Where is the thermostat located on a 2003 Oldsmobile Alero?

The thermostat on a 2003 Oldsmobile Alero is located behind the engine, on the engine block, near the water pump. It's not easily accessible and requires removing some parts to reach it. You'll likely need to consult a repair manual specific to your Alero's engine (likely a 2.2L Ecotec or a 3.4L V6) for precise location and removal instructions. A visual inspection with the help of diagrams from a repair manual would be the best approach.