There should not be a vacuum in the crankcase. The crankcase ventilation system has an orifice built into the intake manifold. The orifice uses intake vacuum to draw crankcase vapors into the engine air intake. The engine then burns these vapors.
In order for the system to work there has to be a clean air intake into the crankcase. I went and looked at my 8.1L engine but can't see where filtered air is introduced into crankcase. Maybe someone else can enlighten us.
If you have a vacuum in the crankcase it indicates that the intake air is plugged.
2003 34' Georgetown on W20 Workhorse Chassis. UltraRV power mods. Doug Thorley Headers and MagnaFlow 12589 mufflers. Front Sumo Springs, Rear P32 Sumo Springs, UltraRV Track Bar.
1998 Jeep Toad.