Ok,I have a 2002Firebird 3.8 seriesII, V6 coolant/water is coming up from radiator with cap off.

Do you have the right mix on the coolant you have in the engine? Could you have trapped air in the coolant system, did you have the heater system on when you were filling up with coolant. I assume you changed the radiator cap when you replaced radiator. I guess it could be caused by headgasket, are you loosing coolant, does oil look milky or oil in coolant. Belo link list a few things to look at but you have addressed most of them.
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There can be numerous reasons for coolant loss.

External Coolant loss
1. Coolant escaping from the radiator cap. Replace the cap.

2. There is an external leak in the system which could be from a hole or crack in the radiator(especially the plastic sections) or a hole in a radiator hose or there is a loose hose connection.

3. The water pump gasket has deteriorated and coolant is escaping from around the water pump fitting.

4. There is a crack in the coolant overflow reservoir and coolant is leaking out.

Internal Coolant Loss
1. Coolant is escaping into the engine's cylinders in which event you will see white smoke coming out of the exhaust and you will also have combustion gasses leaking into the coolant passages which will cause bubbles and overheating of the coolant. This problem will be due to a failed cylinder head gasket, a crack in the cylinder head or both.

2. Coolant is escaping into the engine lubrication system and in that event you will see evidence of coolant in the engine oil. Pull the oil dipstick and check the condition of the oil. If it looks a bit like chocolate milk and not just normal oil colouring you have coolant in there. Also check the radiator cap when the engine is cold. There may also be evidence of oil in the radiator coolant that is stuck to the radiator cap and around the neck of the radiator.
This problem will also be due to a failed cylinder head gasket or a crack in the cylinder head or both.

Whatever the cause in your case don't hesitate to have it checked out by a competent professional If you lose coolant and you allow the level to run significantly lower than normal the engine will overheat and you will cause very expensive engine damage.

Probably the water pump, when the engine is completely cool, open the radiator cap, start the engine, turn on the heat full, and check to see if you have circulation at the radiator cap nosal you should see movement of water if pump is good....

If it over heated before the thermostat, replace the radiator cap. Make sure the coolant (recommend just water until this is fixed) is full. When disconnecting the upper hose you lose all the coolant from the engine and about 1/3 of the coolant in the radiator. If you only full the radiator you don't have enough water. The new remonstrate needs to open for you to get enough water. In short- take radiator cap off. Start the engine. Fill radiator. Watch level for 5min, filling as needed.

If the coolant was hot when you noticed water coming out the radiator, that is normal from the heat expansion of the coolant. That is why there are coolant overflow tanks-also called coolant expansion tanks.
When refilling coolant, always top up the radiator, and fill the overflow tank to at least the cold mark level (about half-way up on the tank). With cap off, run engine till the thermostat opens- upper radiator hose will become hot-then shut off engine, add coolant to radiator as needed, replace cap. This method of filling will help to expel any trapped air in the system. Oh, and remember to set your heater controls on high when filling coolant, so the heater core and lines also circulate and expel air.
Check the seal on the radiator cap that it is still good. The cap seal is important to seal the coolant system, as it is a closed system under about 15 psi of pressure. The reason to pressurize the system is that the pressure will raise the boiling point of the coolant by about 10 degrees- important when you consider how hot the coolant has to be when running. OK, enough tutorial-I don't think you have a problem with the water pump! G'd luck, reeve.

i have the same problem. it may be a good idea to try and flush all the hoses individually. are you seeing any yellow mustard like gunk on your radiator cap? i took off my water pump and everything seems to be ok with it. here's a few things to check up on. the water pump, the radiator cap may need to be replaced because it may be losing pressure. could be a crack in the radiator, or a soft/week hose. you could take it to a shop and have them do a pressure test to help narrow down the problem.

OK, let's see, first, is it coolant or water? Coolant boils at 265 in a closed system, water boils at 220. Can you see any oil floating on top of water in radiator? Do you notice steam coming out the tail pipe at all? Is the radiator full of white rock looking stuff? Check the oil. And check all the above. If none of those symptoms show up, I would suspect just a clogged up radiator. A radiator shop can recore it or replace it. Hope this helps.

REPLACE THERMOSTAT AND RADIATOR PRESSURE CAP.IF CAR OVER HEATING WHILE IN MOTION.MORE LIKELY ITS THE THERMOSTAT,LOW COOLANT IN RADIATOR OR COOLANT SYSTEM,BAD WATER PUMP,WATER PUMP WEEP HOLE IS LEAKING, WATER PUMP NEEDS REPLACING.CHECK ENGINE OIL,IF OIL LOOKS LIKE MILK SHAKE YOU HAVE LEAKING HEAD GASKET.IF CAR IN PARK AND OVER HEATS WHILE IN A LONG TRAFFIC LINE OR.BANK DRIVE THROUGH COOLANT FAN NOT TURNING ON, BECAUSE THE ENGINE COOLANT TEMPERATURE SENSOR FAULTY.CODE SCAN CAR FOR FAULTY COOLANT FAN RELAY OR FAULTY PCM. CHECK COOLANT FAN FUSE, AND HOT WIRE THE COOLANT FAN TO MAKE SURE ITS WORKING.IF COOLANT FAN DONT WORK WHEN HOT WIRED. COOLANT FAN NEEDS REPLACING. REPLACE BOTH RADIATOR HOSES, REPLACE THERMOSTAT AND RADIATOR PRESSURE CAP.BUY NEW COOLANT ADD 50/50 WATER AND COOLANT.IF ENGINE OIL HAS ANTIFREEZE IN IT.REPLACE ENGINE OIL AND OIL FILTER TO KEEP FROM LOCKING UP THE ENGINE.GET CAR FIX.DONT KEEP DRIVING IF IT KEEP OVER HEATING,ENGINE DAMAGE WILL OCCUR.I HOPE INFORMATION I GAVE YOU WILL FIX PROBLEM.PROBLEM COULD BE LEAKING RADIATOR HOSES BUT CHANGE THERMOSTAT THATS FIRST THING I WOULD CHANGE BECAUSE IF IT CLOSED, ENGINE WILL OVER HEAT AND CRACK CYLINDER HEAD OR CRACK PISTON, COOLANT NEED TO CIRCULATE THROUGH THE ENGINE TO TAKE AWAY THE HEAT FROM ENGINE.

with my experiance on these engines it's usually the upper outlet hoses running from the heads into a t then into the upper radiator hose they are pain to replace but 3 out of 3 of my v6 isuzu's have had the same problem you'll have to pull off the theromstat and the coil pack the hoses are very small and run from the end of the heads one on each into a t then into the radiator hose just under the housing

hi its rob cylender head or cylender head gasket or ileak in cooling system check oil for creamy white sludge if non then take of radiator cap start engine see if it bubbles up turn of engine and smell into the radiator for fuel check accesive amounts of water or white smoke coming from tailpipe ether one of these maens cylender head of gasket blown