Well I think my head gaskets are blown, or almost. Symptoms?

Proper coolant level in the surge tank is half full, cold. If you try to keep the surge tank full, or close to it, the normal coolant expansion as system temperature rises (and hard hoses are normal) will blow off excess coolant.

Check the pressure cap for sealing ability - the rubber cap seals or the surge tank neck must offer a perfect surface for sealing - or the system never develops proper pressure leading to boilover at about 224 degrees.

Have you done a cylinder block exhaust gas test ? Rent the test kit from any large parts store, read the instructions, and bubble the test fluid for 20 - 30 seconds immediately after a drive. You sample the airspace over the coolant in the surge tank, not the coolant itself. ANY coolant enters the test fluid and you wash everything and start over.

If you want to see what a positive test for exhaust gas components looks like, sample the exhaust pipe gas at idle.

USA-1 said:

Bascically my antifreeze keeps draining out the over flow. It's seems when I'm driving it builds pressure in the coolant system, and drains coolant. Is this a sign of head gasket failure? I'm constantly adding coolant. It's not smoking white. But I fear the worst.

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It's seems when I'm driving it builds pressure in the coolant system
that is correct -
as the coolant heats up - it expands - thus building pressure -

check these things out -

serge tank should be about half full when cold -

check the PURGE LINE for a constant gentle flow of coolant -
from the T-stat housing to the serge tank -

pressure test the cap -
be sure it maintains 15 - or 18psi -

if all the above is/was correct -
you need to do a BLOCK TEST -
the definitive test for failed head gaskets in the Northstar motor -

Other tell tale signs are radiator hoses still being hard after the engine cools down to ambient temperature, typically overnight. That would indicate combustion gasses adding pressure to the cooling system. Any pressure introduced from an external source like a combustion leak would remain after the system cools down leaving your radiator hoses stiff.

Morning misfire, car runs rough for the first 5 seconds after a cold start from coolant slowly entering cylinder(s) overnight

Gassy smell in the coolant tank or exhaust that smells like burning coolant on start up. The latter would smell like maple syrup.

If you're certain it's coming from the coolant overflow hose, it could simply be a poorly sealing coolant cap. Cheap enough to swap in a new one. Standard issue AC Delco caps are plentiful and is what is on mine. Also make sure you're using a 50/50 coolant water mix.

unimoged said:

Presently I am running a 160 deg F with no codes.

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Bad practice. Many of the emissions calibrations are set to change loop types at or near 160 degrees coolant temperature. Also, engine efficiency suffers a bit. (Your engine has a perfectly good high flow CAI, so that's not an issue with coolant temps.)

The proper thermostat is set to begin opening at 188 and be fully open at 206. The engine will run art from 192 to 200 degrees or so winter and summer, highway or traffic - so the thermostat is almost never fully open, except when in heavy traffic, no A/C function set, and the coolant warms to 224, fans go to SLOW and it cools to 213, fans turn OFF, cycle repeats until you get moving again.

Please study the several sticky posts on this in the main Engines; Northstar page and also study the entire Cadillac Technical Archive way up ^^^ in the top black bar - it was written by one of the GM Northstar System engineers.

Whether the car has this 180 degree sweep gauge or the earlier 135 degree sweep, the temperature indication marks are the same.

It is perfectly normal for any of these engines to warm into the green dot area in traffic.