My 2002 Oldsmobile Silhouette keeps overheating. We replaced the thermostat and flushed the system by adding new antifreeze. The air blows cold from the heater when the car starts to overheat. Once

The vehicle will overheat if the cooling system is not properly filled with coolant and all the air bled from the system. With the system full and void of air, you then must assess the operation of the rad fans for proper operation as well as t-stat operation

Thermostat is stuck. Not sure about the added antifreeze, but might be good idea to flush system while changing thermostat.

Engine temperature is too hot. Better not run it till you find the problem, or you may need new head gaskets. Try changing thermostats, flush and refill with correct mixture antifreeze and water. If still overheating, get it to a shop for diagnosing.

You have a head gasket problem with the engine generating abnormal pressure, and sending all the antifreeze to the reservoir, thereby leaving the engine running dry; it is dangerous for the water pump to operate with no water.
Drill 3 11/64 or 3/16" holes in the thermostat side facing the engine, making sure not to touch the opening mechanism; this will keep antifreeze always running thereby, compensating for the abnormal pressure regenated by head gasket leak(s).
Your thermostat was never your problem.
In cold weather, 5 degress celsius or under, the thermostat takes longer to open and more antifreeze will be sent to the reservoir leading to an overheating.. Partially cover the radiator with a sheet metal piece to make the thermostat open faster and stay open, as the antifreeze is not being cold that much by cold air. You're fooling the cooling system into warm weather driving.
Don't waste your money buying radiator stop leak or liquids to repair head gaskets; this will only corrode and make your radiator to eventually leak.

head gaskets are gone ,end of story .

The heater core could be clogged. If your antifreeze is orange , then it is Dexcool antifreeze which causes slime and sludge to build up in the cooling system. It can clog a heater core. My suggestion would be to drain and flush the entire cooling system with Prestone Super Flush. Put in a new thermostat while your at it. Refill the cooling system with a green antifreeze that is labeled compatible with aluminum engine parts and radiators.Do Not refill with Dexcool antifreeze.

Could be a bad intake manifold or head gasket. These are prone to that problem. If you are lucky you may only have an air bubble in your system. Fill the system with the bleeder screw open until antifreeze comes out and then seal it. Make sure you have enough antifreeze in the radiator itself, dont depend on the overflow bottle.

Overheating problems usually warrant some troubleshooting. First, check your antifreeze level. If it's low, replace it, run it for a couple of minutes with your heater on, then recheck it. Next, your thermostat could be stuck. For about 30 minutes worth of work, and about $10 of parts, you can do this replacement yourself. This will usually give you the symptoms of having one coolant hose being hot and the other cool, if it's the thermostat that's stuck closed. The next place to look is the water pump. There aren't too many reliable ways of testing one of these at home, so it's pretty much a replace and pray, because if it isn't, then it's something more serious like a blown head gasket or a cracked head. These last two can disclose their presence by evidence of oil or antifreeze leakage, or white smoke when you first start up your vehicle in the morning, but will not always do this.

To check if it is the thermostat run the car and when the temp starts going up turn the heat on full blast in the car. If the temp goes down after you turn the heat on than it is your thermostat.

as long as the engine temperature is normal, i would suspect a clogged heater core, the dex-cool antifreeze is notorious for building up deposits in cooling system. have heater core flushed first to see if it makes any difference