What is a PCV system?

The goal of a positive crankcase ventilation (PCV) system is to limit the amount of residual oil and vapor, that is released from the crankcase, from entering back into the throttle bodies inside the intake plenum. Overtime oil can build up around your throttle bodies, combustion chambers and idle control valve (ICV) valve which can lead to various performance issues such as rough idling.

Although most cars have some sort of PCV system, it’s still not enough. That’s evident when owners have to clean their throttle bodies and ICV valve. We made an article on how to clean that for this reason and you can check it out here: E46 M3 Throttle Body and ICV Cleaning DIY.

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E46 M3 Throttle Body and ICV Cleaning
E46 M3 Throttle Body and ICV Cleaning

So how does the oil catch can make a difference?

The oil catch can simply routes the residual oil and vapor from the crankcase into an isolated container opposed to routing it back to the intake plenum.

If you ever remove your intake plenum, you’ll notice the small oil vent line connected underneath. This routes back to the oil pan. But think about it, you’re really trying to force the vapor and oil from the crankcase, through the breather tube, into the plenum, somehow bypasses the intake trumpets, and seeps downwards into the small hole? Why not just stop it from entering the plenum in the first place? That’s the idea of the oil/air separator AKA catch can.

E46 M3 Throttle Body and ICV Cleaning
E46 M3 Throttle Body and ICV Cleaning

Is the catch can worth it?

Regardless of your usage, by the book the answer is always yes. You don’t want to recirculate dirty oil and vapors back into the plenum. Check out the video of how much stuff came out. This is the results after maybe 4 track days.

The Moroso setup

There are several catch cans out there, but I chose the Moroso simply because of engine bay aesthetics. I have a matching Moroso Expansion Tank for the coolant and the generic catch can they sell perfectly mounts into my existing air pump bracket. It’s like it was meant to be!

Moroso Oil Catch Can and Expansion Tank Review - E46 M3

Moroso Universal Air/Oil Separator

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Moroso Expansion Tank

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Moroso Oil Catch Can and Expansion Tank Review - E46 M3
Moroso Oil Catch Can and Expansion Tank Review - E46 M3
Moroso Oil Catch Can and Expansion Tank Review - E46 M3