Originally Posted by
petrified.rabbit
"sounds like" the pcv system.
the sludge is basically formed from (lets not get too technical here there are a lot of reasons) but the engine spinning and the pistons going up and down and blow by of the rings... this plus the heat of the engine "vaporizes" some of the oil..
now in the old days this sludge would just build up in the engine, and hopefully be drained with the oil. And then the pressure was realized and the blocks were vented into the atmosphere. NOW emissions kicks in and what to run those vapors back through the intake so you burn them before the are released. The reason it goes into your valve cover is because in your car the design allows the engine to act (is some way) as its own catch can. So the "solids" can go back into the engine versus coating your intake, etc.
The sludge build up is from the cool down process after the engine runs, and those passages do not get hot enough for the sludge to revaporize but it does get warm enough for it to bake and become a more solid coating.