1999 Pontiac Grand Am Overheating

aftermarket stereo would have nothing to do with engine cooling fans . The radio is not even on the class 2 data bus .

Relay Driven Dual Cooling Fan Diagnostics

This link may help you. Coolant Elbows Leaking 3800 Pontiac GM Chevy 3 8 Liter V6 engine water...

1: Drain coolant system
2: Purchase coolant flush, making sure you have the proper amount for your size of coolant system
3: Pour coolant flush into your radiator, filling the rest with water
4: On the coolant flush bottle it will tell you how long to run your vehicle
5: Once done running, let cool enough to open radiator cap, and drain system COMPLETELY by first draining out of pep **** on radiator, then taking one side of the hoses off the radiator and draining those
6: Put hoses back on and fill system with coolant. When the fluid gets to the top of the fill port on radiator, start vehicle and let run, allowing air to escape the system, and fill as necessary

These engines like the 3.8 usually have a intake leaking problem. Also the have plastic elbows on the passengers side of intake that go to heater hoses can leak also. Is it a 3.8 liter engine in your car. And where abouts does the fluid look like its coming from.

If it has an electric radiator fan (not AC fan) The radiator fan is not working. Possible coolant sensor or switch.

I would replace the rad, you've done everything else.

try priming the engine block & radiator with water though the hose's & any hose you can squeeze to pump out the air lock with the filler cap off when running, sounds too much air is is in the system & the pump won't work dry.
I had this problem a few times & I ended up practically forcing water into any hose I could re-attach quickly using a garden hose, as the heating system need's priming too !

dont think so,seem to remember a reostat somewhere at the bottom of the rad right hand side ,check for earth problems as well ,sorry if vague but i seem to be forgetting things as i get old .

If its the 3.1L it could be your intake manifold gasket , the material used for the gasket does not react well with GM's Dex-Cool antifreeze. The leak may not be apparent at first, but I would pressure test the cooling system. If you look at the front of the motor by the belts , try to peek down at the intake manifold and check for slight seapage to an obvious leak.

If its either of the Quad-4's they were notorious for heads warping or cracking.

I had the same problem on my 1999 Pontiac GA 3.4 litre. Replaced a bunch of stuff. It just kept pushing the coolant out the overflow once the temp got to 200 + like to drove me nuts. Ended up being that reservoir. If you measure the O.D. of the cap(brand new cap) and the I.D. of the reservoir filler neck there is no way it will seal(even tried to fit a different type cap,no luck). The system has to be able to build pressure or the coolant will boil out at 212. Causing the coolant to be pushed out the reservoir. Why? you say or How? did the filler neck increase in size. I dont know but GM has write ups about this problem. They say sand it with a piece of sandpaper to smooth it. Maybe someone sanded it way to much?? Around $40 bucks and I was on my way. Hope this helps someone.