The thermostat in a 2005 Chrysler 300 is located
on the engine, typically at the lower part of the engine near the water pump. You'll need to consult a repair manual specific to your 300's engine (e.g., 2.7L, 3.5L, 5.7L, or 6.1L Hemi) for precise location. The manual will have diagrams showing its exact placement.
Accessing it usually involves removing some coolant hoses and possibly other components. This is not a beginner-level repair.
