This whole headgasket problem with the Northstar engine has really piqued my curiousity. There's probably two different reasons for that - one is that I just purchased a '99 STS with 86k, and I'd rather not have to pull the heads, and the other is that I've had quite a bit of experience with Porsche 911's, which had similar headstud pulling/breaking issues (which, for obvious reasons, were not related to coolant changes or head gasket problems).
My question is basically whether there are two problems cropping up - headstuds have a tendency to pull out of the block and headgaskets are deteriorating when the coolant isn't properly maintained, or whether these problems are intimately related somehow (and not independent of each other).
The Porsche angle comes from the late '70s versions of the 911, which were basically magnesium blocked engines with aluminum heads. The headstuds (made of steel) tended to pull themselves out of the block due to the dramatically different thermal expansion rates of the two metals. The problem was exacerbated by the tendency of the engines to run very hot, due to the massive amounts of early emission-reduction "technology" on the engine. The solution was (suprise!) to replace the head studs and timesert the block. The problem was permanently cured in the 911SC, when Porsche went to a full aluminum block with aluminum heads. As such, I'm a little surprised to see a similar problem popping up in the Northstars, and the cause being attributed to the aluminum block. It sounds to me like the problem is really a design flaw, in that the engineers didn't properly account for the strength needed to keep the heads on the engine and the studs in their place, and not an inherent weakness in the use of aluminum in teh construction of an engine block. There are a lot of aluminum engines out there that do not exhibit these problems.
Lastly, I noticed that there has been some allegations as to poor quality headgaskets being used in a few years of the Northstar construction, and that also sounds like a pretty reasonable explanation for the headgasket deterioration. Regular coolant changes are certainly necessary for the longevity of any engine, but if there are problems popping up in cars with under 75k miles, when the coolant is rated for 100k miles between changes, I can't help but think there may be something more to the problem than old coolant. I'd love to have access to the data on these headgasket failures, and see how many occurred on cars without perfect maintenance of the coolant system compared to cars that were maintained properly.
Anyway, these are just some observations I've made as a newcomer to this forum and Cadillac ownership in general.