One test is to run the engine and look for bubbles in the radiator reservoir. That means a leaking head gasket.
Another is to pull the plugs and ensure they all look just alike and are carboned up. Any nice and shiny means water.
I learned the hard way about yellow oil on a boat engine. Yours doesn't seem to be that much milk.
Remove the oil fill cap and look on the bottom side of it and on the walls of the fill pipe. If you see white goo and you pass the other tests, probably just condensation.
Best way to stop that is to put cardboard in front of the radiator and run the engine till it warms up every time you start it in the winter. I do and never even go up the oil fill cap.