Agreed... internal case temps should be in the 35-40C
range (tops, 30-35C is better), drive temps of 40-45C.
Get a hard drive fan, or a 5.25" bay mount cooler (mount
the 3.5" drive in the cooler, stick the result in a
5.25" external bay), or get a good case with proper
airflow and/or fans that draw air across the hard
drives. (Antec Sonata, Antec p160 both have good setups
including a 120mm fan mount to draw air across the 4
internal drive mounts.)