Just joined, but I read the title, and I'm commenting based on the very first post/question as asked.
I'm sure many of my observations have been noted by others (and this thread is really long), but I'm simply trying to be helpful to those unfamiliar with, or that don't know or wonder why/where/what is going on with these engines. Again, not stepping on toes, just commenting based on my experience.
As a dealership Shop Foreman, I've been involved in over 200 NorthStar head gasket/block repairs since the late 90's-2011 (dealership), and at my independent shop we did over 40 this yr alone!
Head gasket failure in NorthStars' is rust related. Period.
...and, yes, 99.9% are DexCool engines.
That being said...IF you had head gasket failure on a 1993-95 NorthStar, it either had (1) exceptionally bad maintainence routines',(2) dexcool introduced at some point in its life (which dealerships were advised to use in ALL heater core failures in the late 90's!), (3) previous engine disassembly and repair early in life (wristpins were common failures), or (4) SEVERE overheating at some point. Most of them that are overheated that badly (to "blow" a h/g) will have a cracked aluminum liner casing as evidence. Early engines also dealt with block porosity, but not super common. Most of them broke bolt holes externally, seeped water, or cracked around rear main. I'm sure a few pulled bolts from porosity, but I never personally experienced it. Many more had wrist pin failures, which I suspect early service repairs may have resulted in thread pull later in life.
They fixed the porosity problem about the same time as oil consumption became an issue...but that's another story...
Funny thing.
1993-95 with head gasket leaks seem to push water ONLY on very long hwy drives...because the average cylinder pressure is higher at 2000rpm than low/varying engine speeds, I theorize.
96 up loose water over a set amount of time...which gets closer and closer and closer as the rotting continues to worsen. Also, most, if not all, will have an engine miss when cold, once the rusting has progressed sufficiently, early engines don't seem to have the same symptoms cold.
All of them seem to have something I call
"The Rule of 3's"
Water pump, pump housing seals, radiator...then HGs
Radiator, coolant reservoir, water pump...then HGs
Heater core, radiator, water pump...then HGs.
X, Y, Z...then HGs. Everyone seems to have already had a leaky X, Y, Z, then they finally figure out the pressurization of the cooling system is simply making things leak from abnormal pressures during warm-up. Think about it if you've had HG failure. You probably did 3 things before you diagnosed the HG failure...
These failures are TIME related...NOT mileage!
The bolt threads pull because they have to be removed. Many times we find dexcool in the bolt holes, usually those pull worse. No gasket failure, no coolant in threads, no bolt removal, no thread repairs...ect. We've ALREADY done several 04's, 05's, and (2) 06/07 DTS's...one of which had only 53K.
So no, the pitch of the threads had absolutely nothing to do with it.
I'm sure some of the experts here will disagree, but I can post up, literally, pics of 100+ head gaskets that I keep to show customers.
I call it the "Wall of Shame".
Just plain rust bubbles...from DexCool coolant.
We use only conventional green coolant and advise the customer what to use and why.
DexCool is not allowed in my shop.
Period.