If this is a common problem (and it is for us), I would expect more people to chime in on it.

I noticed that the 4G52, 4G54 and 4G63 engines use an "oil separator. What is its function?

The truck we are working on now has a 4G52 with 5500 hours and has the same compression as a new engine. The is a small hose that goes from the valve cover to the governor. When we disconnect the hose the engine stops smoking. Any ideas.