Heater that's cooler for car (8)
I believe the answer is:
radiator
'heater' is the definition.
(radiator is a kind of heater)
'cooler for car' is the wordplay.
I cannot quite see how this works, but
'for' could be 'to' (eg both can mean 'in the opinion of') and 'to' is located in the answer.
This may be the basis of clue (or it may be nonsense).
'that's' is the link.
Can you help me to learn more?
(Other definitions for radiator that I've seen before include "It spreads heat as in house" , "Apparatus for heating" , "It spreads heat around room or cools engine" , "Heater -- or cooler!" , "Room warmer" .)