SlackBuildsOrg/system/mbpfan

mbpfan (fan control daemon for Apple MacBookPro machines)

A simple daemon to control fan speed on all MacBook/MacBook Pros
(probably all Apple computers) for Linux Kernel 3 and newer.

After installation you must add below to /etc/rc.d/rc.local:

if [ -x /etc/rc.d/rc.mbpfan ]; then
  /etc/rc.d/rc.mbpfan start
fi

and ensure /etc/rc.d/rc.mbpfan is exec (0755)

Also edit /etc/mbpfan.conf and uncomment min_fan1_speed & max_fan1_speed
I have found a min of 3000 and max 6200 work well for my mbp.