Adding oil to my daughters truck this evening, found this in the oil fill neck. I checked the oil first, and it did not appear milky at all. This stuff is thick, like butter. This motor was just recently rebuilt from the bottom up.

 

here in Illinois in the winter you get condensation built up in the engine if you don't get the engine up to full operating temp.
short quick runs in the cold cause that stuff to build up.

it could also be small amounts of coolant leaking somewhere into the oil

 

The crank case has moisture in it.
At certain temperatures and pressure the moisture mixes with the contaminants and .,.. condenses... on the coolest surfaces which is the oil fill cap, valve covers areas.
Run the engine to full operating temperature long enough to evacuate the crankcase through the PCV valve and hose.
The crank case is fed filtered outside air from the intake system but operating temperatures are the key to keeping this under control.
Good luck.

 

Thanks for the information. Helps out a lot.