Here's why it's complicated and why you should likely take it to a mechanic:
* Intake Manifold Removal: Accessing the thermostat typically involves removing the intake manifold, a complex procedure requiring various tools and knowledge of coolant system components.
* Coolant Drain: You'll need to drain the engine coolant completely before attempting any work on the thermostat.
* Potential for Damage: Improper removal or reinstallation of the intake manifold can damage gaskets, sensors, or other engine components.
* Specific Tools: You'll need specialized tools, including possibly a torque wrench to ensure proper tightening of manifold bolts.
Instead of attempting this yourself, it's highly recommended you take your 2004 Chevy Impala to a qualified mechanic. The cost of professional repair will likely be less than the cost of potential damage caused by an incorrect DIY attempt. A faulty thermostat replacement can lead to engine overheating and serious damage.