i was driving on XXX south to grab some Mexican food for dinner. on the way at one point i smelled something burning like an oil smell. but didnt see anything and suspected it was the old car in front of me. and my f150 was running fine. when i got out at the restaurant i did not see or smell anything around the truck. i went in to find they were closing at 9:00pm and it was 8:40ish. so i left telling them id stop back another day. was driving north on XXX heading home when around the same area of [XXX] 51 I smelled something burning again. once again i didnt see any smoke around my truck, no one was beeping at me or anything. and the truck was running/working well. i figured maybe its someone with a fire in their yard. further down [XXX] about 300 ft before [XXX], i smelled smoke stronger this time and looked up and to my right and saw smoke pouring out of a vent or something on the headliner. realizing that the truck is obviously on fire i wanted to get it off the street asap so as to be less a danger to others. so i turned up [XXX] at the intersection and pulled off the side of the road as far off as i could get the truck. grabbed my phone from the passenger seat and exited the truck in a hurry. as i looked over at the truck i saw flames coming up from underneath between the cab and the bed of the truck - looked to be centered under the truck. i ran about 150 feet from the truck and called 911. i turned around as i was talking to the operator. and the truck was com