13 years ago
Near as I can figure, using a few different web sites, the distance is between 1600 and 1650 miles. Since Mexico is metric, that'd be between 2575 and 2655 klicks. As for how long, on good roads you could do this in two days. In this case, better plan for four days.
You drive down Highway 59 to Corpus, and Highway 77 to Brownsville. That's 350 miles (565 klicks).
You cross the border into Mexico. Take Highway 101 south for about 150 klicks until you hit Highway 180. Take Highway 180 all the way to Villahermosa. From there you take Highway 186 all the way to just west of Chetumal. In addition, while it might be a longer distance, take the Mexican toll road system. It'll take less time. Much better roads. It'll cost about 600 pesos ($50) on your route, though.
Click the button at right that says "Traza tu Ruta"
You then cross the border into Belize. There's some tiny little two lane road that goes south, through Corozal, Buena Vista, Orange Walk, and then to Belize City. It is called the "Northern Highway" and it claims to be paved.
You'll have to have the car insured in the United States and Mexico at the very least.