BFE,TEMP is a "structural" temperature not a thermal analysis temperature. Normally the nodal temperatures are of interest so nsol,2,node number,temp is used. I don't see a way to plot the average element temperature in post26 so you for that you have to use post1 as Matt mentioned:
/post1
set,,,,,time
etable,e_temp,temp
pretab,e_temp
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