Warranty running out for rusting Toyota frames Woman's rotted frame just missed free repair Every driver knows that road salt is not good for the underside of their car â but for owners of some popular pickup trucks, salt is even more dangerous because it can destroy their trucksâ frame. and last updated 2021-02-15 11:16:58-05 Many cars and trucks are covered with road salt this chilly February â salt that is not good for the underside of cars. In most cases, a car wash removes it, and there is no long-term harm. But for owners of some popular pickup trucks, salt is even more dangerous, because it can destroy their truck's frame.