How to back flush closed system???

SOURCE: How can I flush my whole coolant system

Preferable to flush as much out as possible to get rid of the old stuff and can be done at home by undoing the heater hose at the fire wall and using the garden hose to force water through until it comes out clean Dont turn hose on full blast as it will spray out over everything build up to it so it doesnt make a mess.Make sure the heater is in the on position so that water comes out the pipe you took the hose off.Either way though it will still be ok to just undo the bottom radiator hose as the majority of it will come out.

SOURCE: Our 1996 Pontiac Grand am was over heating today,

Your Grand Am only has the reservoir to add coolant to, there is no radiator cap. If the car overheated again, yes, you may not have put enough coolant in, or you've got a very bad leak somewhere.
Check under the vehicle for evidence of coolant. A leak can be difficult to find, as the coolant is blown around by the engine cooling fan, and just the speed involved in driving on the highway. You can check for leaks from above. If u find no evidence (best time to check is right after driving the car and it's at normal operating temp.) jack up the car, put on safety stands, block the wheels, and look under the engine for leaks. It could be the water pump, a hose, the radiator. Dry off wet areas w/ a rag (careful, everything is hot) and try to see where the origin of the leak is. Good Luck, let me know what u find.

SOURCE: Overheating Fiero

well fieros are very different cars you need to fill collent in a speical way so air doesnt get in the lines most fiero owners do not know this but it very important The best way to tell it is for wikipedia
Cooling system issues
With an already hot normal operating temperature of 220 °F (104 °C) prior to the recall switching to a 195 °F (91 °C) thermostat, the mid-mounted engine utilized long pipes to carry coolant to the front-mounted radiator. This demanded that a special coolant filling procedure be followed to prevent severe overheating. Simply pouring coolant into the thermostat housing (on the engine) would leave an air bubble in the radiator, while adding coolant just to the radiator would leave an air bubble in the engine's coolant passages. Proper procedure (with engine idling and the thermostat removed, filling the thermostat housing, burping the bubble out of the radiator by cracking open the radiator cap until coolant exits) must be followed in order to ensure an air-free cooling system.
A second problem has become common as more Fieros are being serviced by shops unfamiliar with their design. The under-body coolant tubes are positioned in such a way that a casual glance beneath the car will not suggest their fragility. As a result, many have been crushed by shop lifts, resulting in a near complete lack of engine cooling. The age of the car means that even GM dealerships may now be unaware of the proper jacking methods.
Lastly, the absence of a spare tire (at the front of the car, right behind the radiator) could have an effect on coolant system performance. i dont know who wrote this and i dont take credit for it

SOURCE: My 2002 pontiac grand prix

Hello, kevans222 and thank you for asking your question on Fixya!

Here is a simple process that will walk you through a few steps that will pinpoint the overheating problem on your 2002 Pontiac Grand Prix, without even using any tools. It has helped millions of people, and I am certain that it will help you, because I wrote it for people in your exact situation.
How to diagnose your overheating 2002 Pontiac Grand Prix

Get more great money saving tips and tricks about your vehicle from: twitter.com/acoates23234

Thanks for the vote, and good luck!

SOURCE: Why does it keep overheating 2003 Pontiac Grand AM V6

Head Gasket still--- not done correctly