98STS

It could be either but since it is a Northstar engine I would bet the head gasket. In either case the fix has to be done with the engine out of the car, If it is just the head gasket the bolt down system has to be changed because it is the bolts letting go in the block causing this known problem. I found a company in Toronto that has a great fix for this, he created it he is at expertengines.com. I use him because GM does not have a proven fix for this problem the inserts do not hold. He is on of the only ones who will even tackle a Northstar engine. Good luck with you engine because it is great once you can hold it together :)

it can be either of it. but more likely it is the blown gaskets.