I've read a lot of differant stuff on this site and I'm get'n confused. My car has almost 110k miles on it, and I don't know if the coolant has ever been changed, so I'm plan'n on doing that. I've changed coolant before in "normal" cars (like my brothers '95 Grand Am), bu never in a N*. Is there any reason I can't do the change myself? Also, I'm a little confused about where to put the tablets, and how many to use. Some posts say to use 2 tablets, some 4, some 6; how many is ideal? Also, some people are saying to put them in the lower hose, while others say to put them in the upper hose, and still others are saying to put them in the surge tank! AHHHHHHHHHH!!! Is there anything else special that I need to do or know about? BTW, I won't be doing this till next week, so take your time answering. Thank you!

Yes!, you do put the tabs in the bottom hose,...NEVER put them in the surge tank!
You can put 6 tabs in the system,it's not a problem.

Check the Technical archives at the top of this page,
Here's a direct link:-

http://www.cadillacforums.com/cadillac-tech.html#coolant

Hope this helps,

If you want a detailed explanation about the N* cooling system,I can post it here if you like,...it was written by a guy whom we often refer to as the "Guru",..he was/is part of the team that developed the Northstar, so he knows what he's talking about.

Regards
Mark.

The surge tank is a low flow area, so if you put the tabs in there, they will likely just sit on the bottom and clog the return line. They normally go in the radiator (high flow area), but since the Northstar does not have a "radiator" cap, the must go in a radiator hose (lower is recommended, but upper is easier, either will do). The FSM says to use 3 tabs, our old Guru said 6, FWIW I used 4.

It is no harder than any other car. After you do it run the RPM up to 3000 - 4000 RPM to purge any air in the system and then check the coolant level after cool down. Check it again after the first drive.

Premix the coolant before replacing it to ensure a 50/50 mix as you will not get all the old stuff out.

STS: you said If I wanted a detailed explanation about the N* cooling system, you could post it here. That would be greatly appreciated, if you have the time. Thanx.

Bare in mind that the following is in response to a question from an unknown forum member, don't know exactly what the question was though but it does'nt really matter.

Quote:-


Coolant temps in the range of 230 are perfectly normal and
desireable.

As long as the engine is "wet" and full of coolant that is
circulating it will not be damaged and can run as hot as 270 degrees
or hotter for EXTENDED periods of time without hurting a thing.

A system that has a 50/50 mix of ethylene-glycol coolant/distilled
water and is pressurized to 15 PSI (normal OEM cap) will not boil
until 265 degrees.

There is little to no correlation to ring belt deposits and coolant
operating temperature.

There are millions of Northstar engines on the road that operate
perfectly fine at those operating temperatures. You read about a few
problems on this and other forums....but...forums are like that.
Everyone with a problem looks up a forum for
help/information/commiseration/venting...but few look up a forum to
brag about their Northstar with 200K miles on it....

I have seen MANY endurance and durability engines that ran 100K
miles of heavy duty use in the Phoenix (GM Desert Proving Grounds)
area and off property in the hills and grades of the desert south
west. Those engines LIVED at high coolant temps all their lives and
they look fine inside. Better, in fact, than engines running "cool"
in cold climates.

I have personally run many high speed endurance engines on dyno test
(full power, 6000 RPM, 300 hours) at elevated coolant levels and the
engines just do not care if the coolant is at 210 or 250 or
180...... They hotter they run the better they look, actually.

Based on your observations of the coolant temp in your 96 ETC I
would ask...is this your first experience with a FWD car with
electric cooling fans..?? I suspect from what you say it may be as
the temperature excursions you observe are more a function of
electric cooling fans than anything else. Electric fan cooled cars
typically have fairly regular coolant temp excursions due to the
lack of air flow thru the radiator when the car is not moving. Older
cars with longitudinal engines (typical RWD) had engine mounted fans
that always pulled some air thru the radiator. Cars with electric
fans have NO airflow at low speeds and idle so the coolant temp
naturally creeps up...until the fans turn on...then the temps go
back down.

You will notice this much more in the winter and cool weather than
in the summer. In the summer, when the AC is on the fans will run
most all the time due to the requirement for constant airflow over
the condensor for the AC. The AC system has almost no thermal
inertia unlike the engine cooling system therefore it needs the
constant air flow. When the fans are running due to AC requirements
they provide radiator airflow by default so the coolant will
stabilize more at the stat temp. In ambients below about 40 degrees
the AC compressor is disabled (or when you drive on ECON or OFF) so
the fans only run when the coolant gets to 225F. That is perfectly
fine and is as designed. Seems odd at first to notice more coolant
temp swings at colder ambients but that is the nature of the beast
with electric cooling fans.

Putting a lower temperature stat in the engine is counterproductive
to the engine control system as many coolant thresholds in the
calibration are based on the operating temp of a 195 stat (which
usually controls around 205-210 in the engine) as designed AND the
stat control temp is closer to the fan turnon temp of 225 F Coolant
so as to minimize the amount of temperture cycling of the engine.
Putting a colder stat in increases the amount of cycling that you
are observing as the engine will cool down to the lower stat temp
when moving/fans on and then heat back up to the 225 fan on temp
when idling/city traffic.

It is desireable to get the coolant above 212 F so as to heat the
oil above 212 in city driving quickly so as to boil out moisture and
raw fuel that gets in the oil on cold starts. Running colder
thermostats is detrimental to engine life from this aspect,
particularily in colder climates and in short trip/urban driving
that doesn't heat the oil up otherwise.

The Northstar cooling system is a very sophisticated, high flow
system that is designed for a high output, high RPM, all aluminum
engine...not a system that was adapted from an older, slower
turning, cast iron, low output engine. The water pump on your 96
will pump around 105 gallons per minute at 6500 RPM (that is TWO 55
gallon drums in 60 seconds....think about it) while requiring a
minimum of power to do it. It is a very efficient water pump
impeller design that is designed to turn high RPM and move a lot of
water.

The main consideration of an all aluminum engine is NOT the absolute
coolant temps observed but maintaining thermal stability throughout
the engine. Keeping the hot spots cool and the cool spots hot
eliminates thermal fatigue of gaskets and seals and allows the
engine to "grow" and "shrink" with coolant temp changes as a single
entity...not dissimilar parts that stress the fasteners and gaskets.
This is accomplished by having VERY HIGH coolant flow rates thru the
block and heads constantly so as to maintain an even temperature
gradient across the engine regardless of the observed coolant temp.

Keeping in mind that the water pump can pump about 105 GPM at
6500.....only about 45 GPM is directed to the radiator. That is
sufficient for the heat rejection required and is the maximum that
is allowable for the long term life of the radiator....erosion of
the tubes, tanks, and end-tank oil coolers would result with more
flow. So....where does the other 60 GPM go....???....it is
recirculate back thru the block and heads in a re-circulation
loop....part of which is the heater core circuit which accounts for
about 7 GPM of flow at maximum engine RPM. The main part of the
recirculation circuit is the cast passages inside the water
crossover casting that the water pump resides in. When you remove
the stat you can see one of the coolant bypass passages at the end
of the thermostat mounting port...the large hole that the spring
loaded paddle covers.

The inlet thermostat design is used to minimize the efficiency of
the water pump and to limit thermostat induced temperature cycling
in colder weather. The stat has many functions. The spring loaded
paddle at the end closes off the bypass port (the bypass that
bypasses that 60 GPM back thru the heads and block) until sufficient
coolant pressure blows it off and establishes flow. Under normal
conditions the temperature sensing element is bathed in the bypass
flow consisting of the direct bypass port, the heater core circute
and "cold" water that is being admitted by the thermostat. This lets
the stat see a true operating temp of the engine as opposed to a
more conventional exit side stat that only sees coolant temp when it
opens and coolant is flowing past. Nothing wrong with your
eyesight....you just have to dig into the engine and the passages in
the castings to understand the cooling flow path...or get a service
manual and it is spelled out very clearly in a nice diagram for you.

The water pump in the Northstar is prone to "vapor lock" if it
injests any air bubbles so the water pump cavity is continuously
bled or air or bubbles thru the vapor vent line that is the 3/8 hose
leading from beside the upper radiator hose to the pressurized surge
tank.

The system uses a pressurized surge tank as the high point of the
system so as to de-aireate the coolant in a quiet, low flow area,
allow for expansion and contraction of the coolant, provide a means
of real time low coolant level warning BEFORE it impacts cooling
capacity, and, primarily, provide a source of clear, pressurized
coolant directly to the water pump inlet port to prevent the pump
from cavitating in high demand situations. The heater core circuit
exits the water crossover casting after the coolant traverses the
block/heads and returns thru the circuit from the pressurized surge
tank to complete the circuit and supply a constant feed of fully
pressurized coolant to the water pump inlet where the negative
pressure would be the greatest and cause cavitation.


Before you start redesigning or re-engineering the cooling sytsem on
the Northstar engine you really need to understand how it works, why
it is designed the way it is and what the impact of your design
changes are. There are thousands of hours of development time in the
cooling system of the Northstar and the vehicles it is installed in.
It was not taken lightly, trust me. Basically, it serves as a very
good example of a high performance cooling system for a high out put
engine. There is nothing that was compromised on the cooling system
design and the design features pioneered on that system in 1993 have
been incorporated in other high performance cooling systems
throughout the automotive industry....i.e...pressurized surge tanks,
vapor vent lines and continuous air bleed systems, inlet side
thermostats, high bypass ratio cooling porting, very high flow water
pumps, etc....


BAsically, every thing you did is perfect to make sure the system is
in top operating condition. The one thing you did not mention is the
addition of the GM Coolant Supplement pellets to the system to guard
against any incidental leaks from porosity in one of the aluminum
castings or a gasket imperfection. It is designated as a required
item in the cooling system. Search the archives using "coolant
supplement" as a topic and read my posts for more info on this as
much has already been posted.

You are, however, trying to fix something that is NOT broke. Put the
OEM stat back in as that is what is best for the car and engine. It
will actually reduce the level of coolant temp swings you are seeing
in cold weather, will warm the engine to the temperatures the
clearances were set up for, will match the PCM calibration set
points for coolant temperature and it will improve the oil life and
oil quality particularily in cold weather. Keep the system full of
50/50 Texaco DexCool/distilled water and install the 6 coolant
supplement pellets into one of the radiator hoses....not the surge
tank.


YOu make a good point about the thermal distress that can be caused
by continual coolant temp changes...to a degree this is a concern
and something that the engine developement engineers take into
account. Thermal fatigue of gaskets and such is what it is called.
The problem or concern is mitigated, however, by the very high flow
rate of coolant thru the engine, the high rate of coolant bypass
that is already heated by the engine and is simply bypassed to
stabilize the internal temps and the higher operating range of the
OEM stat that more closely matches the coolant temp that the
electric fans engage at. Lowering that stat temp with a "180" stat
makes the situation WORSE not better. The thermal fatigue issue of
the gaskets and engine internally is also mitigated by the fact that
the WHOLE engine structure changes at once due to the high coolant
flow rates. If the parts all grow and move and shrink TOGETHER then
there is minimal fatigue of the gaskets and such. This is one reason
the engine lasts as well as it does in fact. Most all of the head
gasket problems and such mentioned on this forum are on engines that
have well over 100K on them...unheard of 20 years ago. Furthermore,
when dissassembled for repair, the engine looked like new inside with
nothing other than head gaskets and (occasionally) a head bolt
thread repair. If the cooling system was not working correctly on an
all aluminum engine that turns 6500 regularily and makes over 1 HP
per cubic inch it would fail MUCH sooner.

Thank you. That's very interesting.

Man, I sure do miss that guy around here...

yes it is!

I put my 4 tabs in the upper hose. It's much easier to get to and doesn't hurt anything. The only place you dont want to put them is in the surge tank.

What would happen if I crushed the tablets, then dissolved and mixed them with the new coolant before refilling? Thus, I would be able to eliminate disconnecting the lower hose.

That should work. I have heard of others doing it. Just be sure they are thoroughly disolved.

putting them in the surge tank is the easiest but the worst place to put them. they will just sit there and wont get circulated, probably wont even break down like they should.
Kind of defeats the purpose of using them if they are put there.