QNAP reboots every 16 hours or so

Connect to your QNAP with a terminal and look in /mnt/HDA_ROOT/.logs. Specifically, kmsg. You should see a lot of deep information for your perusal, interpretation, and ultimate edification.

Another option is going to the Web UI >> Select System Administration >> System Logs >> tabs across the top will give you UI access to various files.

As for what to look for, it's usually a crap shoot of what looks bad, and what Google tells you is worse.

if you enable ssh login then

ssh admin@<qnap_ip_addr_here>
password: admin

then look at /var/log

grep ERR *log

look at hal_lib.log and hal_lib.log.bak specifically

look for stuff like this. I don't think my HDD was 60C and am suspicious about whether sometimes HDD temp is read incorrectly. It's possible these are setting thresholds not the actual readings. Not sure.

hal_lib.log:Get_Temp_Threshold() called, SYS_ERROR_TEMP=70
hal_lib.log:Get_Temp_Threshold() called, HDD_ERROR_TEMP=60
hal_lib.log:Get_Temp_Threshold() called, CPU_ERROR_TEMP=85
hal_lib.log:Get_Temp_Threshold() called, CPU_ERROR_TEMP=85

I'm also curious if other people see this:

manaRequest.cgi:Tue Oct 21 16:45:48 2014
PD_Is_Exist: can't retrieve port_id value!
hal_daemon:Tue Oct 21 16:45:59 2014
root_get_fan_speed(978): NOT implement.
se_sys_get_SAS_HBA_info(3606):System Error.
disk_manage.cgi:Tue Oct 21 16:46:03 2014

you may want to go inside the QNAP qui (hardware) and disable smart fan speed setting and switch to manual speed (medium always?)

when it says "root_get_fan_speed(979): NOT implement." I'm suspicious. Since fan speed seems correct in the gui. ~9k when I choose medium, and >10k when high speed is chosen