I just installed ManjaroLinux 18.0.4 Illyria ('cat /etc/lsb-release') with XFCE and with 4.19.69 Kernel ('uname -r') on a MacBook Air 2013 -- I updated the packages and settled usual minor issues with broadcom drivers.
I have a problem that persists, namely that, 'sensors' gives me 'TH0a: +76.2°C' (I can also feel it on my legs) without any load ('top' shows that no swap is used, 1.79Gof free memory, and df -h shows more than 70G free space, same for 'iotop' or 'iostats').
I believe 'TH0a' refers to a sensor in my SSD (Apple SSD SD0128) and I believe the temperature is way too high -- especially if I compare it to the CPU temperature, which is 20° below).
Have you specific manips in mind that should be carried in order to address it? Let me know if you need more information.
Note: 1) Manjaro is the only OS installed on the MacBook (no dual boots). 2) Debian Stretch worked fine, a month before, on the very same laptop, 3) I can confirm that fans are working.
NB.: I have to confess that I encountered a similar issue when upgrading from Debian Stretch to Buster, and that was the ultimate trigger for switching to Manjaro.