AFTER instaling new belt run vehicle for about 15 min ,take a short drive to warm the belt material...then re check make sure belt snug not super tight..
check belt tension about every 15k...we dont have automatic tensioners on our cars we have mechanical[ 1980 technology ]... if using aftermarket pullys scuff the groved area with a scotch bright pad and brk cleaner to take off the glaze of billett pulleys....DONT USE BELT DRESSING on serp belts..it makes them come apart... any cracking and or glazing should make a belt make noise..