Q: can a car ventilate without being on?

Hi there. The question you have presented is somewhat confusing. I’m not sure, if you are actually putting a fan inside the car to circulate the air out of the vehicle or the radiator cooling fan runs after the vehicle is shut off. Putting a fan inside the car, would not do much to cool the inside with windows up. The fan running continuously off of the vehicle battery could run the battery down. The radiator cooling fan running after turning off the vehicle, may be normal operation. The engineers have incorporated this design, to keep engine temperatures from spiking once coolant flow has stopped. I recommend having your vehicle’s hotter than normal be diagnosed and repaired by a certified technician, such as one from YourMechanic.