I just want to bang my head against a brick wall!!

My last few threads were about the sub-frame mounts rotting, I did get that all buttoned up and everything is good there now.

BUT my Dad just called me (mind you, the car has sat for a few weeks at a time). The last he drove the car it was sputtering. We figured bad gas from sitting.

Nope!! The upper intake gasket is leaking coolant now... just our luck.

How difficult is it to replace the upper intake gasket?

I can do it in 40 minutes from start to finish. unbolt the throttle body from the bottom and upper bracket, remove the fuel rail with the injectors still on it and set it off to the side, and unbolt the plenum.

If its leaking though, it could be a warped plenum if you have the plastic one. It happened on my L27 and I've heard it happen to other people. Your options are to replace it with an aluminum plenum from a junkyard, replace the gasket and hope for the best (didn't work for me), or tap two threads into throttle body coolant passages and screw in some headless bolts to plug them up. You can get them from any hardware store, and they permanently fix your coolant leak.

Here are the holes you would need to plug up:



You would use a pipe plug bolt, which looks like this:

Could this also be a bad LIM gasket? We know the LIM'* had the same issues as the Series II gaskets... but most never pulled LIM'* to find out.

I changed my 92 SSE L27 LIM at 150K. It looked pretty "wormy" on the sealing surfaces or on the edge of leaking. If you are going to do the UIM, I'd take the deep dive and do both so you won't shoot yourself when the LIM takes a dump. I have 250K on the engine now.

Do a search and you'll find all the precautions about draining contaminated oil that will affect the rod & main bearing and such when a manifold gasket leaks coolant into the engine.

I say go one step deeper and do the LIM gaskets as well. Adds about $50 and about another hour or so.

It isn't that hard in my opinon. You can buy the shop manuals on ebay for next to nothing compared to what I paid for them 14 years ago, $94. The torque specs are extremely low. In all probability your upper and lower manifolds are warped. If you have to be able to drive the car, go to the junk yard and buy a set. Depending on where you go they are anywhere form $45 to $90 for the set. Find a good machine shop and have them resurfaced, not milled. Milling will take off took much stock and the lower manifold won't sit on the heads properly. Be sure and use the FelPro neopreme (sp?) gaskets. The hardest part will be on your back bending over the fenders unless you can put it on a lift.

I love my Bonne, bought a 92 new Thanksgiving '91 and it still runs great with 255k miles, original engine (valve job & timing chain), transmission & cv joints. What a car! Too bad GM quit making it. GM was too cheap to spend money on it, but not too cheap to pay themselves too much.

Good luck with your project! Let us know how you do.

Where does one find the aluminum plenum? On which vehicle?