To be sure, you should:
* Consult your owner's manual: This is the best resource for the exact location.
* Use a repair manual specific to your truck's year, make, model, and engine: These manuals have detailed diagrams and instructions.
* Search online for "2004 Dodge [Your Engine Size] thermostat location": Many forums and websites have pictures and discussions about this.
Do not attempt to locate and replace the thermostat unless you have experience working on vehicles. It involves working with hot coolant and can be a complex procedure.