Positive Crankcase Ventilation: Description and Operation

Heated Oil/Air Separator - "L & N" - 2.3(A,D,3):

PURPOSE
A crankcase ventilation system is used to provide scavenging of crankcase vapors. Blow-by gases are passed through a crankcase ventilation oil/air separator into the intake manifold. Incorporated in the crankcase ventilation system is a crankcase ventilation heater assembly. The assembly contains a heater (item #165) which is a positive temperature coefficient device. The purpose of the heater is to prevent icing in the crankcase ventilation system.

OPERATION
The only flow through the oil/air separator is the combustion blow-by, as there is no fresh air inlet to the crankcase. The image illustrates the system and identifies by number the components of the system. The primary flow of blow-by into the separator is through a hose (item #171) from the timing chain housing. The oil/air separator causes oil, which may be suspended in the blow-by gases, to be separated and drain back to the crankcase through a hose (item #167) to the oil Fill tube. This hose may also flow some of the blow-by gases into the separator under certain conditions. The upper smaller nipple connects through a hose (item #165) to manifold vacuum. The heater assembly inside the hose warms when the ignition is turned "ON" in order to prevent icing. This hose draws the gases from the separator under high manifold vacuum (idle or steady speed) conditions. There is a 1.52 mm (.060") orifice inside the smaller nipple to restrict flow through the hose (item #165). The lower, larger nipple, connects through a hose (item #168), to the air intake duct from the air cleaner. This hose draws gases & from the separator primarily under high air flow (high rpm), low vacuum conditions.