Usage:
3406 Truck Engines
New cylinder heads have additional coolant passages in the rear part of the head. The additional coolant passages provide improved coolant circulation in that area. This will result in reduced thermal stresses in the head to block joint at the rear of the engine. The reduced stress will result in increased cylinder head gasket life.
Initially, the cylinder heads were drilled to add two coolant passages. This change is identified by the pipe plug at the rear center of the cylinder head, between the head bolts. This change is in effect as listed in Chart A. The new cylinder heads are cast with the additional coolant passages. This change is identified by the casting part number 9Y3777 (not serviced) on the left rear side of the cylinder head. The new cylinders heads are in effect as listed in Chart B.
Chart C identifies the current and former new and remanufactured cylinder Head assmeblies and groups.
