Get a flashlight and look inside the oil cap area. You need to see past the baffle and should see the top of the head. If it is has no sludge on it, you are good to go. Do not mind the baffle as it will always have some sludge on it. It cools down first and the oil vapor seams to condensen to it giving it a sludgy appearance.
After dealing with what i delt with, I am a firm believer of SeaFoam. If you see any sludge- Seafoam it.
Before changing the oil, pour an entire container of SeaFoam into the crankcase. Depending on the severity of the sludge, drive around about 20 minutes. If you see your oil pressure light flicker on or your oil pressure gauge read low, stop and change your oil.
After the initial flush, add new oil and then poor another container of SeaFoam to the crankcase oil. Then change the oil at the normal oil change interval.