Here is a list of HDD's operating temperatures -
Disk Drive Temperature Range
It turns out that different drive models run at different temperatures, and this can throw off the stats when looking at the entire population. If in a given ambient air temperature, drive model A runs warmer than drive B, and drive A fails more, that will make it look like there is a correlation when there isn’t.
This table shows the average temperature, in degrees Celsius, of different drive models:
Model Avg. Temp (C)
Seagate Barracuda LP (ST31500541AS) 21.92
Seagate Desktop HDD.15 (ST4000DM000) 22.10
Seagate Barracuda Green (ST1500DL003) 22.86
Western Digital Red (WDC WD30EFRX) 23.05
Seagate Barracuda LP (ST32000542AS) 23.27
Western Digital Caviar Green (WDC WD30EZRX) 23.46
Seagate Barracuda 7200.14 (ST3000DM001) 24.71
Western Digital Caviar Green (WDC WD10EACS) 25.23
Seagate Barracuda XT (ST33000651AS) 25.40
Hitachi Deskstar 5K4000 (Hitachi HDS5C4040ALE630) 25.42
Seagate Barracuda 7200.11 (ST31500341AS) 25.73
Toshiba DT01ACA Series (TOSHIBA DT01ACA300) 25.82
Hitachi Deskstar 5K3000 (Hitachi HDS5C3030ALA630) 26.46
Hitachi Deskstar 7K3000 (Hitachi HDS723030ALA640) 26.75
HGST Deskstar 7K4000 (HGST HDS724040ALE640) 27.22
Hitachi Deskstar 7K2000 (Hitachi HDS722020ALA330) 27.39
HGST Megascale 4000 (HGST HMS5C4040ALE640) 27.84
Western Digital Caviar Green (WDC WD10EADS) 27.93
Seagate Barracuda XT (ST4000DX000) 30.54
As you can see that is not that hot, which is why you cant find a drive caddy with a fan, beacuse they dont need them.
If your drives are failing it is not due to heat, if it is you should buy better branded drives.
I would advise you look to switch them to SSD drives. You will get better performance and are less likely to fail due to less parts to fail.
For more information on heat related failure check this link - https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/