Milky substance on my oil cap

V8Nissan

When you drain the oil, I would let the engine sit at least overnight and then not start it before draining it. See if the water / coolant separates to the bottom. Blackstone oil analysis is also an option if you can get a sample container quick enough or use another clean container for the oil until you can get one. They would be able to tell you exactly what it is most likely.