Here's my understanding of the AVCS engine breather/PCV arrangement......


All the early turbo and NA engines pre-avcs use the same PCV system that fundamentally requires low resistance air flow through the oil return ports in the bottom of the heads.

Add AVCS and now this is a bit more difficult due to the increased oil congestion in the heads (spray from the avcs solenoids) - so Subaru had to allow for an alternate low restriction air flow path between the heads & crankcase...... That path being the larger of the 2 fittings on the heads & the one on the crankcase....Hence no baffles.

Originally on your engine there were three ports directly plumbed into the three main oil sections of the engine (the larger of the two ports on each head run to the central crankcase fitting). <- You need these, they ARE NOT PCV lines!

There isn't supposed to be any oil separation occurring on those lines, they are there simply to allow the blow by gases to equalize between the heads & the crankcase. They don't vent externally either via the PCV or back to the intake on the OEM set up. These are completely separated from the positive crankcase ventilation system.

They are the top lines in this diagram (the 2 head breathers feed into the central crankcase fitting):




Now the actual PCV system!

The PCV to manifold hose is supposed to feed off the fitting (actually the PCV valve is housed inside here too) in the rear of the block (driver's side) as your specific block has the oil air separator built into it & the PCV is attached to the separators outlet.

(Item 4 is the oil air separator cover in the image below)



The Pcv is here (inside the rubber section below the square based fitting):



This is the actual PCV assembley (P/n:11815AB790) and what it looks like! :
(This is the OEM Subaru 2005-2006 Legacy GT PCV Valve & Hose Assembly.)



Is this the fitting that your not currently using?........It's the root of all evil on the Legacy forums (they are prone to freezing open)!

This system is totally Unlike the non AVCS pcv system that has a pcv valve screwed directly into the inlet manifold.

I'm not sure if I've explained it very well but I'd be happy to clarify anything as needed.


Rossco - never sleeps!

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