Where is the thermostat housing located on 2001 Chevy Malibu?

On a 2001 Chevy Malibu, the thermostat housing is located at the top of the engine, at the rear of the engine block, just below and slightly behind the intake manifold. It's often near the water pump. You'll likely need to look down into that area between the engine and firewall to see it. Access may require removing some components depending on the specific engine (likely a 3.1L or 3.4L V6 in this year).