DIY: Dual Oil Catch Cans 370Z

Originally Posted by wstar

Don't recirculate the catch can fluids back to the oil pan, it's a bad idea. It's not just oil trapped in them, it's also blowby gas and other vaporized crankcase gasses, which means it's got a high amount of both raw fuel and combustion byproducts (carbon, etc) blended into it. Just smell it once when you're dumping the cans and you'll smell the fuel in it (and as noted above, it picks up a bit of water vapor too).

(Also: you'd be creating a vacuum leak and/or another PCV flow path if you hooked up open drains back to the oilpan, too).