A IC car’s heating system normally taps into the engine’s cooling system, so that heat is mostly free. In a pinch you can actually turn the heater on full to help cool the radiator.
I had to do that when my radiator sprang a leak on the freeway and the engine heat kept creeping up. Unfortunately it was late summer and not at all pleasant.
I managed to get to a gas station with some stop leak in stock... If they didn't, I was ready to crack an egg in it.
I once rode in a friend's car in a similar situation. Very much not pleasant. His problem was a thermostat problem, so he hadn't lost all cooling but enough we used the same workaround. Running the heat in the summer time resulted in a couple of very sweaty dudes.
