Yikes....fingers crossed its not. I always assumed that anything after 260*F+ was considered unsafe for the heads.A shame, because I was really enjoying the scenic drive through WI, and how well the truck was running / performing. Oh well... at least I didn't blow the head gaskets (hopefully). Looks like I'd have to get past 260F (?) to warp the heads, but I won't know for sure unless I remove them.