describe the parts used so that if any others want to undertake this you will have some initial ideas.

I used a Moroso oil separator/breather sourced from Summit Racing (yes, it is meant for a doh-mestic V-8 and it does look big on Subaru's flat-4) and it cost all of $7.00. While there are probably more expensive sytems out there this one installs right inline with the existing PCV hose connections and is pretty unobtrusive (probably even more so if anything Summit sold was available in any other color but chrome).

After recieving the oil separator I obtained some high temp PVC hose in 3/8" and 1/2" and some common hose clamps. 1/2" runs from the crankcase outlet to the bottom of the oil separator and 3/8" runs from outlet to the PCV valve on the intake. The oil separator has to be mounted vertically to allow draining so you'll have to engineer (read fudge) with the lengths to get the alignment. After clamping everything down the oil separator is light enough that it does not have to be mounted separately and after driving around (driving hard, of course) the new PCV valve is still clean and oil free though I'll grant you that more time is needed to evaluate. Time will tell if this is an effective setup.

As to the replumbing of the breather setup: 3/8" PVC hose connects each valve cover outlet with the breather element (looks like a miniature cone air filter) which is mounted to one of the AC routing brackets (no AC on mine though). Routing and location is personal preferance.

One of these days I'll get a digital camera and then I'll post some pics. Until then if you have any questions please ask.
Marshall Jung
92 Legacy 5MT (Home Depot Edition)
czo79
Second Gear
Posts: 466
Joined: Mon Jan 20, 2003 9:11 am
Location: Montpelier, VT

Post by czo79 »

do you have any suggestions on where to get breather filters online? I need to pick up a couple. Does the crankcase breather have air going both in and out like the valve cover ones? Or does the air just exit the crankcase one? Do you worry about the air entering/exiting the engine that isn't being measured?
Thanks
Micum
Micum
91 Legacy Turbo Sport - 94 JDM EJ20G
97 Legacy 2.5 GT - mod'd
93 Impreza L AWD (sold)
97 Legacy 2.5 GT (deceased)
98 Legacy Outback (sold)
ciper
Knowledgeable
Knowledgeable
Posts: 4388
Joined: Tue Oct 15, 2002 8:16 pm
Location: SFCA

Post by ciper »

You are letting extra air into the intake after the AFM with this setup. The valve covers are connected to the crank so when at closed throttle (high vacuum) you will pull air into the valve cover gasket breathers and into the intake.

You will also end up with an oil/dust film all over the engine bay with it vented.
SubaruCO
In Neutral
Posts: 23
Joined: Fri Apr 04, 2003 11:54 pm
Location: Denver, CO

Post by SubaruCO »

Hmmm...not sure exactly what you mean ciper, though I can say that I have taken into account all the vaccum routing and carefully capped or removed all extra inlets no longer used by the hoses. No extra air is being introduced after the MAF (wouldn't want to confuse the ECU).

The breathers for the valve covers are now completely separated from the vaccum circuit (no longer under vaccum. Also, vaccum is good for the crankcase -> piston ring seal, but I can't see the real benefit of pulling air out of the valve covers as there are no components there that need to operate under even slight vaccum. Please let me know if I am wrong on this one). The routing for the single breather encompasses similar length hosing to the original factory setup, though it no longer connects in any way with the intake. I doubt much extra oil mist will be dispersed via this method as the breather's (sourced also from Summit) filtrating element is exactly like a K&N and those seem pretty good at keeping stuff containd (albeit out of the engine rather than in it).

I would venture to say this is actually a more efficient method when it comes to air/fuel ratios since the air evacuated from the crankcase and valve covers is not measured by the MAF and therefore not calculated into the fueling equation. In reality though it probably doesn't make one bit o' difference. The biggest gain is the oil mist removed from the intake tract, again better for you turbo guys. I've been drivin' it about a week now and if anything goes awry I'll let you know (don't think it will though)
Marshall Jung
92 Legacy 5MT (Home Depot Edition)
Legacy777
Site Admin
Site Admin
Posts: 27884
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Post by Legacy777 »

This setup has some issues, but how important they are......can't really say.

As for a/f ratios, it doesn't matter that the pcv system pulls vacuum from the crankcase. Where did that air come from? The intake manifold past the MAF sensor. The entire system is a closed loop system. What you've done is actually created an open system, it may not be a complete open system, but it's semi-open/closed, depending on how you look at it. Metered air is now being expelled to atmosphere.

Like I said, how much of an issue is this......I can't really tell you. In good practice you would want to run all the breather lines into the catch can. Then have a return line that goes to the PCV valve, and another that goes to the intake manifold.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
2020 Outback Limted XT

If you need to get a hold of me please email me rather then pm
ciper
Knowledgeable
Knowledgeable
Posts: 4388
Joined: Tue Oct 15, 2002 8:16 pm
Location: SFCA

Post by ciper »

SubaruCO: The valve cover "cavity" is connected to the crnk/oil pan cavity. The vacuum from the intake never depressurizes the crank because the valve covers are letting air into the system!! Which is also allowing air into the intake after the AFM.

How do you think oil in the valve cover area returns to the oil pan?!
SubaruCO
In Neutral
Posts: 23
Joined: Fri Apr 04, 2003 11:54 pm
Location: Denver, CO

Post by SubaruCO »

Ahh...good points. Well, nobody said building your own modifications would be simple, they are just cheaper. This is why this board is so useful. Replumbing the breather lines into the oil separator later today.
Marshall Jung
92 Legacy 5MT (Home Depot Edition)
SubaruCO
In Neutral
Posts: 23
Joined: Fri Apr 04, 2003 11:54 pm
Location: Denver, CO

Post by SubaruCO »

Just thought of something else. I can't exactly remember the routing of the original plumbing, but I think the valve cover hoses connected to the intake before the TB. Under closed throttle conditions when the PCV valve is active, would the engine be pulling fresh metered air through the valve covers and into the crankcase? Under open throttle the PCV is closed and the intake then pulls oily air from the valve covers and thus crankcase. I don't know how much air could flow between the valve covers and the crankcase, after all it's an oil passage and I'd think less air would be better. Sure would like to catch the engineering principle behind this vaccum circuit. Anybody like to take a stab at it?
Marshall Jung
92 Legacy 5MT (Home Depot Edition)
Legacy777
Site Admin
Site Admin
Posts: 27884
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Post by Legacy777 »

I'll try and scan the PCV diagrams this evening.

Remind me.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
2020 Outback Limted XT

If you need to get a hold of me please email me rather then pm
ciper
Knowledgeable
Knowledgeable
Posts: 4388
Joined: Tue Oct 15, 2002 8:16 pm
Location: SFCA

Post by ciper »

SubaruCO: Good catch!

I think its that way to help take oil from pooling in the valve covers, the oil will block the channels first so it would act almost like an air pump
Legacy777
Site Admin
Site Admin
Posts: 27884
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Post by Legacy777 »

Here's the diagram
http://www.main.experiencetherave.com:8 ... system.jpg

It sounds like the valve cover openings are used to feed fresh air into the system when the PCV is open under strong vacuum. But under low vacuum, blow by gasses could probably escape through them.
Last edited by Legacy777 on Thu Aug 21, 2003 4:50 am, edited 1 time in total.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
2020 Outback Limted XT

If you need to get a hold of me please email me rather then pm
SubaruCO
In Neutral
Posts: 23
Joined: Fri Apr 04, 2003 11:54 pm
Location: Denver, CO

Post by SubaruCO »

Thank you for the scanned diagram. Low vaccum probably explains the oil in the hoses. I guess other than introducing a lean condition (the extent of which is probably pretty minor, though still existant) the breather setup should not cause too many probs. I'll plumb it back to the intake just to be sure. Intersting...looking at the diagram, the second hose connected to the intake (moving left to right) t's into the PCV line from the crankcase. I'd think the draw under high vaccum would follow the path of least resistance, which seems like pulling from the intake, defeating the line from the crankcase. I'd say the ideal setup would eliminate this second line and placing an oil separator in line with the PCV, leaving the valve covers stock. Thanks again.
Marshall Jung
92 Legacy 5MT (Home Depot Edition)
Brat4by4
Stratified
Posts: 1608
Joined: Thu Jan 30, 2003 6:52 am
Location: NE Ohio

Post by Brat4by4 »

I snapped to attention when I saw that oil blow-by could reduce intercooler effeciency. I have my AWIC sitting in my room right now. What could I use to clean accumulated oil deposits off of the inner core of the intercooler? What removes oil well? Rubbing alcohol, gasoline, turpentine, aircraft paint remover, benzene, hydrochloric acid? :twisted:
1993 WMP BC6 5MT EJ22T 9psi 3.9:1 213k 205/55R16

62.6 m/s @ 0.66 bar. Gotta love boost. :)
eastbaysubaru
Knowledgeable
Knowledgeable
Posts: 1312
Joined: Wed Oct 16, 2002 10:44 pm
Location: Northern Sonoma County
Contact:

Post by eastbaysubaru »

I'm not too sure, but 91% rubbing alcohol removes most anything. It works especially well at cleaning "glassware" :lol: I'm not sure if you'd want to put that in the intercooler though. Someone else may have a better idea.

-Brian
'04 PSM FXT
vrg3
Vikash
Posts: 12517
Joined: Sun Nov 03, 2002 2:13 am
Location: USA, OH, Cleveland (sometimes visiting DC though)
Contact:

Post by vrg3 »

I would think kerosene or diesel fuel would do a good job of cleaning it out.
"Just reading vrg3's convoluted, information-packed posts made me feel better all over again." -- subyluvr2212
Legacy777
Site Admin
Site Admin
Posts: 27884
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Post by Legacy777 »

pine sol
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
2020 Outback Limted XT

If you need to get a hold of me please email me rather then pm
Post Reply