2003 Lincoln Navigator burning smelll

When truck is on and in operation, smells like burning rubber, and saw smoke from passenger side, gauge, never goes past hot, but is a little higher than normal, no warning lights, also when the smell starts, it becomes a little stiff and rugged when driving, mechanic first say could be hose, cause he saw moisture on and around the belt, but now saying radiator replacement, I just need a idea of possibilities, thank you.