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1996 Bonneville SSEi. Noticed lately that the coolant level in the overflow slowly keeps going down. No leaks underneath on the concrete. Opened the oil cap to find a slight orange/white colored condensation on the inside of the cap. None inside the valve cover that I could see and the none on the oil dipstick. Oil level is normal. Intake gasket? Head gasket? or something else?

Have the lower intake gaskets been changed to the metal design? If not, they could be leaking. Also check the coolant elbows in the tensioner. They tend to crack and leak. Mine used to leak onto the lower intake manifold, so they would never drip onto the ground and the coolant would steam off when the engine was running, so it took forever to track the leak down. Those are two really common spots for leaks.

Also, head gaskets on these motors rarely fail unless it's been severely overheated, so I doubt you have any issues there.

Given the gunk under the oil cap, there's a 98% chance that you lim gaskets are leaking. Replace them with aluminum framed ones.

Thanks guys! Now, I've done the non- supercharged intakes with the plastic plenum Upper/lower (both '97's), but with the supercharger, is it the lower gasket kit and a supercharger gasket kit? Also, considered the plastic elbow, (have replaced them too) but doesn't seem to be leaking.

Yes, you need the L67 LIM gaskets along with a blower gasket. Get aluminum coolant elbows.

Is there any step by step online to replace these gaskets? I think I could do it, but would feel better if I had something to go by.

markr wrote:Thanks guys! Now, I've done the non- supercharged intakes with the plastic plenum Upper/lower (both '97's), but with the supercharger, is it the lower gasket kit and a supercharger gasket kit? Also, considered the plastic elbow, (have replaced them too) but doesn't seem to be leaking.

Noticed today that the elbow is leaking! Must have gotten worse. However, the condensation in the oil cap has me worried.

Here's a guide to the intake gaskets. Your procedure will be almost the same, only you'll have the supercharger to remove instead of the upper intake manifold. I think you'll also need a special tool to remove the fuel rail, not sure if you can just zip tie it out of the way on the supercharged cars, but its a really straightforward job. Just take your time and bag and tag each bolt.
http://www.pontiacbonnevilleclub.com/fo ... c3591.html

I have had two '96's and two '97's....all requiring intake manifold gaskets. At what year did they figure this issue out and start making them more reliable?

Not till sometime this millennium.