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OT Help with 98 STS Cadillac
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Post OT Help with 98 STS Cadillac 
Hey guys. I need some help with my Dad's 1998 STS Cadillac with the 4.6L Northstar engine.
It has been drinking a lot of coolant. I cant see it leaking, and the dipstick doesnt show a level increase.
Its got about 100,000 miles on it.

I am guessing an intake gasket. I just wanted to run this by you guys.

Thankyou in advance.


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Post Water Pump? 
On my Mom's 1995 STS, it drank coolant for 6 months before you could tell that it was the water pump.

These engines aren't really pre-disposed to the intake manifold gasket problems like the L31 and the 60 degree V-6's of the late 90's early 00's. Not saying it's impossible, just relatively rare.

You've pretty much eliminated head gasket.

Special tool required if it is the water pump.

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I think you nailed it, seeing as coolant can only go into the oil, into the combustion chamber or onto the ground. I wouldn't wait to fix it. Those engines are all aluminum, and that coolant will eat it out pretty quickly causing a much more expensive repair.

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Parents 91 STS is now my daily and it 'was' eating
coolant and milk shake on the oil filler cap. 4.9L
and not Northstar, though am told has similar/same

Solved it with band aids, but the issue is still there.

The block is two piece (don't know where the part
line is, but guessing horizontally, as vertically would
be crazy) with wet steel liners. That is the issue
am told, the liners.

Speed shop buddy said to go away, as he'll not
touch any of these 'crappy' blocks. Great when
the run, but at about 70K-80K miles, they have
heating issues, which turns into coolant issues
in the oil.

Another buddy who just retired, used to be the
parts manager of a large Caddy dealership and
confirms that around 70K-80K miles, they start
to come in with this symptom. If they don't have
the 'procedure' done, back with a blown engine
in less than 10K miles later.

One key thing is coolant flush, or not doing it
often enough. Seems it gets hot spots in there
and pings, which leads to compromising the liner.
Usually at the head/block area.

Dealers have a GM additive package for the coolant,
but must be installed before much damage is done.
Complete flush & cleaning, then water and this stuff.
then drain and fill with 50/50 coolant.

I've managed to keep this running without that
coolant additive (am told a few hundred bucks
just for the can, plus labor)....and....has to be done
early, and ours is too 'late' for this procedure...

Put in a 180*F thermostat with a 5/32" dia hole
drilled in the flange. Maybe a 170*F if they make
one in a 54mm dia config.

Back off the radiator cap so that it seals the over
flow route, but doesn't get full pressure for the
cooling system. Actually cut a slit in the lower
gasket so that the cooling system won't go much
above ambient pressure.

Added a new fan switch and is in line with the
hot hose from engine 'to' radiator. Relay has hot
lead directly from alt and fused at 30amp. Coil
hot lead is from the ACC on fuse block, so only
when ignition is on, will this circuit power the
fans (two of them, one pusher, other puller).

Runs well and strong, but if the rev's get over
3K, starts to consume coolant. No more milk
shake in the oil filler cap. Still smokes both front
tires off the line and in 2nd, but know that it
will then need coolant.

If it gets hot (over 210*F) it will ping on light
throttle and consume coolant.

Like this car, haven't decided to keep or sell,
but mom'n dad has conniption fits on that topic,
so keep it for now on limited budget (and too
many vehicles, for now). Really need a mini
van for them and their wheel chairs.

Asked this before and some one said southern
CA has some sand rails using these engines
and wonder if their engine builder know some
thing the guys up in northern CA don't????

PS...bought a water pump (life time, NAPA)
but then looked and holy crap, the whole
side (front of the engine) has to be removed !!!
It's still in the box...

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