pretty much every slightly big town has diesel along highways 1 and 5, just be sure to fill up every chance you can and every time you are going off road. the total from mexicali to los cabos is 1500 km so that is about 2-3 tanks, you wont have trouble finding 2-3 gas stations offering diesel. anther tip, if there is a big port in town there's going to be diesel. some of the big towns and cities are Mexicali, Tecate, Tijuana, Ensenada, San Quintin, San Felipe, Bahia de los Angeles, Guerrero Negro, Santa Rosalia, Loreto, La Paz and Los Cabos. if you have any problem on the highway, lift your hood up, there is a highway patrol called green angels specially for drivers assist, they offer mechanic help and towing for free and they have some fuel for a fee, enjoy Mexico and have an awesome time