Why does your car overheat when heater is off?

Your car may overheat when the heater is off due to a malfunctioning cooling system, such as a faulty thermostat that fails to open, restricting coolant flow. Additionally, a leak in the cooling system, a broken water pump, or a clogged radiator can prevent efficient heat dissipation. Lastly, low coolant levels can also lead to overheating, as there isn't enough fluid to regulate engine temperature. Regular maintenance is essential to prevent these issues.