Scale of new rant about good by church (10)
I believe the answer is:
centigrade
'scale' is the definition.
(I've seen this before)
'rant about good by church' is the wordplay.
'rant' becomes 'tirade' (both can mean an angry outburst).
'about' is an insertion indicator.
'good' becomes 'g' (abbreviation).
'by' is a charade indicator (letters next to each other).
'church' becomes 'cen' (I can't justify this - if you can you should give a lot more credence to this answer).
'tirade' going around 'g' is 'tigrade'.
'tigrade' after 'cen' is 'CENTIGRADE'.
'of new' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for centigrade that I've seen before include "scale" , "C" , "measure of warmth" .)