Sometime you might open up an oil filler cap and you will see abnormal small deposits(emulsions) there. It often happens when we drive a cold engine during the winter time. Eventually, moisture that starts to get into the engine turns oil into light-beige emulsion.
When you are seeing dark-brown tarry deposits - this indicates a severe contamination of the engine oil system.
Change the oil and clean the oil system: VitaFlush – oil system cleaner need to be applied right after oil change(245-620 miles of run).
If such an occurrence is observed in winter and the problem disappears after the engine is warmed up, there is nothing to worry about, it is a normal process.