Where is the thermostat located on 2000 Chevy Malibu?

The thermostat on a 2000 Chevy Malibu is located under the intake manifold, on the engine. It's not easily accessible and requires removing various components to reach it. You'll likely need to consult a repair manual specific to your vehicle's engine (there were a few different engines offered in the 2000 Malibu) for detailed instructions and diagrams.