Like your engines cooling system radiator, the heater core can suffer some of the same issues. If the heater core becomes clogged with rust or sludge, you will no longer have heat. Also leaks can cause the inside of the car to be full of steam and even dirty your windows. If you smell the scent of coolant when your heater is on, chances are, you have a small leak in the heater core. Most vehicle heater cores are located under the dashboard, and replacing it is a major job, so keep the system serviced to avoid excessive repairs.