View Full Version : Why Leaking Headgaskets

09-17-13, 09:11 AM
My allante 1993 built Aug 1992 - bought by me 1999
with 65,000 miles.
Antifreeze green and goodlooking . don't know how old,

Have had waterpump lubrication and anticorrosion - Prestone
or Union Carbide or STP - these are what I use and they look
the same like milk.

2010 or 2011 I changed antifreeze to DexCool and with STP
waterpump lubrication and anticorrosion at 90,000 miles

At +100,000 miles nov 2012 the Engine was taken out and
rebuilt exclusive the bottom part.

None trace of leak or leak tendency was found on HG gasket.
According to the rebuilder the leak starts around cylinder 1
or between 1 and 2.

Why har HG leaking - and why were mine like new though
antifreeze change was totally rejected?

Any ideas - is the Waterpump lubrication/anticorrosion the

bill buttermore
09-17-13, 01:19 PM
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.

09-17-13, 07:08 PM
I have time serts today - is this better than original new block?

09-17-13, 08:08 PM
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.

09-18-13, 11:05 AM
Clarify please?
Your motor was repaired using timeserts nov 2012
Motor has issues now?
Using coolant? Overheating?
Motor is in car now? Mechanic has not pulled heads to figure out what is wrong?

09-19-13, 06:54 AM
Enginge was pulled out because of the infamous N* oil leak in
the oil manifold - fixed by loctite sealer.

At the same time - heads were rebuilt with valve job and
one of the intake or exhaust guides (all these but the shortest)-

Head gasket had no trace of problems

The front and rear seals new +

new water pump, starter, Engine/tranny mounts/all, torque
converter and tranny including Electronics and TCC new.

Rebuilt rack & pinion and all Power steering hoses (made here
. better than oem)

I afterwards made polyurethan upper torque bar/Engine mount
bushings (very successful with basic body mount from Energy
Suspensions - which I turned in a lathe and grinded)

Why is the HG common on the rear bank Close to cylinder 1?

09-19-13, 07:35 AM
It's not common to any particular cylinder/s. Any one, or any combination of the head bolt holes can strip.

ANY TIME the heads are removed from a Northstar, the block MUST be inserted or studded. Did your mechanic not do either?

09-19-13, 10:03 AM
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.

09-21-13, 05:07 AM
As I wrote - bought the N* star Allante in 1999-
it was flooded in Florida - first registered N* allante
here in sweden.

bought it with 65,000 miles rebuild at slightly more than 100,000

At the rebuild Time Serts installed as I wrote - car is perfect now.

It is a handbuilt car like Ferrari - but with a relatively common but
expensive - but far from Ferrari - driveline

09-21-13, 08:19 AM
Oh, I see. You are just asking WHY headbolts fail? Your motor is fine