With a tool called a slack tube manometer.
In crankcase filter box
...It will be what ever your suction pressure is.
Excessive crankcase pressure can be caused by several factors, including worn or damaged piston rings, which allow combustion gases to escape into the crankcase. Blocked or malfunctioning positive crankcase ventilation (PCV) systems can also lead to pressure buildup. Additionally, oil leaks and excessive oil levels can contribute to increased pressure. Overheating or engine wear can exacerbate these issues, leading to further complications.
combustion pressure will leak into the crankcase, and oil from the crankcase will leak into the cylinder.
1. The crankcase breather may be plugged. or---- 2. Too much crankcase pressure. There is too much blowby (combustion gasses leaking by the rings or piston), causing excessive pressure in the crankcase. To repair this, you will need to re-ring or bore out the engine with new pistons and rings.
The PCV or positive crankcase ventlation valve does as it is named. It will remove harmful gases from the engine. Also, you can find breather caps on the valve covers, this also helps to remove and fumes from the crankcase or engine base.
If the rings are completely worn out they can put more preasure in the crankcase than the pcv can handle. Have it checked out.
split open the crankcase
There is not a pressure switch however there is a temp warning sensor on the back of the crankcase in the bottom
Vacuum should always be present in crankcase, it is provided by the PCV (positive crankcase ventilation system) pressure is what you don't want to see.
Did you mean PCV [positive crankcase ventilation]....that valve helps keep engine gasses from going to the atmosphere but wont allow intake pressure back to the crankcase.
Chech the pcv valve. The oil is due to excess crankcase pressure.