It isn't steam... it is oil/blowby vapors. (IIRC, you did not re-do the rings and such.)
Do you have a PCV valve in the other side, or a breather cap like this? If not, then this vapor will increase at cruise; a PCV valve will fix it for idle and light to moderate cruise; at WOT, a PCV valve will not correct this. A PCV valve will keep the crankcase cleaner and help to keep moisture out.
If you want to add a PCV valve, first see what a vacuum gauge shows that you have for vacuum level in the intake manifold at normal idle.
