Radiator fluid (7)
I believe the answer is:
coolant
'radiator fluid' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for coolant that I've seen before include "used to prevent overheating" , "Fluid circulating in an engine or reactor" , "Liquid or gas used to remove heat from something" , "One must lower the temperature" , "This takes heat out of situation" .)