Before you buy any parts, run the car in your driveway and check to see if the thermostat opens, and then watch to see if the electric fan comes on, usually around the time the thermostat opens or shortly after. Do not run the AC while checking(if applicable.) Without any tools you can use a rag to feel the radiator hose leading to the thermostat housing. As the motor warms up and before the thermostat fully opens, the upper hose will retain pressure wich you can feel by squeezing the hose. It will be tight. Once the thermostat is fully open, the hose pressure drops enough that you can pinch the hose together with your hand(use a rag to prevent burning)and feel the coolant flowing. At this point it will be easy to squeeze compared to before it opens. If this is OK, then keep an eye on the cooling fan to see if it cycles on and off over a period of say 15-20 minutes. If this also works then you may have other problems including a cracked head wich is not uncommon on the GM Quad 4, 4 cylinder motors, radiator or water pump. Also, you can take the thermostat out for the summer and run the car like that without causing problems. Good luck sgf, let us know what you find.

Not a shadetree mechanic...no tree. Sounds like TSHTF? Or tell her only to stop for lights in Alaska. You must grease that infamous muffler bearing too! Glad to help ya!  Anytime! Where do I send the bill?  P.S. Where are the other 4 cylinders?