Oil at the top of the engine flows very slowly, You also will not see it come out of the top end right off the bat. It could take up to 5 minutes to start coming out depending on the engine and miles. Take the valve cover off and run it for a few and just keep an eye on it.

If the oil valve sticks..this can happen. Pull off the oil filter adapter and check that the pressure valve and it'* spring move freely.