CRANKCASE VENTILATION
1986 CRANKCASE VENTILATION Mercedes-Benz
DESCRIPTION & OPERATION

NOTE: Information on 300 series not available.
DIESEL MODELS
190D

The system consists of an oil separator located under valve cover, distribution tube on intake manifold, and return flow tube. California models are equipped with a diaphragm regulating valve located in the oil separator.

When the engine is running, blow-by gases flow through the oil separator, through a connecting hose, and to the distribution tube on the intake manifold. Oil from the separator returns to the cylinder head through the return flow tube.

On California models, the diaphragm regulating valve is used to prevent excessive vacuum from forming in crankcase.

Fig. 1: Crankcase Ventilation System (190D) Federal models do not use a diaphragm regulating valve.
GASOLINE MODELS
190E 2.3

The system consists of an oil separator located in the valve cover, idle speed air distributor, and a connecting hose.

When the engine is operating under high intake manifold vacuum, blow-by gases flow out of the valve cover, through the by-pass bore in the idle speed air distributor, and into the intake manifold idle speed air passage. A small amount of filtered air is drawn into system through the by-pass hole.

When the engine is operating at low or no intake manifold vacuum, blow-by gases flow into the air cleaner where they are mixed with filtered air before burning.

Fig. 2: Crankcase Ventilation System (190E 2.3)
190E 2.3-16

The system consists of an oil separator located in the valve cover, idle speed air distributor, idle speed air line, coolant lines and connecting hoses.

When the engine is operating under high intake manifold vacuum, blow-by gases flow out of the valve cover, through the by-pass bore in the idle speed air distributor, and into the intake manifold idle speed air passage. A small amount of filtered air is drawn into system through the by-pass hole.

When the engine is operating at low or no intake manifold vacuum, blow-by gases flow into the air cleaner where they are mixed with filtered air before burning.

To ensure against vent line freezing, coolant is routed to vent line from cylinder head. Coolant returns to water pump through coolant return line. See Fig. 3 .

Fig. 3: Crankcase Ventilation System (190E 2.3-16)
All Other Gasoline Models

The system consists of a fresh air hose from air cleaner to right cylinder head cover, a breather hose from left cylinder head cover, an orifice, and a connection to intake system.

During idle or low speed operation, vapors are drawn through the orifice, into the idle air distribution tubes, then into the intake manifold. Fresh air to vent the engine comes through the air cleaner and right cylinder head cover hose. During high speed operation the vapors are drawn in through the air cleaner and burned.

Fig. 4: Crankcase Ventilation System (420 SEL - Gasoline Shown; 500 Series Similar)
TESTING

NOTE: Testing information not available.
MAINTENANCE

The crankcase ventilation system is maintenance free, but hoses should be checked to ensure that they are not cracked and are free of obstructions.

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