The preparation continues

Parts we have replaced before the trip (just in case)
Radiator
Spark plugs
Spark plugs casing
Spark plugs wires
All engine belts
Service the AC
Transition oil
Engine oil
Tires
Breaks
Shocks
Wipers
Timing belt
All engine houses


Documents and insurance information
Birth Certificates and Notary Spanish Translations (make photocopies)
Certificate of naturalization (make copies)
Car Proof of ownership (make copies)
Valid vehicle registration certificate (make copies)
Vehicle Invoice (make copies)
Central American Insurance Requirements (make copies)
Importacion General de Vehiculo (Mexico) (can be done 180 days before the trip)
Mexican Tourist Card (The paperwork for the Mexican Tourist Card is processed in the immigration office at the customs checkpoint)
NO visa requirements for US Citizens
List (English/Spanish) of all items that you are bringing in the car make copies)
I am sure there will be more or less requirements as the time passes from the date I wrote this list, so call the consulates of the countries you are crossing to get the latest information.