I own a 2007 Ford Fiesta ST150, I have modified it a little, one of the mods is a cold air intake.

I want to install an oil catch can setup, but as the PCV vent is behind the intake manifold and requires the entire manifold to be removed to access it, I wanted to post my plan here first to make sure it will work before I pull anything apart.

My engine has two PCV valves. One is the upper crankcase breather, which routes back to the air intake. The other is the lower crankcase breather, which routes back into the intake manifold.

Here's a picture of the upper crankcase breather (actual photo of my car): enter image description here

The crankcase breather is circled in pink, and the point where it enters the intake is circled in green.

Here's a photo of the lower crankcase breather and the hole on the intake manifold that it leads to (not my pictures): enter image description here enter image description here

The important point is circled number 1.

Now you have the full picture of the PCV system on my car. Here's a drawing of what I plan to do: enter image description here

It's pretty easy to understand, but the idea is to route a tube from both the upper and lower breather vents into the oil catch can (either using a t-join, or by using a dual inlet catch can). Then, I have tube from the outlet of the catch can, to a t-join, which splits and leads to the CAIS and to the hole on the intake manifold.

My question is, are there any problems with this setup? Will it work? Is there anything I haven't thought about?

  • Maybe I'm misunderstanding the purpose of a catch can... but unless the upper hose is dumping oil onto your air filter or into your intake box, why don't you just leave that one as is and do bottom hose only?
    – Zshoulders
    Feb 16, 2017 at 19:33
  • I believe both hoses actually carry dirty air, they just go to different locations.
    – WeakMech
    Feb 16, 2017 at 21:07

1 Answer 1


I would assume, from inspection and not knowing your vehicle, that the upper and lower pcv's operate at different pressures (depressions really as below atmospheric) otherwise they would have had them joined together already...

  • Does that mean that they can't be routed to the same catch can? Or could I route them both to the catch can, but then seal off the hole in the intake manifold and have the outlet of the catch can leading only to the air intake?
    – WeakMech
    Feb 16, 2017 at 12:43
  • As they are separate systems then NO don't connect them together.
    – Solar Mike
    Feb 16, 2017 at 13:49
  • What if I used a catch can with 2 inlet ports? Still a no go?
    – WeakMech
    Feb 16, 2017 at 19:03
  • Or I could use two catch cans but that seems like overkill...
    – WeakMech
    Feb 16, 2017 at 22:26
  • A catch can with two inlet ports does the same as your Y connector... Two catch cans as the systems are separate : you could try one on the lower crankcase breather and see if that helps (if there is a problem). Then decide to add or not the upper one based on the results...
    – Solar Mike
    Feb 17, 2017 at 8:53

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