GM 6.5L V8 – Cylinder Case and Head Passages

The path of coolant moving from the water pump includes cylinder case passages surrounding each of the cylinder bores and cylinder head passages surrounding the combustion chamber and valve port areas. Each cylinder head gasket has restrictions to control the flow of coolant from the cylinder case into the cylinder head passages.

Cup plugs seal five of the six cooling system passage openings in the cylinder case (see Figure 4-4). The sixth passage opening has a special plug with an integral heating element that is used for warming the engine for starting in extremely cold temperatures (see page 8-2 for more information).

Each cylinder head has a plate retained with bolts and a gasket to seal a rear cooling system passage (see Figure 4-5, view A). The right cylinder head has a threaded plug at its outer rear corner to seal cooling system passages. Both cylinder heads also have four small cup plugs beneath the intake ports.

The left cylinder head uses a switch (for an engine temperature warning lamp circuit) or sending unit (for a gauge circuit) threaded into the outer front corner location (see Figure 4-5, view B). The engine temperature warning lamp will light when the cooling system temperature at the left cylinder head switch location is above 258° F (126° C) (see page 8-36 for more information).

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