A. Coolant loss on 1992-1997 4.3L GM VIN R & W engines has been, at times, difficult to detect. The cause of the coolant loss has been traced to cracks that may develop in the lifter valley area of the block and allow coolant to pass into the valley of the block. This loss of coolant can lead to engine overheating or contamination of the engine lubricating oil supply or both.
While these cracks are not always visible to the naked eye, they can be readily identified through the use of standard crack detection equipment. These cracks may be repaired by various methods. Evaluating the severity and length of all cracks before other machining processes may prove cost effective. In most cases, extensively cracked blocks should be discarded.
Q. An installer complained that his rebuilt 8.1L GM engine burned a lot of oil. What could be the cause?
A. Engines use various amounts of oil depending upon the severity of use and load. One quart or more per 100 gallons of fuel is generally considered too much.
It has been determined that oil vapor can enter the intake manifold of 2001-2002 8.1L GM VIN G engines due to an insufficient intake gasket applied load. To resolve this condition, new service intake manifold bolts have been developed (p/n 12561518). Ten are required to fix the problem. Torque has also increased according to the installation procedure.
- In the order of sequence shown in Figure 2, above, loosen and replace one bolt at a time. Insert a new bolt and torque it immediately to 44 in.lbs (5Nm).
- After all ten bolts have been replaced with new bolts tighten each bolt in sequence to 71 in.lbs (12 Nm).
- Tighten all bolts in sequence to a final torque of 106 in.lbs (12 Nm).
This procedure should also be used any time the intake manifold gaskets are being replaced. Older service manuals should be updated with this current information.
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