Fluid removing heat (7)
I believe the answer is:
coolant
'fluid removing heat' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for coolant that I've seen before include "part of heat exchanger" , "Fluid circulating in an engine or reactor" , "One should stop overheating" , "Heat-removing fluid" , "One must lower the temperature" .)