need advice white scum

moisture will boil out or get sucked when it gets warm. If your afraid to run a PCV due to mixture issues, run an evac tube from a header collector. Its just a pitot tube cut at an angle in the exhaust stream. Itll pull plenty of vacuum. some have a one way valve to prevent backfire pressures. Run a pressure test into your radiator, if it loses pressure over a few minutes, start looking..