Originally Posted by JCL

It is not the crankcase vent valve, also known as the oil separator. It is due to condensation in the engine, which emulsifies with the oil. It is the result of doing lots of short trips where the engine doesn't get hot enough. If the engine does get hot enough, the condensation boils off. If it doesn't, it collects over time, often under the oil filler cap.

Now here is the connection to the CCV, or OSV: the condensate can collect in the crankcase vent valve, and clog it up. If it gets cold enough, the condensate can freeze, blocking the valve. That is when you get problems. The CCV is not the cause, it is where the symptoms can occur. Since it is so often mentioned in conjunction with this problem, people assume that the CCV is the cause.

The cure is to do a few hot oil changes in short order, and ensure that your driving includes a few longer trips that keep it at bay. You may want to get the CCV checked and cleaned out if you live in an area where it gets significantly below freezing, to manage the risk of a failure there. If you don't live in a very cold area, there is limited risk.