Hi, I just did an intake plenum gasket job on a 1996 General Motors 3.1 L V6 because I had a lot of water in my oil. I did not drive it much when I saw it overheating. I took it apart to find one water hole gasket bad. Also, I found corrosion around that hole and others.
I drilled thru the corrosion with a 3/16 drill down to clean aluminum and flat bottomed the drilled hole with an end mill of same size. On one water hole, I had to drill about 5 holes side by side to remove all the corrosion. I washed the drilled holes out with acetone and pushed JB weld in each hole. Then I secured a scrap piece of quarter inch aluminum plate covered with a sheet of plastic over each JB welded area to force the epoxy into the holes. After letting them dry overnight, the JB weld was nice a smooth with very little cleanup needed. I actually had to do this with the water hole on each head too.
I made special gaskets for each of the water holes on the intake plenum. I cut an aluminum sheet 0.083 inches thick which is about 30 thousands of an inch thinner than the old gaskets which are 0.115 inch thick. Their shape matched the old gaskets at each end of the head. The water hole in this insert was egg shaped to fit a standard o-ring 0.136 inch thick and diameter of 1.875 inches. This metal insert holds the o-rings from being pushed outwards. A piece of standard electric house wire with diameter of 0.081 inch was shaped to fit inside the o-rings to prevent it from being pushed inwards. The metal inserts, o-rings, and copper wire ovals were cemented in place again using a metal scrap onto the intake plenum.
I did not want to use the factory gaskets for the water holes. The factory gasket for the air passage holes is fine. Just coat the old gaskets with silicone before putting it back together. I cut the old air passage gaskets off the heads with an aircraft snips as not to have to remove the push rods. These six input air hole gaskets were cleaned up of extra material including the alignment pins to provide six nice gaskets for the air passages. I cemented these gaskets onto the intake plenum in their proper spots with silicone sealer holding them against the aluminum with more aluminum scrap quarter inch plate. Doing this allowed the old gaskets to fit against the plenum surface as if it were in its final place on the engine.
When all is dry and cleaned up of extra silicone sealant, the plenum was put in place with fresh sealer. This special metal gasket for each water hole provided the same sealing for oil on each side of the plenum. Silicone seal on each side of it provides a good oil seal similar to the original gaskets. I did not even use a torque wrench to tighten the plenum bolts, just a quarter inch driver with six inch handle tightening them evenly until all bolts were not able to move easily. Maybe the best aftermarket gaskets will do the same job, but my gaskets are better for my 1996 Chevy Lumina GM 3.1 L engine. I have driven it about 1000 miles to find it works well. Please contact me at.....................................................................