Northstar Engines and System Technical Discussion Discussion, Why Leaking Headgaskets in Cadillac Engine Technical Discussion; My allante 1993 built Aug 1992 - bought by me 1999
with 65,000 miles.
Antifreeze green and goodlooking . don't ...
Assuming your Allante has the Northstar engine, the reason the headgasket leaks is typically due to a loss of equal clamping force between the cylinder head and the engine block. Each time the engine comes to operating temperature, significant differential expansion occurs between the cylinder head bolts and the engine block. The powerful force of thermal expansion pulls on each head bolt. As the engine cools, this pulling force is reduced. After many cycles, some of the bolts begin to loosen, releasing the clamping force on the head gasket that creates the seal between the cylinder head and the block, and a headgasket leak occurs with no fault in the gasket itself. The Northstar was designed with each head bolt secured in the aluminum engine block with rather small, fine threads. The fix for this problem is to enlarge the surface area of the threads that hold the head bolts into the block preventing the bolts from losing clamping force on the cylinder head. There are two excellent methods for accomplishing this, both of which you can research in this performance section of the Cadillac Forum. One is to install studs with much larger threads than the original bolts, and the other is to install steel inserts with much larger threads bearing on the aluminum of the engine block. Both methods require enlarging the head bolt holes in the engine block and cutting new larger threads that provide a much larger surface area of aluminum to properly secure the head bolts.
The problem has nothing to do with "loose" bolts or unequal pressure. As posted, the head bolts in the early Northstars are too short, and use a fine thread. The bolt hole threads in the block strip out, leaving NO clamping force to allow the HGs to seal.
Using the new, larger TimeSerts, Norms Serts, or studs, gets you a long, coarse thread into the block, which should be a permanant repair.
So block threads were left untouched. And all headbolts torqued fine? And you used new headbolts? Sounds like you changed just about everything under hood. Must really like car. Or it was a disaster when u got it? Must have Been real cheap to buy. Since it had so many issues.