[Dieselwrencher]

I used to work in a heavy truck frame shop. Without heating the frame rails you will more than likely never straighten the frame without damage to the metal and or the equipment. So yes you can heat them. I used to get the semi frames glowing red with about 25,000psi of force on them and would leave them until cool. On a heat treated frame, you do not want to quench them like mentioned. On these older frames it won't hurt them but I would just let it cool once put in a pull or bind used to help straighten them.