text: Radium Air Oil Separator-Return (AOS-R) Kit, Subaru BRZ/Toyota 86 – JT MODS
  Radium Air Oil Separator-Return (AOS-R) Kit, Subaru BRZ/Toyota 86
  High-powered modified 4U-GSE and FA20A engines tend to generate excessive blow-by oil and gasses. In these cases, an ordinary small catch can may quickly fill with oil and not be adequate.
  Like the Radium Engineering Dual Oil Catch Kit the AOS (Air Oil Separator) kit is responsible for keeping blow-by oil and other pollutants out of the intake pipe, manifold, turbocharger, and intercooler during all engine loads.
  The main difference is that an AOS system returns what is collected back into the oil pan (as shown below) so there is no servicing required. The built-in heater keeps water from condensing in the AOS. And because water is more dense than oil, there is an integrated water trap found around the bottom perimeter of the can.