hladnjak

1. (in a car) radiator
   Procurio mi je hladnjak, moram kod majstora. — My radiator is leaking, I need to see a mechanic.
   Motor se pregreva jer je hladnjak zapušen. — The engine overheats because the radiator is clogged.
2. (in electronics) heat sink; cooler
   Kupio sam jači hladnjak za procesor. — I bought a better cooler for the CPU.

In Serbia a refrigerator is usually called frižider; hladnjak in this sense is more typical of Croatian usage.