The intake manifold gaskets on your 1999 Chevrolet Blazer are vital for the reliable operation of the engine. These gaskets serve as a buffer between the air, fuel, oil and coolant that all pass through or near the intake manifold. A leaking gasket will cause poor fuel economy, coolant loss and rough idle, and could eventually lead to failure of the 4.3L engine. The Blazer has upper and lower gaskets. The upper gasket provides a seal between the upper intake plenum and the lower manifold. The lower gaskets seal the lower manifold to the top of the engine head.
Remove the intake manifold. Do not remove the intake manifold as a single assembly; remove the upper intake plenum and lower intake manifold separately.
Cover the lifter valley, head openings to the crankcase, the EGR valve, left valve cover, distributor hole, intake ports and any other exposed openings in the engine with protective material.
Clean all of the dirt, grime and other foreign material from the lower intake manifold, upper intake plenum and the top of the engine thoroughly.
Remove the old gaskets using a gasket remover or razor blade. Be sure to remove every bit of gasket and sealant. Any particle, regardless of size, that remains when the new gaskets are installed will hinder their sealing ability. Be careful with the plenum, as this part is made of a polycarbonate plastic.
Lay a thin bead of room-temperature vulcanizing silicone compound at the front and rear edges of the head where the new lower intake gaskets will be installed. Extend it about a half-inch beyond the end of the edges onto the head.
Install the new lower intake gaskets. Two small alignment protrusions on the gaskets fit into two divots on the rear of the engine. Take your time and place the gaskets correctly, but keep in mind the silicone compound will become tacky. For this reason, when laying the gaskets, minimize movement after it is laid on the silicone compound.
Place the lower intake manifold on the top of the engine and reinstall the eight manifold bolts. Do not slide the manifold at all lest you damage the new gasket. The 1999 Blazer manifold bolts require a three-pass torque. Torque all bolts to 22 inch-pounds, then 106 inch-pounds, and finally 26 foot-pounds. This allows for an even torque and seating of the gasket.
Install the new upper manifold gasket on the lower intake manifold.
Reassemble the intake manifold and reinstall removed components and assemblies.
