+1 ^^^
Replace PCV Valve every 2 oil changes when miles get higher, 200k+, or clean it "real good", it can help keep moisture in upper engine down, it isn't coolant it is just moisture from the air that is pulled into the engine areas like valve covers
Check Overflow hose for leaks, and get rad cap tested or replace it.
As engine coolant warms up it expands, that is what creates the pressure in the system, when pressure gets to 14psi rad cap opens and sends coolant to overflow tank via overflow hose, and this is HOT coolant so will evaporate pretty quick, no visible leaks
After engine is shut down coolant cools down and shrinks, pressure in the system goes down until it gets to -1psi, then the smaller valve in rad cap opens and SUCKS coolant from overflow tank via overflow hose, back into the radiator.
So when you open rad cap on cold engine it should be full to the top, no air at all
This is a self purging system