On the GL X3000, the Web UI only allows setting the fan start temperature as low as 70°C. At first glance that feels a bit high, but it is probably fine.

The AP MT7981B is specified for an operating temperature range of -40°C to 125°C, so 70°C is well within spec (1). Still, I wanted the fan to kick in earlier because I am dealing with unwanted random restarts and I wanted to reduce heat as a possible factor. Mine was idling at around 65°C, so waiting until 70°C meant the fan would barely ever run. And honestly, I would rather have a bit more airflow than trust that every single component inside the box is equally happy at those temps.
Here is how to change the fan activation threshold over SSH.
Step 1: Connect via SSH
Step 2: Edit the fan config
Open the fan config file
vi /etc/config/glfan
You should see something like this
config globals 'globals'
option enabled '1'
option sysfs '/sys/devices/virtual/thermal/thermal_zone0/temp'
option warn_temperature '75'
option div '1000'
option temperature '50'
Code language: JavaScript (javascript)
The setting that controls when the fan starts is option temperature . Change it to the temperature where you want the fan to kick in. Save and exit.
Step 3: Restart the fan service
/etc/init.d/gl_fan restart
Done. The fan should now start at your new threshold.
Reference
