I overfilled my oil system once and my exhaust blew smoke out for a while. I had to drive hard to burn off that oil during my road trip. It cleared up around somewhere in Arizona, after I left from San Diego.
I think it might be the gasket also, but check your cap and see if there is an O-ring around it. I'm not sure, but I think there should be one there to help seal and keep the cap from leaking.
